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| 16:00 | (Invited) In Situ TEM Observation of Oxygen Vacancy Driven Structural and Resistive Phase Transitions in La2/3Sr1/3MnO3 ABSTRACT. Lide Yao, Sampo Inkinen, Sebastiaan van Dijken NanoSpin, Department of Applied Physics, Aalto University School of Science, Finland sebastiaan.van.dijken@aalto.fi Oxygen defects can have a profound effect on the physical properties of transition metal oxides. Electric-field driven migration of oxygen vacancies provides a viable mechanism for the formation, rupture and reconstruction of conducting filaments in insulating oxides, an effect that is used in nanoscale resistive switching devices [1,2]. In complex oxides where magnetic, ferroelectric and superconducting phases emerge from strong correlations between localized transition metal valence electrons, oxygen vacancies can radically alter a plurality of intrinsic properties via valance changes and structural phase transitions [3]. The ability to reversibly control the concentration and profile of oxygen vacancies in oxide nanostructures would thus open up comprehensive prospects for new functional ionic devices. Advancements in this direction require experimental techniques that allow for simultaneous measurements of oxygen vacancy dynamics, atomic-scale structural effects and macroscopic physical properties. Here, we use in situ transmission electron microscopy (TEM) to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite film, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. [1] R. Waser and M. Aono, Nature Mater. 6, 833 (2007) [2] J.J. Yang, D.B. Strukov, and D.R. Stewart, Nature Nanotech. 8, 13 (2013) [3] S.V. Kalinin and N.A. Spaldin, Science 341, 858 (2013) |
| 16:30 | Probing a device’s active atoms ABSTRACT. M. Bowen1, M. Studniarek1,4, U. Halisdemir1, F. Schleicher1, B. Taudul1, E. Urbain1, S. Boukari1, M. Herve3, C-H. Lambert2, A. Hamadeh2, S. Petit-Watelot2, O. Zill1, D. Lacour2, L. Joly1, F. Scheurer1, G. Schmerber1, V. Da Costa1, A. Dixit1, P.-A. Guitard5, M. Acosta1, F. Leduc4, F. Chouekani4, E. Otero4, W. Wulfhekel3, F. Montaigne2, E. Monteblanco2, J. Arabski1, P. Ohresser4, E. Beaurepaire1, W. Weber1, M. Alouani1, M. Hehn2 1Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, F-67000 Strasbourg, France Our understanding of how devices operate has matured considerably in recent years. Separately conducted device and materials science studies (see e.g. this first report of clear-cut memristance in a spintronic device [1]) have been superseded in scientific insight by ‘operando’ studies that probe the device’s materials properties after the device has been placed in various states of operation. Of course, this approach equates all atoms in a device with its operation, though generally, only a subset of these atoms is actively involved. We propose as a next step in operando studies to focus the materials characterization technique onto only those atoms that drive the device’s operation. To do so, the materials science technique excitation is implemented, but the readout is performed within device operation. To demonstrate the technique’s interdisciplinary potential, we considered an extreme combination of device class and materials science technique. We’ve chosen magnetic tunnel junctions (MTJs), a spintronic device with industrial penetration toward next-generation memories and bio-inspired computing [2]. Because current flow through defects in the device’s tunnel barrier (e.g. oxygen vacancies [2]), this macroscale device operates using a minute subset of active atoms. To focus on solely these atoms, we deployed synchrotron-grade x-ray absorption spectroscopy, which resolves the electronic structure of specific dilute atomic species buried within a heterostructure. We’ve studied the MgO MTJ magnetotransport spectra upon sweeping the soft x-ray photon energy across the O K edge. RP exhibits changes associated with Fe oxide bonds parallel to the interface, while RAP does not. This association of Fe-O bonds parallel to the intefaces with high TMR, although counterintuitive since such oxides generally are thought to degrade TMR, was predicted theoretically [5]. We will also discuss experimentally and theoretically how this technique alters the MTJ’s spintronic operation. Our technique has the potential to considerably simplify progress in device studies spanning a wide interdisciplinary range of research fields. It also strengthens scientific causality between a device’s operation and the materials properties that underscore it, and thus touches upon the philosophy of scientific research itself. [1] Bias-crafted magnetic tunnel junctions with bistable spin-dependent states, M. Bowen et al., Appl. Phys. Lett. 89 103517 (2006). [2] Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO, F. Schleicher et al., Nature Comm. 5, 4547 (2014) |
| 16:50 | Applications of Electron microscopy imaging and spectroscopy to understand structure-properties relationships in complex functional materials ABSTRACT. N. Gauquelin1, G. Koster2, M. Huijben2, G. Rijnders2, S. van Aert1, and J. Verbeeck1 1EMAT, Department of Physics, University of Antwerp, Groenenborgerlaan 171, BE-2020, Antwerp, Belgium Nicolas.Gauquelin@uantwerpen.be The study of novel physical properties appearing when two materials are interfaced has become one of the major fields of research in solid state physics over the last decade. As the materials involved in those new physical phenomena are often complex oxides, many factors such as strain, oxygen stoichiometry, cation intermixing, confinement effects, electronic reconstructions, band bending, orbital ordering… have to be considered when discussing their origin. The exact understanding of those phenomena is a key factor in order to turn these research ideas into working devices and in order to search for the most optimal materials. If the two interfaced materials have different octahedral tilt systems, one has to adapt to the other [1]. Advances in electron microscopy instrumentation and techniques such as the appearance of aberration-correctors of the probe-forming lens have made it possible to achieve sub-angstrom spatial resolution allowing the study the material on an atom column by atom column basis. High Angle Annular Dark Field (HAADF) combined with Annular Bright Field (ABF) imaging has made it possible to image and understand respectively the cationic and the oxygen sub-lattices in these materials. Furthermore, improved stability and the appearance of electron monochromators has made an energy resolution of 100 meV readily available in Electron energy loss spectroscopy (EELS) offering the benefits of an X ray absorption (XAS)-like signal at atomic spatial resolution. I will be reporting recent results enlightening the effect of this oxygen octahedral coupling on the change of the magnetic easy-axis in some ferromagnetic manganite films.[1] I will show how this change of magnetism can be related to a change in hybridization between the metal and the oxygen orbitals [2]. A second example using RNiO3 (R = Sm, Nd) superlattices will demonstrate the relationship between metal-oxygen hybridization, oxygen octahedral tilt and metal-insulator transition [3]. [1] Z. Liao, M. Huijben, Z. Zhong, N. Gauquelin et al., Nat. Mater. 15, 425 (2016); Z. Liao, R. Green, N. Gauquelin, S. Macke et al., Adv. Funct. Mater. (2016) [2] Z. Liao, N. Gauquelin, R. Green, S. Macke, J. Gonnissen et al., submitted. M.H., G.K. and G.R. acknowledge funding from DESCO program of the Dutch Foundation for Fundamental Research on Matter (FOM) with financial support from the Netherlands Organization for Scientific Research (NWO). N.G. and J.V. acknowledge funding from the Research Foundation Flanders (FWO, Belgium) project 42/FA070100/6088 “nieuwe eigenschappen in complexe Oxides”. |
| 16:00 | (Invited) Multicaloric oxides ABSTRACT. X. Moya1, S. Crossley1, P. Lloveras2, M. Barrio2, J.-Ll. Tamarit2, E. Stern-Taulats3, A. Planes3, Ll. Mañosa3 and N. D. Mathur1 1Department of Materials Science, University of Cambridge, Cambridge, CB3 0FS, UK Thermal changes in oxides can be driven using magnetic fields, electric fields and hydrostatic pressures. The resulting magnetocaloric, electrocaloric and barocaloric effects are large near ferroic phase transitions, and have been proposed for environmentally friendly cooling applications. I will describe the fundamentals of these caloric effects from a historical perspective and present recent advances on multicaloric oxides. |
| 16:30 | Electrocaloric Refrigeration using Multi-Layer Capacitors and Fluid-assisted Thermal Regeneration. ABSTRACT. Hervé Strozyk, Romain Faye, Daniele Sette, Mathieu Gérard, Emmanuel Defay Luxembourg Institute of Science and Technology, 41 rue du Brill, 4422 Belvaux, Luxembourg In a time when the global warming cannot be ignored, conventionnal compression cooling devices are regarded with a critical eye. Indeed, utilized fluorocarbon fluids are known to induce global warming and also to act as ozone layer depleting gases. The caloric community is thus trying to move on new techniques. Our work is based on refrigeration devices exhibiting the electrocaloric (EC) cooling effect. The active material is based on Zr-doped BaTiO3, which appears in commercially available multi-layer capacitors (MLCs). When voltage is applied to the electrodes of the capacitors, they undergo a temperature increase. When voltage is released, the material then cools down. The applied voltage ranges from 100 to 200 V, which corresponds to temperature variation (positive or negative) ranging from 0.5 to 0.8 °C. This nominal effect is then coupled to a thermal regenerator. The function of this device is to use a thermal active substance to create a thermal gradient. The latter is the evidence of the ability of the device to act as a thermal pump. Our device consists of a fluid column partially into a cell that contains the active EC capacitors, and partially into elastomer hoses. The fluid, which is low viscosity silicone oil, is used both as heat storing material and as heat exchange medium. It is moved back and forth in contact with the MLCs. The motion is provided by a home-made peristaltic displacer based on the motion of a piston. The thermo-fluidic cycle is timed as follows. The top part of the fluid column is in contact with the EC material when the field is applied. Then the fluid is moved up while the field is maintained. When the fluid has reached its top position, the field is released, which infers that the EC material cools down. Consequently, the bottom part of the fluid column is also cooled down. After several repetition of the previous cycle, a thermal gradient takes place between the top and the bottom of the fluid column. This corresponds to the thermal equilibrium with the thermal losses. When 3 blocks of 50 MLCs are used to generate EC thermal regeneration, the best thermal gradient ΔT that can be obtained is 0.21 K after 700 s of running, under 140 V applied voltage. Refrigeration is obtained here, as temperature of the bottom part of the fluid column is decreased. The influence of different relevant parameters on the cooling performances of the system is also analysed. The direct influence of the voltage on ΔT is clear: the larger the voltage and the larger the temperature gradient. The heat exchange is also identified to be important for enhancing EC performances. In our system, this parameter corresponds to the thickness of fluid channels that permit the contact between cooling fluid and active material. The narrower the channel, the larger the speed of the fluid and thus the larger the heat exchange. This prototype gives the opportunity to identify the key design parameters for the next generation of EC coolers. |
| 16:50 | Screening and reliability of Multi Layer Capacitors for Electrocaloric cooling ABSTRACT. Romain Faye, Daniele Sette, Emmanuel Defaÿ Luxembourg Institute of Science and Technology, 41 rue du Brill L-4422 Belvaux, Luxembourg The electrocaloric community has recently been more and more involved in the development of prototypes in order to demonstrate that electrocaloric effect (ECE) can be used for new kinds of cooling devices. The existing prototypes are based on polymers, ceramics or even commercial multilayer capacitors (MLCs). In this study, we have considered MLCs playing the role of cooling device. The aim has been to identify some key parameters enabling to choose the most appropriate MLCs with respect to prototype design and cycling parameters. To do so, we have been interested in heat exchange, cooling power, efficiency and fatigue behaviour. Direct and indirect characterizations of ECE have already shown that some MLCs can exhibit a temperature difference up to 1K. Its multilayer design allows for applying large electric fields while maintaining a good “active material/electrode” volume ratio. The commercial availability of this electronic component is also a guarantee of reliability and robustness for standard usage. We made a screening of different commercial MLCs in order to compare their temperature change, caloric heat and electrical work. We have highlighted that Temperature change at 200 V can vary by 30 % between MLCs with the same specification from different providers. By using high frequency Infrared imaging (up to 600 Hz), we also observed the way the caloric heat is emitted or absorbed during the very first second. The maximum temperature change on the surface is reached less than 30 ms after the voltage application. Operating an EC cooling device requires continuous electrical cycling at a voltage value much higher than its standard specification. Depending on the cycling frequency the number of cycle can easily reach few hundreds of thousand per day. So it appears necessary to characterize the unipolar fatigue behaviour of this component and the possible strategy to restore its initial properties. After 500 000 cycles, a 23% decrease in maximum unipolar polarisation is observed. Finally, we will provide some elements concerning the strain induced by the application of an electric field. This piece of information can be interesting to define the best way to assemble MLCs together. These results can be considered as guideline to integrate MLCs into future prototypes. |
| 17:10 | Looking for improved caloric responses with ferroelectrics ABSTRACT. B. Dkhil Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, CNRS-UMR8580, Université Paris-Saclay, 92290 Châtenay-Malabry, France brahim.dkhil@centralesupelec.fr The search for alternative solid-state refrigeration materials to hazardous gases in conventional and cryogenic cooling devices is a very active field of condensed matter [1, 2]. The use of phase transitions is a powerful tool to achieve giant caloric effects in ferroic materials in which magnetization, polarization, strain and/or volume can be strongly tuned under a moderate external stimulus. Here, we explored various strategies to reveal ferroelectric potentialities as solid state coolers such as multiphase points composition, elasto- and baro-caloric responses, negative electrocaloric effect in antiferroelectrics as well as the use of dual-stimuli by taking advantage of multicaloric effects combining stress and electric field in ferroelectrics or magnetic and electric fields in multicalorics [3-7]. [1] X. Moya, S. Kar-Narayan, N. D. Mathur, Nat. Mater. 13, 439 (2014) [2] T. Correia and Q. Zhang (Eds.). Electrocaloric Materials, Springer: Berlin, 2014 [3] Y. Liu, J.F. Scott, B. Dkhil, APL Materials 4, 064109 (2016) [4] Y. Liu, B. Dkhil, E. Defay, ACS Energy Lett. 1, 521 (2016) [5] Y. Liu, L. C. Phillips, M. Bibes, A. Barthélémy, B. Dkhil, Nat. Comm. 7, 11614 (2016) [6] Y. Liu, J.F. Scott, B. Dkhil, Appl. Phys. Reviews 3, 031102 (2016) [7] Y. Liu, G. Zhang, Q. Li, L. Bellaiche, J.F. Scott, B. Dkhil, Q. Wang, Phys. Rev. B 94, 214113 (2016) |
| 17:30 | Hydro/solvothermal synthesis of various SnO2 nano/microstructures ABSTRACT. Kristaps Rubenis, Janis Locs Institute of General Chemical Engineering, Faculty of Materials Science and Applied Chemistry, Riga Technical University, 14/24 Azenes st., LV-1048, Riga, Latvia By changing the hydro/solvothermal synthesis parameters (temperature, holding time) or composition of the synthesis starting solution (reactants concentration, adding co-solvents or surfactants to the synthesis starting solution), morphology of the material being synthesized can be greatly altered and as a result different morphology dependent properties of it can be modified. In the present study we investigated how various hydrothermal synthesis parameters as well as changes in the composition of the synthesis starting solution affect crystal structure, morphology and specific surface area of hydro/solvothermaly synthesized SnO2. Additionally, gas sensitivity towards ethanol for the synthesized SnO2 structures were tested. Formation of nanoparticles, rod-cluster structures and spherical SnO2 structures were observed depending on the synthesis conditions and synthesis starting solution used. Morphology of the synthesized structures greatly affected their sensitivity towards ethanol vapor. |
| 17:30 | X-Ray Photoelectron Spectroscopy of Electric Field Controlled Interface Effects in Multiferroic Tunnel Junctions ABSTRACT. S. Majumdar1, G. Sinha1, J. Lahtinen2 and S. van Dijken1 1Nanospin, Dept. of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland. Coexisting tunnelling electroresistance (TER) and tunnelling magnetoresistance (TMR) effects in multiferroic tunnel junctions (MFTJ) is an emergent phenomena for nonvolatile, energy efficient memory components [1]. In an MFTJ, two ferromagnetic (FM) electrodes acting as spin polarizer and analyzer, respectively, are separated by an insulating ferroelectric (FE) barrier instead of the more traditional dielectric barrier in magnetic tunnel junctions. In an MFTJ, in addition to the bistable resistance states due to parallel (P) and antiparallel (AP) aligned FM electrodes, two more resistance states can be accessed by rotation of the FE polarization in the tunnel barrier. Therefore, MTFJs can retain four non-volatile resistance states. Moreover, owing to the coupling between FM and FE polarization at the interfaces of an MFTJ, the spin polarization of the tunneling electrons can be reversibly inverted by switching of the FE polarization in the barrier [2]. Large TER effect in MFTJs has often been explained by electric field induced modification of the electronic properties at the FM - FE interface either via charge accumulation/depletion [3] or ion migration [4]. In the current work, we investigate electric field induced electronic reconstruction at an interface between FM electrode La2/3Sr1/3MnO3 (LSMO) and FE layer P(VDF-TrFE) using X-ray photoelectron spectroscopy (XPS) [5]. Our measurements show that polarization switching in ultrathin organic FE film modulates the Mn valence state at the LSMO-P(VDF-TrFE) interface that in turn can induce large change in magnetic and transport properties at the LSMO interface. After removal of the bias, the induced electronic effects partially remain for more than 24 hours. Additional measurements on temperature dependent relaxation of the electronic states after the removal of electric field is underway that will give us a clear indication whether the modulation of Mn valence state is electronic or ionic in origin. [1] V. Garcia , M. Bibes , Nat. Commun. 5 (2014) 4289. [2] D. Pantel et al., Nat. Mater. 11 (2012) 289. [3] C. A. F. Vaz et al., Phys. Rev. Lett. 104 (2010) 127202. [4] Q. Qin et al., Adv. Mater. 28 (2016) 6852. [5] S. Majumdar et al., (under preparation). |
| 17:30 | The iron oxidation state effect on its dispersion in an Mg-Al- Si-O glass matrix ABSTRACT.
N.M. Ferreira1,2, A.V. Kovalevsky2, M.A. Valente1, F.M. Costa1 1i3N, Dep. Fisica, Universidade de Aveiro, Portugal In several works had been mentioned the system MgO-Al2O3-SiO2-FeOy as the electrolyte basis for the molten oxide electrolysis process, in order to obtain molten Fe from its oxides, been an advantage since this composition is already present as a slag in iron extractive metallurgy [1-6]. There are several papers studying the structural changes of iron oxides, with major impact on its properties (magnetic, optical, catalytic, etc.) and prospective technological applications [2-7], however, few works had been donned to study the impact of iron in the electrical and magnetic properties of this glass system [8-11]. In this case, redox conditions and temperature are likely to determine the contents of iron oxides and onset of crystalline phases in the quaternary system MgO-Al2O3-SiO2-FeOy [2-11]. In order to understand the effect of iron distribution and the ratio between (Fe2+/Fe3+) can provoke in relevant properties of the glass system, amorphous samples with different iron contents and oxidation states, were obtained using the laser floating zone (LFZ) method, due its high temperature gradient. The influence of Fe2+/Fe3+ on iron distribution and local environments in the glass was analyze by XRD, SEM/EDS, density and Raman spectroscopy. The conductivity and magnetic moment measurements showed effect how the iron interacted with the glass matrix. As the results show the type of iron cation introduced in glass matrix can affect the iron oxidation state and local environment detected on the glass and also the properties measured. [1] A. Allanore, Electrochim. Acta 110, 587-592, (2013) [2] D.R. Sadoway in K.C. Liddell, R. G. Bautista and R.J. Orth, The Minerals, Metals & Materials Society, pp.73-76, (1994) [3] S.X. Wang, L.M. Wang, R.C. Ewing, R.H. Doremus, J. Non-Cryst. Solids 238, 198-213, (1998) [4] I.H. Jung, S.A. Decterov, A.D. Pelton, Metall. Mater. Trans. B 35B, 877-889, (2004) [5] D. Wang, A.J. Gmitter, D.R. Sadoway, J. Electrochem. Soc. 158, E51-E54, (2011) [6] Z.H. Jiang, S.J. Li, Y. Li, Journal of Iron and Steel Research International 18, 14-17, (2011) [7] R. Kaindl, D.M. Többens, U. HaefeKer, Am. Mineral. 96, 1568–1574, (2011) [8] M.D. Ingram, Current Opinion in Solid State & Materials Science 2, 399-404; (1997) [9] N.M. Ferreira, A.V. Kovalevsky, M.A. Valente, J.C. Waerenborgh, J.R. Frade, F.M. Costa, J.Crystal Growth, in press, Available online 12 February 2016, DOI: 10.1016/j.jcrysgro.2016.01.039; [10] N.M. Ferreira, A.V. Kovalevsky, M.A. Valente, N.A. Sobolev, J.C. Waerenborgh, F.M. Costa, J.R. Frade, Ceramics International 42 (2016) 2693-2698, DOI: 10.1016/j.ceramint.2015.10.150; [11] N.M. Ferreira, A.V. Kovalevsky, J.C. Waerenborgh, M. Quevedo-Reyes, A.A. Timopheev, F.M. Costa, J.R. Frade, Journal of Alloys and Compounds 611 (2014) 57–64, DOI: 10.1016/j.jallcom.2014.05.118 |
| 17:30 | Highly Oriented Growth of Piezoelectric Thin Films on Silicon and glass using Two-dimensional Nanosheets as Growth Template Layer ABSTRACT. Evert P. Houwman, Minh D. Nguyen, Huiyu Yuan, Gertjan Koster, Johan E. ten Elshof, Guus Rijnders MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands Ca2Nb3O10 (CNOns) and Ti0.87O2 (TiOns) metal oxide nanosheets (ns) are used as a buffer layer for epitaxial growth of piezoelectric capacitor stacks on Si and Pt/Ti/SiO2/Si (Pt/Si) substrates, as well as on glass. Highly (001) and (110)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) films are obtained by utilizing CNOns and TiOns, respectively. The piezoelectric capacitors are characterized by polarization and piezoelectric hysteresis loops and by fatigue measurements. The devices fabricated with SrRuO3 top and bottom electrodes directly on nanosheets/Si, with a deposition recipe that creates dense films, have ferroelectric and piezoelectric properties well comparable with devices using more conventional oxide buffer layers (stacks), such as YSZ, CeO2/YSZ or SrTiO3 on Si. The devices grown on nanosheets/Pt/Si show significantly improved polarization fatigue, properties over those of similar devices grown directly on Pt/Si. The deposition of films deposited on nanosheet buffered glass was changed to obtain an open columnar film. By this feature the longitudinal piezoelectric coefficient d33 of the film is increased from the usual value of the order of 100 pm/V for dense films to a value as high as 356 pm/V, obtained for a 2 µm thick film. The differences in properties of the films are ascribed to differences in the crystalline structures and the density of the films. These results show a route towards the fabrication of single crystal piezoelectric thin films and devices with high quality, long-lifetime piezoelectric capacitor structures on non-perovskite and even non-crystalline substrates, such as glass or polished metal surfaces. |
| 17:30 | In-plane magnetic anisotropy studies of bi-axially strained La0.67Sr0.33MnO3 thin films by Magneto-Optical Kerr Magnetometry ABSTRACT. Sandeep Kumar Chaluvadi1, Paolo Perna2, Fernando Ajejas2, Julio Camarero 2,3, Stéphane Flament1 and Laurence Méchin1 1Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France Understanding and controlling the magnetic anisotropy (MA) in La0.67Sr0.33MnO3 (LSMO) thin films constitute an essential step towards the use of this material for applications such as magnetoresistive sensors. Here we investigated the in-plane MA in LSMO thin films grown by pulsed laser deposition on different substrates using room temperature angular dependent Vectorial Magneto-Optical Kerr Magnetometry (V-MOKE) [1,2]. Since strain engineering is an effective tool to alter the properties of correlated functional oxide perovskites thin films [3,4], the different substrates were chosen so that they can induce either in-plane compressive strain on LaAlO3 (001, -1.36%), NdGaO3 (110, -0.31%) and La0.3Sr0.7Al0.65Ta0.35O3 (001, -0.12%) or in-plane tensile strain on SrTiO3 (001, +0.82%), SrTiO3 buffered MgO (001, >0.82%) and MgO (001, +8.04%). The epitaxial quality of films is tested by rocking curve analysis with FWHM around (002) peak of ~0.08° for films on nearly matched substrate NGO (110) to ~1.4°on MgO (001) with large strain. The experimental data show that the MA symmetry landscape significantly changes depending upon the substrate induced in-plane strain and the film thickness. At low thickness, the dominant anisotropy is due to interface effects, octahedral rotations [5] and substrate texture. At intermediate thickness, and in particular for LSMO on LSAT (001) we envisage two main contributions for the anisotropy: (i) a strong bi-axial (four-fold symmetry) MA (with easy axes (e.a.) along <110>pc and <1-10 >pc crystallographic axes) due to cubic magneto-crystalline anisotropy, and (ii) a weak uniaxial (two-fold) MA due to orthorhombic crystal structure of LSMO (with e.a. along <100>pc). In general, for larger LSMO thickness on LSAT (001), the orthorhombicity dominates the cubic crystal anisotropy and presents a strong uniaxial MA with easy axis along <100>pc axes. In LSMO films grown onto STO (001), the MA presents a competition between (four fold) magnetocrystalline and (one-fold) substrate step induced anisotropy. In the case of LSMO film grown on STO buffered MgO (001), a strong (four-fold) magnetocrystalline anisotropy observed along <110>pc and its equivalent pseudocubic axes. Comparing with all the cubic substrates, orthorhombic NGO (110) always exhibits a profound uniaxial anisotropy due to anisotropic stress along two in-plane directions with easy axis aligned with the direction of higher stress <1-10>pc. [1] P. Perna, C. Rodrigo, E. Jimenez, F.J. Teran, N. Mikuszeit, L. Méchin, J. Camarero, and R. Miranda, J. Appl. Phys. 110, 0 (2011). [2] P. Perna, L. Mechin, M. Saib, J. Camarero, and S. Flament, New J. Phys. 12, (2010). [3] A. Vailionis, H. Boschker, W. Siemons, E.P. Houwman, D.H.A. Blank, G. Rijnders, and G. Koster, Phys. Rev. B 83, 064101 (2011). [4] C. Adamo, X. Ke, H.Q. Wang, H.L. Xin, T. Heeg, M.E. Hawley, W. Zander, J. Schubert, P. Schiffer, D. a. Muller, L. Maritato, and D.G. Schlom, Appl. Phys. Lett. 95, 112504 (2009). [5] Z. Liao, M. Huijben, Z. Zhong, N. Gauquelin, S. Macke, R.J. Green, S. van Aert, J. Verbeeck, G. Van Tendeloo, K. Held, G.A. Sawatzky, G. Koster, and G. Rijnders, Nat. Mater. 1 (2016). |
| 17:30 | Relation between properties and structure in Ba(Sn,Ti)O3 photoferroelectric solid solutions ABSTRACT. H. Volkova, P. Gemeiner, P. Nukala, F. Karolak, C. Bogicevic, B. Dkhil and I.C. Infante SPMS Lab, UMR8580 CNRS & CentraleSupélec, Université Paris-Saclay, Grande Voie des Vignes, Chatenay-Malabry 92290, France halyna.volkova@centralesupelec.fr Ferroelectric solid solutions offer a possibility for engineering functional properties, for instance in the framework of photoferroelectrics the optical properties can vary in non-monotonous manner [1,2]. Understanding these variations and gaining control over them could enable the creation of new and more efficient devices integrating these photosensitive materials, and in particular in the fields of photovoltaics or photocatalysis. In this work, we focus on BaTiO3-based systems, since it is an environmentally friendly ferroelectric and cheap to produce. Based on ferroelectric BaTiO3 and paraelectric BaSnO3, we have synthesized Ba(SnxTi1-x)O3 solid solutions [3,4], prepared as bulk powders and we have also explored their synthesis in thin film form. BaSnO3 was chosen due to the presence of Sn 5s 5p orbitals in its conduction band [5], which could contribute to increase electron mobility in solid solutions. In addition to measuring dielectric properties, we have performed Raman spectroscopy and a study of optical properties using UV-visible spectroscopy. We have noticed a significant increase of the band gap (>0.3 eV) for x = 0.8 compared to the pure BaTiO3 that we propose to explain through a detailed analysis of the spectroscopy data and in view of the changes in the local chemistry and polar properties of these compounds. [1] Paillard C. et al., Adv. Mat. 28(26), 5153-5168 (2016) [2] R. Nechache, C. Harnagea, S. Li et al., Nat. Photon., 9(1), 61-67 (2015) [3] C. Lei, A. A. Bokov, and Z.-G. Ye, J. App. Phys, 101, 084105 (2007) [4] V. V. Shvartsman,a W. Kleemann, and J. Dec et al., J. App. Phys, 99, 124111 (2006) [5] Bog G. Kim, J.Y. Jo, S.W. Cheong, Journal of Solid State Chemistry 197, 134–138 (2013) |
| 17:30 | Polarisation effect on tunnelling magnetoresistance in artificial multiferroic tunnel junctions ABSTRACT. Geanina Apachitei, Marin Alexe University of Warwick, Physics Departments, Gibbet Hill Road, CV4 7AL, Coventry, United Kingdom In metal/insulator/metal junctions under certain conditions tunneling processes can occur leading to a measurable tunneling current. This current can be tuned by using functional materials such as ferromagnetic electrodes and ferroelectric barriers in magnetic tunnel junctions and ferroelectric tunnel junctions, respectively with applications in data storage devices. During the attempt to obtain reliable 4-state non-volatile devices by combining the two order parameters, interfaces with multiferroic behavior were obtained which are not completely understood. In La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3/Co tunnel junctions a change in the tunneling magnetoresistance sign was observed with switching the ferroelectric polarization of the barrier. Attention was directed towards the induced magnetic moment of interfacial Ti ions by Co in tunnel junctions containing PbZr0.2Ti0.8O3 and PbTiO3, but this does not fully explain the effect. Moreover, no experimental investigations were performed on the contribution of the Zr ions. The aim of this work is to investigate devices with PbTiO3, PbZrO3 and PbZr0.2Ti0.8O3 barriers in order to understand the contribution of Zr and Ti ions displacement on the spin polarisation. |
| 17:30 | Facile preparation of MnO2-polyaniline composite by plasma method and its biosensor application ABSTRACT. Sadik Cogal1, Gamze Celik Cogal2, Aysegul Oksuz2 1Mehmet Akif Ersoy University Faculty of Engineering and Architecture Department of Polymer Engineering, Burdur, Turkey Manganese dioxide (MnO2) is an important transition metal oxide with excellent physicochemical properties and has been found wide applications including catalysis, biosensor, and energy storage [1-2]. Conducting polymers (CPs) such as polythiophene, polypyrrole and polyaniline have been widely investigated materials because of their unique properties. Among the CPs, polyaniline (PANI) is one of the most extensively studied due to its environmental stability, processability, ease of synthesis, interesting redox properties, and low cost [3]. Composite materials have been attracted particular attention and exhibited better properties due to the synergic properties and functionalities of the components. The development of MnO2 and polyaniline composites was reported and generally used for capacitor applications. However, very few reports are available about the biosensor applications. In this study, MnO2/polyaniline composite was prepared by using RF-rotating plasma (produced with a frequency of 13.56 MHz at 40 W). In order to obtain homogenous coating on MnO2 surface, vapors of polyaniline monomer were slowly flowed through the plasma chamber, which was rotated at a constant rate during the experiment. The obtained composite was used without further purification and characterized in terms of morphological, structural, spectroscopic and thermal gravimetric analysis. The MnO2/PANI composite was then used to modify the glassy carbon electrode for amperometric biosensor application. [1] X. Wang, Y. Li. J Am Chem Soc 124, 2880, 2002. [2] Y.L. Luo. Mater Lett 61, 1893, 2007. [3] S. Bhadra, D. Khastgir, N.K. Singha, J.H. Lee. Prog Polym Sci 34, 783-810, 2009. This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK; Project no. 114M867), by bilateral project SAS- TÜBİTAK JRP 2014/2 and TUBITAK/COST (Project No. 114M877). |
| 17:30 | Epitaxial integration of oxides on Si with native oxide ABSTRACT. D. Dubbink, G. Koster, G. Rijnders MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands Growth procedures to integrate epitaxial oxides on silicon often require ultra-high vacuum conditions due to the need to handle reactive silicon surfaces. Less demanding conditions would be beneficial from an industrial point of view. In this work, methods were investigated to grow directly on the silicon native oxide, thereby avoiding reactive surfaces and chemical etching steps. In order to find suitable growth procedures, knowledge about the chemical interactions between metal oxides and silicon is necessary, as well as insights in the possibilities to control the chemistry during the growth process. Chemistry and growth of several metal oxides were investigated in this work. The fluorite yttria stabilized zirconia (YSZ) and perovskite SrZrO3 were studied because of the oxygen scavenging capabilities of Zr. During growth in reducing conditions, Zr breaks down the native oxide, after which epitaxial crystallization can occur. Furthermore, the mechanism of SrO assisted silicon deoxidation was elucidated by X-ray Photoelectron Spectroscopy (XPS) experiments. Controlled deoxidation resulted in stable strontium silicate templates which were suitable for crystallization of epitaxial perovskites. All experiments were performed in a Pulsed Laser Deposition system with in situ XPS, Reflection High-Energy Electron Diffraction and plasma spectroscopy. The authors thank the Dutch technology foundation STW for financial support (HTSM project no. 12790). |
| 17:30 | Domain walls oscillations in piezoelectric ceramics ABSTRACT. E. Buixaderas1, V. Bovtun1, M. Kempa1, D. Nuzhnyy1, M. Savinov1, P. Vanek1, B. Malic2 1Institute of Physics, Czech Academy of Sciences, Na Slovance 2 182 21 Prague 8, Czech Republic It is known for a long time that one of the main contributions to the dielectric response of piezoelectric ceramics is lying in the GHz range [1]. Ceramics and single crystals of the most famous piezoelectric materials – Pb(Zr,Ti)O3 (PZT), BaTiO3, LiNbO3 – show a broad relaxation in the frequencies 108-1010 Hz. The origin of this broad and strong excitation has been studied for these ceramics, and related to acoustic emission of domain walls, but is was never studied in a broad temperature range to be related to any dielectric anomaly present in the dielectric measurements. In this work, the temperature dependences of the terahertz and high microwave excitations of morphotropic PZT 52/48 ceramics were studied by a broad-band spectroscopy approach, using far infrared, time-domain THz and dielectric spectroscopies, including the coaxial technique in the microwave (MW) range. MW excitations are usually attributed to the contributions of piezoresonances in grains and of domain wall oscillations. In our case two contributions were found in the asymmetric excitation in the GHz range, which displayed a softening towards 270 K, in agreement with a maximum in the low frequency dielectric loss spectra. One contribution, with constant frequency, was assigned to piezoelectric resonances in grains and the soft one was related to domain wall oscillations. Together, both explain satisfactorily the dielectric anomaly of morphotropic PZT below room temperature, without taking into account another transition to a lower symmetry phase, therefore they show the extrinsic character of this dielectric anomaly. |
| 17:30 | First-principles investigation of ferroelectric nano-domains ABSTRACT. M.A.P. Gonçalves1, P. García-Fernández2, J. Junquera2 and J. Íñiguez1 1Materials Research and Technology Department, Luxembourg Institute of Science and Technology (LIST), 41 rue du Brill, L-4422 Belvaux, Luxembourg Nowadays, ferroelectric domain walls offer intriguing possibilities for progress in nano-science and nano-technology, as they present a variety of properties -- from conductivity and optical to magnetic -- that differ from those characterizing the domains themselves [1]. In particular, the domain walls can present structural transitions and functional properties (switchable orders) of their own, as recently evidenced by an investigation of PbTiO3 [2] using first-principles-based model potentials and large-scale lattice-dynamical simulations [3]. Using these techniques, we are now investigating the behavior of ferroelectric nano-domains immersed in a big domain of opposite polarization. Our results show states characterized by exotic dipoles orders with different arrangements of vortices and anti-vortices, revealing states of skyrmionic nature. We have also found that these dipole structures can be controlled by modifying the shape and the strain of the nano-domain, which may open the door to interesting physics and applications. In this poster we will summarize our most interesting results so far. [1] G. Catalan, J. Seidel, R. Ramesh, and J.F. Scott, Rev. Mod. Phys. 84, 119 (2012). [2] J.C. Wojdeł and J. Íñiguez, Phys. Rev. Lett. 112, 247603 (2014). [3] J.C. Wojdeł, P. Hermet, M.P. Ljungberg, P. Ghosez, and J. Íñiguez, J. Phys.: Condens. Matter 25, 305401 (2013). |
| 17:30 | The electronic structure of (strained) LaCoO3 from polarization and angular dependent 2p3d resonant inelastic X-ray scattering ABSTRACT. Ru-Pan Wang1*, Jaap Geessinck2, Gertjan. Koster2, K. Tomiyasu3, J. Okamoto4, Wen-Bin Wu4, Di-Jing Huang4, F.M.F. de Groot1 1Inorganic Chemistry & Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, The Netherlands LaCoO3 shows no magnetic order below 35K but paramagnetism above 120K [1]. In addition, a distortion or extra charges implies the system changes from non-magnetic to ferromagnetic [2]. The understanding of ground state electronic structure of the LaCoO3 in both bulk and strained thin films is important for new spintronic devices, where we note that there are a number of alternative explanations [3-5]. 2p3d Resonant Inelastic X-ray Scattering (RIXS) involves a 3d6 > 2p53d7 > 3d6 transition (+ plus charge transfer). The recent improvement of energy resolution implies that we can investigate the dd excitations and spin excitations better [6-8]. 2p3d RIXS can distinguish the d-states and spin states within the 3d6 manifold with the selection rules in different polarization and (sample and detection) geometry [9]. In this work we present the 2p3d RIXS spectrum on LaCoO3 single crystal and LaCoO3 thin films grown on (001)-SrTiO3 and (001)-LaAlO3 with a thickness of 60 nm. The result shows clear polarization and angular changes as a function of the distortion effect. [1] J.-Q. Yan et al., Phys. Rev. B. 69, 134409 (2004) [2] D. Fuchs et al., Phys. Rev. B 75, 144402 (2007); Phys. Rev. B. 77, 014434 (2008) [3] J. F. Afonso et al., arXiv: 1612.07576 [4] A. Ishikawa et al., Phys. Rev. Lett. 93, 136401 (2004) [5] Z. Ropka et al., Phys. Rev. B 67, 172401 (2003) [6] G. Ghiringhenlli et al., Phys. Rev. Lett. 102, 027401 (2009) [7] M. M. van Schooneveld et al., J. Phys. Chem. C 16, 15218 (2012) [8] M. Matsubara et al., J. Phys. Soc. Jpn. 74, No. 7 (2005) [9] M. van Veenendaal et al., Phys. Rev. Lett. 96, 117504 (2006) |
| 17:30 | Control of High Quality SrVO3 Electrode in Oxidizing Atmosphere ABSTRACT. B. Berini1, V. Demange2, M. Bouttemy3, E. Popova1, N. Keller1, Y. Dumont1 and A. Fouchet1,4 1GEMaC (UMR 8635) UVSQ - CNRS, 45 Av. des États-Unis; 78035 Versailles; France Arnaud.fouchet@ensicaen.fr, Bruno.berini@uvsq.fr Transition metal oxides with the perovskite structure attract a growing interest due to their exceptionally broad range of functionalities arising from the complex interplay between charge, orbital, spin and lattice degrees of freedom and controllable by external stimuli. This opens the way for oxide electronics (oxytronics) [1]. Among perovskites, strontium vanadate SrVO3 (SVO) is a model material for the study of strongly correlated systems due to his relative simple cubic structure with only one electron per vanadium and his electronic properties [2]. He is in the heart of fundamental research for studying the Metal Insulator Transition [3] and promising as solid oxide fuel cell anode [4], as electrode in all oxide epitaxial heterostructure [5] and used as transparent conductor [6]. Nevertheless, SrVO3 is sensitive to oxygen atmosphere and V4+ has the tendancy to dismutation [7]. Therefore, the oxygen stability and its influence on morphology and electrical properties of SrVO3 grown by pulsed laser deposition onto SrTiO3(100) has been investigated. Indeed, films grown at low oxygen pressure exhibit a very smooth surface while increasing roughness and the appearance of the crystallites at the surface have been evidenced for the films grown under higher oxygen pressure. Resistivity measurements show that low pressure deposition decreases the conductivity of SVO, mainly due to apparition of oxygen vacancies. Subsequent thermal treatments have been performed to prevent this secondary phase from forming and improve the transport properties. These results show that to obtain high quality SVO films with controllable electrical properties, it is essential to take into account the extreme sensitivity of SVO to oxygen during the growth process and post-growth thermal treatment [8]. [1] P. Zubko et al. , Annu. Rev. Condens. Matter Phys., vol. 2, no 1, p. 141-165, 2011. [2] S. Backes et al., Phys. Rev. B, vol. 94, no 24, déc. 2016. [3] K. Yoshimatsu et al., Phys. Rev. Lett., vol. 104, no 14, p. 147601, avril 2010. [4] A. A. Yaremchenko et al., Solid State Ion., vol. 247–248, p. 86‑93, oct. 2013. [5] J. A. Moyer et al., Adv. Mater., vol. 25, no 26, p. 3578‑3582, juill. 2013. [6] L. Zhang et al., Nat. Mater., vol. 15, no 2, p. 204‑210, déc. 2015. [7] P. Dougier et al., J. Solid State Chem., vol. 15, no 2, p. 158‑166, oct. 1975. [8] B. Bérini et al., Adv. Mater. Interfaces, vol. 3, p. 1600274, juill. 2016. |
| 17:30 | Spin and lattice excitations in the room-temperature magnetoelectric (Ba0.2Sr0.8)3Co2Fe24O41 with Z-type hexaferrite structure ABSTRACT. F. Kadlec,1 C. Kadlec,1 F. Borodavka1, J. Vít,1 Rujun Tang,2 J. Buršík,4 V. Bovtun,1 M. Kempa,1V. Goian,1 and S. Kamba1 1 Institute of Physics, The Czech Academy of Sciences, Prague, Czech Republic (Ba0.2Sr0.8)3Co2Fe24O41 crystallizes in the hexagonal Z-type hexaferrite structure and, in external magnetic field, it belongs to a rare group of room-temperature multiferroics. THz, Raman, microwave and infrared spectra of its ceramics were measured in a broad range of temperatures. Two sharp modes, corresponding to spin excitations, were observed, with frequencies and damping depending on the temperature and magnetic field. Another resonance was observed in zero-field microwave spectra; this mode emerges in the THz range upon applying a strong magnetic field. We interpret this mode as the ferromagnetic resonance which might play a role of a soft magnon mode, driving the multiferroic phase transition at 500 K. |
| 17:30 | Modulating the ferromagnet/molecule spin hybridization using an artificial magnetoelectric ABSTRACT. Martin Bowen1, Michał Studniarek1,4, Salia Cherifi-Hertel1, Etienne Urbain1, Ufuk Halisdemir1, Rémi Arras5, Beata Taudul1, Filip Schleicher1, Marie Hervé3, Charles-Henri Lambert2, Abbass Hamadeh2, Loïc Joly1, Fabrice Scheurer1, Guy Schmerber1, Victor Da Costa1, Olivia Mauguin6, Ludovic Largeau6, Florian Leduc4, Fadi Choueikani4, Edwige Otero4, Wulf Wulfhekel3, Jacek Arabski1, Philippe Ohresser4, Wolfgang Weber1, Eric Beaurepaire1, Samy Boukari1 1Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, F-67000 Strasbourg, France Spin-polarized charge transfer at the interface between a ferromagnetic metal and a molecule can lead to ferromagnetic coupling [1] and to a high spin polarization [2] at room temperature [3-4]. The magnetic properties of these interfaces can not only alter those of the ferromagnet [5], but can also stabilize molecular spin chains [6-7] with interesting opportunities toward quantum computing. With the aim to enhance an organic spintronic device’s functionality [8], an external control over this spin polarization may thus be achieved by altering the ferromagnet/molecule interface’s magnetic properties. To do so, we utilize the magnetoelectric properties [9] of an underlying ferroelectric/ferromagnetic interface. Switching the ferroelectric polarization state of a PbZr0.2Ti0.8O3 (PZT) bottom layer within a PZT/Co/FePc-based device alters the X-ray-magnetic circular dichroism of the Fe site within the phthalocyanine (Pc) molecular top-layer. We thus demonstrate how to alter the magnetic properties of an interface with high spin polarization at room temperature [4]. This expands electrical control over spin-polarized FM/molecule interfaces, which was first demonstrated using ferroelectric molecules [10], to all molecular classes. [1] A. Scheybal et al Chem. Phys. Lett. 2005, 411, 214. [2] C. Barraud et al, Nat. Phys. 2010, 6, 615. [3] S. Lach et al, Adv. Funct. Mater. 2012, 22, 989. [4] F. Djeghloul et al, Sci. Rep. 2013, 3, 1272. [5] K. V. Raman et al Nature 2013, 493, 509. [6] M. Gruber et al Nat. Mater. 2015, 14, 981. [7] C. Barraud et al Phys. Rev. Lett. 2015, 114, 206603. [8] S. Sanvito, V. A. Dediu, Nat. Nanotechnol. 2012, 7, 696. [9] O. Vlašín et al, ACS Appl. Mater. Interfaces 2016, 11, 7553. [10] S. Liang et al, Adv. Mater. 2016, 28 1521. |
| 17:30 | Photocatalytic properties of TiO2 thin films doped with noble metals (Ag, Au, Pd and Pt) ABSTRACT. George A. Mousdis1, Cherif Moslah2, Maria Kandyla1, Muhammad Monirul Islam3, and Mohamed Ksibi2 1Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation,48 Vassileos Constantinou Ave. 11635,Athens, Greece Titania (TiO2) nanomaterials are the most promising photocatalysts for the degradation of organic pollutants in water. In particular, TiO2 thin films have attracted great interest, due to their versatility and scalability. However, for practical applications, TiO2 photocatalysts have two main disadvantages: low quantum efficiency and operation only for short wavelength excitation. To overcome these problems, a lot of work has been devoted to improve the photoactivity of TiO2 by doping with transition and noble metals. In this work, sol-gel grown TiO2 thin films were deposited on glass substrates by spin-coating, using noble metals (M= Ag, Au, Pd and Pt) for doping. The films were thermally treated at 500 °C, to obtain the anatase phase. The film properties were characterized by X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectrometry, profilometry and UV/VIS spectroscopy. Optical measurements showed a narrower optical band gap (Eg) for all noble metal-doped TiO2 films (M-TiO2), in comparison to pure TiO2. The photocatalytic activity of all films was evaluated by measuring the rate of decolorization of Methylene Blue (MB) under UV irradiation. All films showed significant photocatalytic activity and the 1 mol% Pd-TiO2 film showed the best performance. |
| 17:30 | Ordering and phase control in epitaxial (Pr,Ba)CoO3-d catalysts for oxygen evolution reaction ABSTRACT. Felix Gunkel1, Lei Jin2, David N. Müller3, Clemens Hausner1, Daniel Bick1, Chunlin Jia2, Theodor Schneller1, Rainer Waser1,3, Ilia Valov1, and Regina Dittmann3 1Institute of Electronic Materials (IWE2) RWTH Aachen University, Aachen, Germany The complex oxide compound (Pr0.5Ba0.5)CoO3−d (PBCO) is considered an efficient catalytic oxide for oxygen evolution half-reaction (OER) taking place during water splitting operation. We discuss structural and electrical properties of epitaxial PBCO thin films serving a model systems for exploring the atomistic processes during OER. PBCO thin films are synthesized in a disordered and in an ordered double-perovskite crystal structure by controlling the growth temperature during pulsed laser deposition. The thin films are fabricated with defined surface morphologies and crystal orientation. During the growth process, the transition from disordered to ordered phase can be monitored directly by means of electron diffraction (RHEED). The epitaxial thin films show catalytic activity comparable to their porous counter parts fabricated by chemical routes, making them ideal model templates for systematic studies. We find similar catalytic properties for samples grown in ordered and disordered fashion, indicating a negligible effect of the structural bulk phase on OER catalysis. Instead, both phases, ordered and disorder perovskite provide a comparable surface landscape catalyzing OER. |
| 17:30 | Magnetoelectric coupling in multiferroic BiMnO3 thin films ABSTRACT. G. De Luca Dipartimento di Fisica E. Pancini, Università degli Studi di Napoli Federico II In the last years, the development of systems employing particles or quasi particles as information carriers with zero dissipation is attracting big interest inside the scientific community. In this framework, the physicists are pointing their attention on multiferroic magneto-electric (ME) materials, considered now the key materials of new dissipationless electronics. Indeed, ME effect has attracted, since the beginning, a large interest due to the cross coupling between magnetic properties and electric field: it is possible to control the magnetic properties by an electric field and vice-versa, realizing devices with minimal power consumption and low cost. In this seminar, it will be shown first results on ME coupling in multiferroic BiMnO3 thin films [1], using XMCD, XMLD and XLD synchrotron based techniques. [1] De Luca G. M. et al. Ferromagnetism and ferroelectricity in epitaxial BiMnO3 ultra-thin films, Appl. Phys. Lett.103, 062902 (2013) |
| 17:30 | Quartz crystal microbalance technique for detection of NO2 ABSTRACT. I. Nedkov Institute of Electronics, Bulgarian Academy of Sciences The new results and experiences in the technology and sensing characteristics of the ZnO nanostructured (NS) films- and TiO2 films - Quartz Crystal Microbalance (QCM) structures are the object of this presentation. The sensitivity of the QCM technique make rapid progress in the last years, because of the high accuracy and rapidity. ZnO and TiO2 films were deposited on both sides of a 16-MHz QCM. The surface morphology of the films was examined by scanning electron microscopy, Raman spectroscopy and the surface composition was determined by X-ray photoelectron spectroscopy. Sorption properties of layers were defined by measuring the resonant frequency shift (Δf) of the QCM-ZnO or TiO2-QCM structures for different NO2 concentrations. The measurements were based on the correlation between the frequency shift of the QCM and additional mass loading (Δm) on the resonator calculated using Sauerbrey equation for the AT-cut quartz plate. Frequency – Time Characteristics (FTCs) of the samples were measured as a function of different NO2 concentrations in order to define the sorption abilities of ZnO layers. The experiments were carried out on a special set up in a dynamical regime. From FTCs the response and the recovery times of the QCM-ZnO structure were measured with varying NO2. Frequency shift changed from 23 Hz to 58 Hz when NO2 was varied in the range of 250 ppm – 5000 ppm. The process of sorption was estimated as reversible and the sorption as physical. The obtained results demonstrated that QCM covered with the electrochemically deposited nanostructured ZnO films can be used as application in NO2 sensors. The TiO2 films were tested in the NO2 concentration interval from 10 ppm to 5000 ppm. It was found that a TiO2 loading of the QCM by 5.76 kHz corresponded to a system sensitive to NO2 concentrations above 250 ppm. On the basis of the FTCs measured, ΔF at different NO2 concentrations was defined, the adsorption/desorption cycles were studied and the response and recovery times were estimated. Results obtained show that a processes in the two investigated structures were reversible for NO2 in large range of concentrations and suggested that ZnO NS and TiO2 films combined with QCM technique are suitable as a sensor element for NO2 detection. |
| 17:30 | Superconductor insulator transition in LaTiO3/SrTiO3 ABSTRACT. N. Lebedev1, M. Stehno2, A. Rana2, A. Brinkman2, G. Koster2 and J. Aarts1 1Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands At the interface between the antiferromagnetic Mott insulator LaTiO3 (LTO) and the nonmagnetic band insulator SrTiO3 (STO) a superconducting two-dimensional electron gas (2DEG) can form. Main focus of this work are transport properties of LTO/STO versus back gate. Samples are prepared by Pulsed Laser Deposition. The transport measurements show that the interfaces are conducting with a minimum of sheet resistance around 40 K at negative gate voltages. By gate-tuning, the Hall resistance changes from linear to nonlinear at low temperatures. Such behavior indicates the presence of two types of carriers in the gate range above -70 V. At temperatures below 0.3 K, we observe a superconductor-insulator transition. The intriguing part of this experiment is a significant shift to negative gate voltages in comparison to previous reports [1]. Additionally we observe negative magnetoresistance at large negative gate voltages in perpendicular field configuration. The transport measurements with in-plane field geometry also show negative magnetoresistance at 3 K for whole range of applied gate bias. Work performed in the framework of the FOM-program DESCO. [1] J. Biscaras et al, PRL 108, 247004 (2012); DOI: 10.1103/PhysRevLett.108.247004 |
| 17:30 | Puzzling Conductivity Variations in Nominally-Undoped beta-Ga2O3 Thin Films ABSTRACT. E. Chikoidze1, Y. Dumont1, D. J. Rogers2, F. H. Teherani2, V. E. Sandana2, P. Bove2, T. T. Huynh3, L. L. C. Lem3, M. R. Phillips3 and C. Ton-That3 1Groupe d’Etude de la Matière Condensée (GEMaC), UVSQ – CNRS, Université Paris-Saclay, Versailles, France Conventional transparent conductive oxides (TCO) such as ITO and AZO are opaque in the UVB and UVC spectral ranges, due to their relatively small energy band gap <3.5 eV, and new TCO materials need to be explored for this purpose [1]. One such material is Ga2O3. With an optical bandgap of 4.8-5 eV it has attracted strong interest for various applications including transparent electrodes, thin film transistors, UVC sensors and LEDs [2-4]. Our work is dedicated to Ga2O3 , in the beta-phase, which is one of the five known phases and is recognised as being one of the most stable [5]. Nominally undoped ß-Ga2O3 thin films were deposited on sapphire substrates (of various orientations) using Pulsed Laser Deposition in molecular oxygen with a KrF excimer laser and a commercial 5N sintered Ga2O3 target. Highly (-201) oriented beta-Ga2O3 layers were obtained on c-, a- and r-plane sapphire. Optical transmission studies revealed high transparency (>80%) from the NIR right through to the UVC region of the spectrum and bandgaps of between 5.0 and 5.5 eV. Cathodoluminescence (CL) revealed a broad UV band peaked at 3.8 eV at room temperature. A second blue luminescence peak emerged at 3.0 eV in CL spectra acquired at 80 K. Both insulating and intrinsicly conductive layers were obtained by varying the growth temperature and oxygen partial pressure. [1] M. Orita, H. Ohta, M. Hirano, and H. Hosono: Appl. Phys. Lett. 77 (2000) 4166. [2] N. Suzuki, S. Ohira, M. Tanaka, T. Sugawara, K. Nakajima, and T. Shishido: Phys. Status Solidi C 4 (2007) 2310. [3] K. Matsuzaki, H. Yanagi, T. Kamiya, H. Hiramatsu, K. Nomura, M. K. Matsuzaki, H. Yanagi, T. Kamiya, H. Hiramatsu, K. Nomura, M. Hirano, and H. Hosono: Appl. Phys. Lett. 88 (2006) 092106 [4] T. Oshima, T. Okuno, and S. Fujita: Jpn. J. Appl. Phys. 46 (2007) 7217. [5] R. Roy, V. G. Hill, and E. F. Osborn: J. Am. Chem. Soc. 74 (1952) 719. |
| 17:30 | First-principles investigation of ferroelectricity in layered perovskite oxide Sr2Nb2O7 ABSTRACT. Javier Alanis1, Jorge Íñiguez2 1Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo, Postal J-48, Puebla, Pue. 72570, México. Layered perovskite oxide Sr2Nb2O7 (SNO) is a good candidate for high temperature piezoelectric applications due to its high Curie temperature (1610 K) [1]. SNO is a member of the pyrochlore family whose structure can be see as a perovskite periodically truncated along the [011] pseudo-cubic direction. The spontaneous polarization in SNO emerges essentially from the rotations of the O6 octahedra [2], and not from the movement of the A or B cations, as usual in ideal ABO3 perovskite structures [3]. This O6 octahedra rotations can be modulated [4] and may therefore be useful in the design of multiferroic materials [3]. We are investigating the structural instabilities and ferroelectric phases of SNO and related compounds using first-principles methods, adapting the theoretical approach that King-Smith and Vanderbilt [5] first introduced for simple perovskite oxides. In this poster we will present the results obtained thus far. [1] H. Ning, H. Yan, and M. J. Reece, J. Am. Chem. Soc. 93 1407 (2010). [2] P. Daniels, R. Tamazyan, C. A. Kuntscher, et. Al., Acta Cryst. B58, 1912 (2002). [3] J. López-Pérez and J. Íñiguez, Phys. Rev. B 84, 075121 (2011). [4] C. A. Kuntscher, S. Gerhold, N. Nücker, et. Al., Phys. Rev. B 61, 1876 (2000). [5] R. D. King-Smith and D. Vanderbilt, Phys. Rev. B 49, 5828 (1993). |
| 17:30 | Influence of temperature on structure and properties of lead titanate and bistmuth titanate films ABSTRACT. L. Marcinauskas, A. Iljinas, V. Stankus Department of Physics, Kaunas University of Technology, Studentu str. 50, LT-51368 Kaunas, Lithuania Thin films of lead titanate and bistmuth titanate have a great interesting and perspectives in application in electronics devices, such as: pyroelectric infrared detectors, capacitors, ultrasonic transducers, thermistors, optoelectronics, microsensors and actuators [1-2]. The most perspective applications of lead titanate and bismuth titanate are used in ultra-fast, very dense and non-volatile memory application (FRAM) [3-4]. Bismuth titanate and lead titanate thin films were deposited on heated platinized silicon substrates (400-550°C) using in situ layer-by-layer reactive DC magnetron sputtering. The thickness was determined using Linnic micro-interferometer and tested with profilometer and SEM cross-section. The surface morphology of the films was analyzed using scanning electron microscope. The crystallographic structure of thin films was investigated by X-ray diffraction. Sawyer and Tower method for polarization–electric field (P-E) loop measurements was used for hysteresis loops measurements. The results indicated that the surface morphology, structure and ferroelectric properties strongly depend on the formation temperature. Variation of the temperature allows to control the structure of the films and obtain the films with the highest ferroelectric properties. Hysteresis measurements showed that the highest coercive field of 150 kV/cm and the remnant polarization of 60 μC/cm2 were reached for the lead titanate film produced at the 550 °C substrate temperature. The highest coercive field of 130 kV/cm and remnant polarization of 73 μC/cm2 was obtained for the bismuth titanate film deposited at 450 °C. [1] M.A. Khan et al., Acta Mater, 56 (2008) 2110. [2] M. Chen et al., Mater. Lett., 139 (2015) 325. [3] Fang B. et al.Materials Letters. 84 (2012) 913. [4] S. Zhao et al., Thin Solid Films, 570, Part B (2014) 351. |
| 17:30 | Electrical, optical and structural properties of ITO thin films deposited by reactive plasma assisted thermal evaporation ABSTRACT. A. Iljinas, L. Marcinauskas, P. Dolmantas, R. Ramanauskas, V. Marudinas Department of Physics, Kaunas University of Technology, Studentu str. 50, LT-51368 Kaunas, Lithuania Transparent and conductive layers are widely used for many microelectronics applications, such as transparent in the visible and near infrared regions electrical contacts electrodes in displays, heat able glass and thin films solar cells. Tin doped indium oxide (indium tin oxide, ITO) is a wide band gap n-type semiconductor (Eg=3.5–4.3 eV) with high transparency in the visible light wavelength range. ITO is one of the most investigated and used transparent conductive oxides due to the small electrical sheet resistance (5-1000 Ω/sq). The electro-optical and structural characteristics of the ITO films are strongly dependent on deposition method and parameters. In this study ITO thin films were deposited on soda lime glass substrates by reactive plasma assisted thermal evaporation in O2 gas environment (oxygen pressure of 4 Pa). Metallic In and Sn pieces (Kurt J. Lesker Company (of 99.999% purity)) were thermally melted in the molybdenum evaporation boat and used as the evaporated material. The formation of the films was done at 350 °C temperature substrates. The surface morphology of the samples was analyzed using scanning electron microscopy. The elemental compositions of the deposited ITO structures were measured by energy dispersive spectrometry. The crystallographic structure of thin films was investigated by X-ray diffraction. Sheet resistance and resistivity dependence on temperature of the films were measured by a four point probe technique. This dependence was used for calculation of band gap of ITO films. The transmittance and reflectance spectra of the films were measured at a normal incidence with UV–VIS–NIR spectrophotometer. The absorption edge of the transmittance spectra was analyzed using Tauc method and optical band gap (Eg) was determined. It was obtained that the ITO films with the porous and uniform surface morphology and columnar structure were formed. The films have a low resistivity of 16.9 ▼ 10-3 Ω cm (sheet resistance 211 Ω/sq) and a transparency above 80 % was obtained. The band gap values determined by Tauc method and by resistivity dependence on temperature were 3.4 eV and 3.5 eV, respectively. The XRD profile showed the polycrystalline structure of the films. |
| 17:30 | YBaCuO microbridges properties modification using low energy electrons ABSTRACT. M. Talacko1, Š. Chromik1, V. Štrbík1, M. Sojková1, M. Španková1, G. Jung2, G. Bareli2, C. Camerlingo3 1Institute of Electrical Engineering, SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovakia Effects of low energy 30 keV electron irradiation of superconducting YBa2Cu3O7-δ thin films have been investigated by means of transport and micro-Raman spectroscopy measurements. We have observed the changes in the electrical properties of the YBCO bridges after the electron irradiation, where the irradiation take place in two ways: over the whole YBCO bridge and by using the irradiated area accurately arranged into the transversal channels. The idea of this work is to achieve easy coherent vortex motion in the irradiated channels in the future. YBCO thin films were prepared on various substrates using a PLD deposition technique patterned into bridges and used for investigation of the electrical properties and micro-Raman spectroscopy measurements before and after low energy 30 keV electron irradiation. Depending on time duration of the electron fluency at the point of fluency 1020 electrons/cm2 the measurements of irradiated bridges show enhancement (60 min.) or restriction (15 min.) of the electrical properties. Raman investigation suggest that critical temperature increase is due to healing of broken CuO chains in irradiated films that results in increase of the carrier´s concentration in superconducting CuO2 planes. Besides that many processes induced by electron irradiation were observed as oxygen removal, both by thermal activation and kick-off processes, and ordering of chains enviroment by incident electrons. In the next step we investigated the ability to create multiple transversal channels placed in the YBCO bridges using low energy 30 keV electron irradiation. The irradiated area was arranged into the 0.5 µm narrow stripes periodically repeated with distances between the stripes 7.5 - 10 µm oriented transversal across the bridges with the aim to repress superconductivity in this channels. As the first results show it is not possible to observe any changes in electrical properties of YBCO bridges with 0.5 µm stripes wide after the electron irradiation. It could be caused by reason of exposure area diffusion to the bulk. Therefore, after increasing irradiation area width from 0.5 µm to 2 µm we observed depression of superconductivity properties. It seems that this modification process could lead to direct coherent vortex motion applications. There are various outstanding technical and physical effects necessary to solve as are for example electron beam track unreproducibility, substrate influence or substrate heating. |
| 17:30 | Band-gap engineering in KNbO3-BiMeO3 (Me=Mn, Fe, Co and Ni) ABSTRACT. Cristina Pascual-Gonzalez1, Giorgio Schileo2 and Antonio Feteira1 1Christian Doppler Laboratory for Advanced Ferroics, Materials Engineering and Research Institute, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, UK cristina.pascualgonzalez@student.shu.ac.uk Band-gap engineering of ferroelectrics such as KNbO3 allows us to explore several photoresponsive phenomena such as photovoltage, photostriction and photocatalysis. In order to exploit those phenomena in technological applications one should be able to tune the band-gap into the visible range. In this study, we investigated the impact of BiMeO3 (with Me= Mn, Fe, Co and Ni) doping on the structure, dielectric and optical properties of KNbO3. XRD data combined with Raman Spectroscopy was employed to monitor both the average and local crystal structure evolution with increasing BiMeO3 content. Band-gaps varying from 3.2 eV down to 2.2 eV were estimated from reflectivity data collected using a spectrometer with an integrating sphere. In-situ Raman spectroscopy analysis corroborated the polar nature of these materials over a wide temperature range. The ability to control the band-gap while maintaining the spontaneous polarisation makes KNbO3-BiMeO3 solid solutions interesting for photoinduced processes in a wide temperature range. |
| 17:30 | Impact of the microstructure on the functional properties of (Ba,Ca)(Ti,Zr)O3 ceramics ABSTRACT. Lavinia Curecheriu1, Maria Teresa Buscaglia2, Giovanna Canu2, Vincenzo Buscaglia2, Liliana Mitoseriu2 1Dielectrics, Ferroelectrics& Multiferroics Group, Departament of Physics, Al.I. Cuza University, 11 Bv. Carol I, 700506, Iasi, Romania One of the most promising BT-based materials for priezoelectric applications is the pseudobinary ferroelectric (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BCTZ) (x is the molarpercent of BCT). In the present paper, we present preparation and functional characterisation of Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics with grain size larger than 1 μm. The powders were prepared by the conventional solid-state route starting from fine precursor powders and calcined at 1000°C/4 hours. Dense ceramics (relative density above 94-98%) with different grain size were obtained by sintering the resulted powders at temperatures between 1400-1500°C for different times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2 μm for the samples sintered at 1400C/2h to 27 μm for the samples obtained at 1500°C/24h. The evolution of polar order and phase transitions with grain size has been studied using dielectric permittivity measurements at 1Hz- 1MHz between 25 and 150°C. The high field dielectric properties (dc-tunability) show a slight modification with grain size. The presented data provide a complete picture of the size effect dependence of functional properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics. Acknowledgment: This paper was performed during ECOST-STSM-MP1308-191116-081333. |
| 17:30 | Local electric imaging at the LaAlO3/SrTiO3 interface of tetragonal domains and field-induced ferroelectric twin walls in conducting SrTiO3 ABSTRACT. D. Kohlberger1, H. J. Harsan Ma1,2,3, S. Scharinger1, S. W. Zeng2,3, M. Lange1, A. Stöhr1, T. Venkatesan2,3,4, R. Kleiner1, J. F. Scott5, J. M. D. Coey3,6, D. Koelle1, Ariando2,3 1Physikalisches Institut and Center for Quantum Science in LISA+, Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany; daniel.kohlberger@uni-tuebingen.de We apply low-temperature scanning electron microscopy (LTSEM) [1], down to temperature T = 5 K to image electric transport properties of conducting SrTiO3 (STO) by detecting the beam-induced voltage change for current-biased samples. Insulating single crystal STO substrates with either (001) or (110) orientation have been made conducting by surface electronic reconstruction induced by an epitaxially grown thin film overlayer of the polar oxide LaAlO3 (LAO) to create a two-dimensional electron gas (2DEG) at the LAO/STO interface. On LAO/STO microbridges, defined by photolithography, we observe stripe-like LTSEM patterns below the cubic-to-tetragonal phase transition of STO (105 K). We associate these patterns with the presence of twin boundaries that show a beam-induced increase in conductivity. The nature of the twin boundaries is confirmed by calculating their intersection angles with the STO surface. By applying an electric field via side- or back gates, field-induced twin walls appear above a threshold field, and these twin walls appear to show field-induced electric ordering [2]. Such a mechanism may enable the controlled creation of high-density domain walls on the nanoscale, which could have important applications on domain-wall engineering [3] for high-density storage applications. [1] R. Gross, D. Koelle, Rep. Prog. Phys. 57, 651-741 (1994). [2] H. J. Harsan Ma et al., Phys. Rev. Lett. 116, 257601 (2016). [3] E.K.H. Salje, Phase Transitions 86, 2-14 (2013). |
| 17:30 | The pO2-dependent formation of a space charge layer in donor doped SrTiO3 probed by in-situ spectroscopy ABSTRACT. Michael Andrä Forschungszentrum Jülich, Germany In recent years donor doped strontium titanate (n-STO) has gained a lot of attention as model material for various applications, such as gas sensing or resistive switching. In addition, it is widely used as a quasi-metallic substrate material for functional all oxide electronic devices. For this purpose, n-STO is often referred to as a degenerate n-type semiconductor. However, recent research on n-STO also indicated the existence of a surface space charge layer. In this study, we investigated the electronic surface structure of n-STO thin films. 0.5 wt% Nb-doped STO homoepitaxial thin films were analyzed by in-situ near ambient pressure XPS at a temperature of 770 K and a pO2 which ranged from ultra high vacuum conditions up to 5 mbar. Upon exposure to O2 gas at elevated temperatures, we detected a rigid shift of up to 0.6 eV for the binding energies of all characteristic STO core level peaks and the valence band maximum. The rigid shift is attributed to a relative shift of the Fermi level towards the valence band due to a negative charge accumulation at the surface and hence, an electron depletion layer in the near surface area. The negative surface charge may be provided by the formation of cation vacancies or the formation of charged oxygen adsorbates at the surface. Our results clearly indicate a pO2-dependent surface space charge formation in donor doped STO under oxidizing conditions at temperatures as low as 770 K. |
| 17:30 | Defect Engineering Through Thermal Treatment in Non-Stoichiometric CuCrO2 Delafossite Thin Films Grown by Chemical Vapor Deposition ABSTRACT. Petru Lunca Popa Luxembourg Institute of Science and Technology, Materials Research and Technology department, 41 rue du Brill, 4422 Belvaux, Luxembourg In the field of transparent electronic many efforts are today focused in searching a p-type semiconductor, with properties matching those of n-type actual ones, i.e. transparency around 80% in the visible range and electrical conductivities up to 1000 S.cm-1. Such p-type materials open new perspective on various technological fields as flat screen displays, thin-film solar cells or transparent sensors. Among various p-type transparent conducting oxides, delafossite CuCrO2 is particularly studied due to highest values reported of conductivities for a given optical transparency. However, conductivity/transparency trade-off is still insufficient and the physico-chemical properties must be better understood. There is a scientific debate concerning the electrical transport mechanisms and the source of doping in delafossite materials. Progresses will be surely achieved once the answers on these two topics will be rigorously addressed.. In this work, we adopt a new strategy in order to contribute to these two important features by studying non-stoichiometric and highly conductive CuCrO2 delafossites films. We introduce the thermal treatment as a tool to manipulate defects and to furthermore analyse them. High temperature treatments allowed the tailoring of metastable acceptor states. Our results clearly evidence a change of transport mechanism upon thermal treatment. The electrical conductivity also drops dramatically in annealed samples while the overall stoichiometry seems to remain unaffected. These results allow us to formulate some reliable hypothesis on the doping source in highly conductive non-extrinsically doped CuCrO2 thin films. |
| 17:30 | Preparation and study of resistivity chemical sensors based on metal oxides with metal nanoparticles as catalysts ABSTRACT. G. A. Mousdis, M. Kompitsas, G. Petropoulou, M. Kandyla National Hellenic Research Foundation, Theoretical and Physical Chemistry Institute, 48 Vasileos Constantinou Avenue, 11635 Athens, Greece The cheapest and most common chemical gas sensors are those based on metal oxide resistivity change, due to common and cheap raw materials and the easiness of preparation and signal processing. Although there are still problems with the selectivity of the metal oxides sensors, this can be overcome by using an array of different sensors that correspond different to each analyst. The sensing properties of a metal oxide film depend on the surface roughness, porosity, crystallinity and some other factors, which differentiate for each preparation method. Moreover, the addition of noble nanoparticles on the surface of the films, improves the sensing properties of the films. For these reasons the preparation and study of new metal oxide sensors in order to understand the mechanism and their dependence from the different factors is essential. In this work metal oxide films of CuO and ZnO doped with noble metal particles or undoped were prepared by the sol-gel method and the dependence of the composition and the preparation conditions to their sensing properties was studied. |
| 17:30 | Efficient systematic scheme to construct second-principles lattice-dynamical models ABSTRACT. Carlos Escorihuela-Sayalero1, Jacek C. Wojdeł2 and Jorge Íñiguez1,2 1Luxembourg Institute of Science and Technology (LIST), avenue des Hauts-Fourneaux, L-4362 Esch/Alzette, Luxembourg First-principles calculations using density-functional theory (DFT) are a very useful tool to study materials properties in depth. However, the considerable computational cost of such calculations imposes a limitation in the size of the simulated systems; thus, studying complex situations involving large simulation boxes and statistical averages becomes often infeasible. Many solutions have been proposed for this problem, at the expense of losing accuracy and introducing approximations. In particular, Wojdel and collaborators [1] recently presented an atomistic approach to run lattice-dynamical simulations (electrons are not treated explicitly) aimed at retaining the accuracy of the DFT calculations while being computationally affordable. More specifically, they construct an interatomic potential that has the form of a Taylor expansion in terms of atomic displacements and cell strains, around a certain reference structure, and forced to be explicitly compliant with the acoustic sum rule. The potentials thus constructed are systematically improvable and can in principle reproduce exactly the DFT potential energy surface, and the main technical difficulty is to find a way to compute the model parameters in a manner that is as automatic as possible. Here we present an efficient and flexible methodology to build such models via an optimization problem [2]. Our approach employs a suitably chosen goal function that permits an analytic solution to problem of fitting the potential parameters to a training set of DFT data; this very fast solution to the optimization problem allows us to explore the parameter space in an essentially complete way. We apply the method to construct models for ferroelastic perovskite strontium titanate as a test case. We show that our models reproduce the DFT-computed properties (ground state features, molecular-dynamics trajectories at various temperatures) very accurately, and allow us to simulate the structural phase transition in this compound. Further application of the models to different problems is shown to demonstrate their usefulness. [1] J. Wojdel et al., Journal of Physics: Condensed Matter 25, 305401 (2013) [2] C. Escorihuela-Sayalero et al., http://arxiv.org/abs/1608.06788 |
| 17:30 | Functional oxides on Silicon and Sapphire substrates for photonic applications ABSTRACT. Guillaume Marcaud, Sylvia Matzen, Carlos Alonso-Ramos, Xavier Le Roux, Mathias Berciano,Valérie Pillard, Pedro Damas, Thomas Maroutian, Guillaume Agnus, Ludovic Largeau, Eric Cassan, Delphine Marris-Morini, Philippe Lecoeur, Laurent Vivien C2N - Centre for Nanoscience and Nanotechnology, CNRS, University of Paris-Sud, University of Paris Saclay, Building 220, rue André Ampère 91405 Orsay cedex, France Silicon photonics is expected to address a wide range of applications including sensing, datacom and security with the potential to develop low-cost and complex circuits using silicon fabrication facilities. In this context, the hybrid integration of functional oxides on silicon photonic devices is a promising approach to bring other properties including multiferroicity, piezoelectricity, nonlinear optical properties in silicon photonics platform. Our work focuses on the integration of Yttria-Stabilized Zirconia (YSZ) functional oxide on sapphire substrates and on silicon. The common aim for both integrations is to induce nonlinear optical effects at the wavelength around 1550 nm, thanks to strain tuning in full oxide- or in hybrid oxide/Si- structures. This study includes the epitaxial growth of YSZ oxide thin layers by pulsed laser deposition technique (PLD) on silicon and sapphire substrates, their characterizations by several complementary techniques such as X-ray diffraction, AFM, SEM, TEM microscopies, and Raman spectroscopy, and also the fabrication and optical characterization of oxide-based photonic structures (gratings coupler and waveguides essentially). First, YSZ photonic structures were fabricated on sapphire substrates and characterized optically. We work on the optimization of the oxide growth (crystal quality and orientation) and fabrication processes to improve the optical transmission of YSZ. Then, YSZ was directly integrated on silicon substrate, to strain the Si lattice in order to study nonlinear optical properties of silicon. Indeed, the epitaxial growth of this oxide strains the silicon due to the difference of thermal expansion and the lattice mismatch. This can also play a role when YSZ is used as a buffer layer to integrate other functional oxides. We work on the growth of YSZ on silicon to improve the strain field applied to the photonic structures (measured with Raman spectroscopy) and their optical transmission. We will present and discuss our last results on the epitaxial growth of YSZ functional oxide by PLD on both sapphire and silicon substrates and on the fabrication and optical characterization of the oxide-based photonic structures. |
| 17:30 | UV-Assisted Atmospheric Pressure Spatial Atomic Layer Deposition of ZnO ABSTRACT. Ravi Raninga, Robert L. Z. Hoye, Judith Driscoll University of Cambridge, Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK ZnO has received much renewed interest as a wide band gap semiconductor for its variety of applications. For certain applications, such as thin film transistors, it is important to have highly crystalline ZnO with few defects, as a high defect concentration introduces too many charge carriers and can contribute to source-drain leakage. In this paper, we present a new roll-to-roll process, namely UV-Assisted Atmospheric Pressure Spatial Atomic Layer Deposition, for synthesizing high quality, crystalline ZnO. Using X-ray diffraction techniques, we show that the UV-activation of diethylzinc allows us to deposit c-axis oriented ZnO at temperatures as low as 50 °C with significantly improved crystallinity. This temperature is significant as it is below the glass transition temperature of polyethylene terephthalate (PET), a popular substrate in the field of flexible electronics. Our new process allows us to overcome the tendency of ZnO to be amorphous when grown below 100 °C. We also present the effect of growth under UV-illumination at different wavelengths on the defect states in ZnO with the use of X-ray photoemission spectroscopy, photothermal deflection spectroscopy and photoluminescence. |
| 17:30 | Ni-M (M=, Au, Pt, Pd) alloy formation during direct CH4 feeding over Ni-based anode type catalysts: EXAFS and XRD investigation ABSTRACT. L.F. Liotta1, A. Longo1,2, F. Puleo1, G. Pantaleo1, V. La Parola1, D. Banerjee3 1Istituto per lo Studio dei Materiali Nanostrutturati (ISMN)-CNR, UOS Palermo, Via Ugo La Malfa, 153, 90146 Palermo, Italy. Solid oxide fuel cells working at intermediate temperature (IT-SOFCs) represent a valid alternative technology for providing clean energy, due to their ability to directly oxidize methane obtained by industrial and municipal wastes or energy crops [1]. Renewable methane-based fuels, like biogas and natural gas, might be employed for the direct internal reforming of methane at the intermediate temperature range, i.e. ∼500–750 °C. Currently, the most common anode material for IT-SOFC is Ni-based cermet, namely nickel dispersed over the same material of the electrolyte, usually yttria-stabilized zirconia or ceria-gadolinia. However, nickel easily undergoes coke poisoning during oxidation of methane-containing fuels, with deleterious consequence on material durability and cell performance. As a consequence, today the main challenge for IT-SOFC technology consists in developing active anode materials able to directly oxidize CH4 and simultaneously to avoid carbon poisoning. A valid solution is to dope Ni with another transition metal, like Pt, Pd, Au, able to stabilize Ni as alloyed nanoparticles with improved resistance to coke poisoning [2,3]. The present work aims to investigate by EXAFS analysis the structural modification occurring over a Ni-based anode type catalyst doped by Pt, Au, Pd. XRD diffractograms were also recorded after flowing CH4 in the range of temperature between 500 and 750 °C. In figure the Fourier transformed EXAFS spectra of Ni-K edge, Au-LIII edge and Pt-LIII edge are displayed in three adjacent plots. The red curves correspond to the calcined NiAuPt catalyst, while the black plots are related to the same catalyst after flowing CH4 at 750 °C. [1] D.J.L. Brett, A. Atkinson, N.P. Brandon, S.J. Skinner, Chem. Soc. Rev. 37 (2008)1568–1578. [2] A. Horváth, L. Guczi, A. Kocsonya, G. Sáfrán, V. La Parola, L. F. Liotta, G. Pantaleo, A. M. Venezia, Appl. Catal. A 468, (2013) 250. [3] H. Wu, G. Pantaleo, V. La Parola, A. M. Venezia, X. Collard, C. Aprile, L. F. Liotta, Appl. Catal. B 156–157 (2014) 350. |
| 17:30 | Electrochemical Properties of Plasma Modified V2O5 in The Presence of Different Electrolytes ABSTRACT. Gamze Çelik Çoğal1, Esin Eren1, Abdulkerim Yıldız2 ,Songül Sen Gursoy3, Aysegul Uygun Oksuz1 1Department of Chemistry, Suleyman Demirel University, Faculty of Arts and Science, 32260 Isparta, Turkey gamzec3557@gmail.com, ayseguluygun@sdu.edu.tr Electrochromic materials can change their optical properties reversibly via an electrochemical reaction and are usually used in diverse fields of technology such as smart windows, light transmissive display devices etc [1]. Among inorganic metal oxide electrochromic materials, vanadium pentoxide (V2O5) is one of the most promising electrochromic materials because of its specific optical properties [2]. Moreover, V2O5 has both types of anodic and cathodic coloration characteristics. However, V2O5 films show both poor color contrast and slow switching time. To improve electrochromic properties, V2O5 can combine with other electrochromic materials such as conducting polymer [3]. In this study, low pressure rotating RF plasma reactor system was used to generate V2O5/Furan hybrid. V2O5 and V2O5 hybrid powders were coated on ITO-coated PET films using electron beam evaporation technique. The optical and electrochromic performance (such as switching time, coloration efficiency, etc.) of the flexible hybrids-based electrochromic films were investigated in presence of different electrolyte and compared with V2O5 films in detail. [1] Gozde Yurdabak Karaca, Esin Eren, Ceyda Alver, Umran Koc, Emre Uygun, Lutfi Oksuz, Aysegul Uygun Oksuz, Plasma Modified V2O5/PEDOT Hybrid Based Flexible Electrochromic Devices, Electroanalysis. [2] G. Ongeren, M. Sancak, M. Kiristi, A.Uygun Oksuz, L. Oksuz, J Inorg Organomet. Polym (2015) 25:1129–1136. Authors gratefully acknowledge the TÜBİTAK /COST (Project No: 114M877) for financial support to this study. |
| 17:30 | Ferroelectric photovoltaic effect in ferroelectric-semiconductor heterostructures ABSTRACT. J. P. B. Silva1,2, K. C. Sekhar2,3, F. Cortés-Juan4, R. F. Negrea5, A. C. Kuncser5, J. P. Connolly6, C. Ghica5, and J. Agostinho Moreira1, 1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal Ferroelectric materials are considered as promising candidates for photovoltaic applications because of their outstanding advantages over conventional p-n junction based photovoltaic devices, such as their high output voltage and polarization controlled PV response [1]. However in these materials, the short-circuit current density (Jsc) is lower than that in conventional solar cells due to inefficient radiation absorption and e-h generation [2]. For these reasons, PV devices based on ferroelectric materials have poor photovoltaic performance. Standard semiconductor based solar cells require a p-n junction, where the internal electric field near the junction interface is used for e-h pair charge separation. The main drawback of such structures however is that they cannot produce the open circuit voltage (Voc) greater than the semiconductor band gap, significantly limiting achievable efficiencies. The integration of semiconductor and ferroelectric materials takes the advantage of both the semiconductor and the ferroelectric properties and may lead to a high-efficiency photovoltaic effect [2]. In these ferroelectric-semiconductor heterostructures, e-h pairs are created inside both the semiconductor and ferroelectric layers. The depolarizing field and the interface charge coupling between the ferroelectric and semiconductor are crucial for the separation and transport of photo generated e-h through the heterostructures [2]. In this work, we investigate the PV response of Pt/0.5BZT-0.5BCT/ITO structures through the insertion of a semiconductor ZnO layer at different positions. The enhanced photovoltaic (PV) effect is observed when the ZnO layer is inserted between the Pt and the 0.5BZT-0.5BCT layers with the Voc≈-0.03 V and the Jsc ≈5.5 mA.cm-2. The photovoltaic effect is explained in terms of the alignment of the internal electric fields and by the polarization-dependent interfacial coupling effect at the ZnO/0.5BZT-0.5BCT interface, which was confirmed by investigating the role of polarization flipping on switchable photo response. [1] S. Sharma, M. Tomar, A. Kumar, N. K. Puri, V. Gupta, J. Appl. Phys. 118 (2015) 074103. [2] Z. Fan, K. Yao, J. Wang, Appl. Phys. Lett. 105 (2014) 162903. |
| 17:30 | Plasma modified WO3 Hybrids for High efficient flexible electrochromic devices ABSTRACT. Emre Uygun1, Esin Eren2, Ceyda Alver2, Gozde Yurdabak Karaca2, Lutfi Oksuz1, Aysegul Uygun Oksuz2 1Department of Physics, Suleyman Demirel University, Faculty of Arts and Science, 32260 Isparta, Turkey euygun@outlook.com, ayseguluygun@sdu.edu.tr Tungsten trioxide (WO3) is one of the most successful and frequently used inorganic electrochromic materials because of its robust behavior. However, some properties such as slow switching time restrict its application. Therefore, the hybrids prepared via hybridizing conducting polymer with WO3 have been considered to improve electrochromic performance via their complementary and synergistic effect [1,2]. The goal of this study is to prepare electrochromic hybrids based on WO3/PANI and its derivatives using rf rotating plasma modification method. The thin films of the hybrids were fabricated on flexible conducting polyethylene terephthalate films using electron beam evaporation and characterized using scanning electron microscopy (SEM). The solid-state electrochromic device (ECD) was constructed with a device structure consisting of PET/ITO|WO3 or WO3/PANI (its derivative)||gel electrolyte||ITO/PET. The electrochromic contrast, coloration efficiency and switching speed of ECDs were determined for electrochromic characteristics and compared to each other in detail. [1] C. Dulgerbaki, A. U. Oksuz, Fabricating polypyrrole/tungsten oxide hybrid based electrochromic devices using different ionic liquids, Polym. Adv. Technol. 27 (2016) 73–81. [2] M. Kiristi, F. Bozduman, A. U. Oksuz, L.Oksuz, A. Hala, Solid State Electrochromic Devices of Plasma Modified WO3 Hybrids, Ind. Eng. Chem. Res. 53 (2014) 15917−15922. Authors gratefully acknowledge the TÜBİTAK /COST (Project No: 114M877) for financial support to this study.
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| 17:30 | Fabrication and Electrical Characterizations of HfO2 Based Field Effect Transistors ABSTRACT. Ercan YILMAZ and Senol KAYA Abant Izzet Baysal University Center for Nuclear Radiation Research and Applications, Bolu 14280, Turkey Designing the advancement of fabrication of new high-k dielectrics system instead of the existing devices to improve devices performance has been extensively studied by researches since last few decades. Among the high-k materials, HfO2 are currently considered as the most suitable candidate to replace conversional SiO2 as the gate to solve scaling limit of SiO2 in MOS-based transistors. Hence in this study, we fabricate the p-channel MOSFETs with HfO2 gate dielectrics and the device characteristics including the structural and electrical specifications were investigated in details. It is seen that the HfO2 gate dielectrics were in cubic phase and surface roughness of the devices is approximately 2.8 nm which is convenient for MOS based devices. On the other hand, the electrical Id-V, transfer, and charge pumping characteristics does not show any anomalous kinks during the measurements and calculated interface state density and trapped charges in the oxide layers are order of 1011 cm-2. Considering to these results, we may conclude that, HfO2 MOSFET was successfully fabricated and may be used in novel technological applications. |
| 17:30 | Effect of Annealing on the Structural, Chemical and Electrical Characteristics of the HfO2 Thin Films ABSTRACT. Senol KAYA1, Ramazan LOK1, Aliekber AKTAG1, H. KARACALI1, Ilker YILDIZ2, Ercan YILMAZ1 1Abant Izzet Baysal University Center for Nuclear Radiation Research and Applications, Bolu 14280, Turkey Nowadays researchers have been considered to exploring the new high-k materials to be used in state of art CMOS technology to replace conversional SiO2 dielectrics. Various high-k dielectrics materials HfO2 have been considered, but the HfO2 has reported as one of the most promising materials among them. In addition, crystallization and morphological variations change the electrical performance of the device. Hence we aim to study effects of annealing temperature on the Structural, chemical and electrical characteristics of the HfO2 thin films deposited by RF sputtering. The annealing were performed at 300 °C and 550 °C in forming gas environment for 30 minutes. The structural characterizations were studied by XRD and AFM measurements while the chemical evolution and electrical characteristics were discussed by XPS and C-V measurements of the film, respectively. Results demonstrate that the film crystallinity were enhanced and surface roughness decrease with annealing. In addition, the SiO2 interfacial layer formation was observed after annealing and the peak intensity rise with annealing temperature. The capacitances of device significantly decrease after 550 °C annealing. It may be conclude that the optimum annealing temperature is 300 °C for the HfO2 to be used in MOS based technology. |
| 17:30 | Multi Process Thin Film Deposition and complex Sample Preparation Cycle under protected Atmosphere - a flexible Solution for highly Air, Humidity or Nitrogen sesitive Materials. ABSTRACT. Wolfgang Stein1, N.N.2 New materials or advanced functional films are always dedicated for specific aplications. Very often either the substrate material or the film material are strongly sensitive against normal environmetal conditions. Even if the components of such deposition are not sensitiv against such attac, the interfacing between substrate and film is effected from such influence. The solution in material research for such problems are isolated and strongly controlled conditions, which can be achieved with the use of glove boxes with integrated gas cleaning systems. The user interacts via isolation gloves to handle sensitive materials in the glove box wich are introduced to it via integrated load lock chambers. The combination of such controlled volume to any kind of deposition system is a problem, because normally no way exist to transfer such materials into separate deposition systems. Only a fully protected connection from such glove box to the deposition system allows an undisturbed transfer. But such way normally does not exist. SURFACE offers now fully integrated process systems which have a complete glovebox built in. In addition the complete design of such system recognizes the reduction of handling performance of the user caused by the thick gloves and its limited taktile sensitivities. Any services on such deposition system is generated from the atmospheriacl side, without disturbing the conditions of the contolled atmoshere in the glove box. The fully integrated style of the glove box reduces also the necessary floor space of such comlete set-up in the lab. As an example : the total foot print of a complet PLD Glove Box system including big Excimer laser, its gas cabinet, the process automation system with user interface, the vacuum chamber, cooling chiller and the gas control cabinet fits to a floor space of 3,5m x 0,8m and includes already the glove box workstation with a working width of 1 to 1,5 m. |
| 17:30 | Spin-lattice interactions in SmFeO3 ABSTRACT. Mads C. Weber1,2,3, Mael Guennou1, Michael C. Carpenter3, Donald McEvans3, Brahim Dkhil1,4, Jens Kreisel1,2 1Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg Multiferroic materials are of great current interest. These materials offer the possibility of manipulating the polarization state by a magnetic field or vice versa. In multiferroics, magnetism and electronic polarization can appear either independently or the polarization can be introduced by the magnetism [1]. For the latter case a good understanding of the spin-lattice coupling is crucial. In this context the family of rare-earth-ferrites (RFeO3) attract renewed attention thanks to a variety of different magnetic transitions. In the present work, we aim to shed light on the impact of magnetic transitions on crystal lattice of SmFeO3. SmFeO3 stands out of the rest of the rare-earth orthoferrites for its comparably high magnetic transition temperatures. To investigate the effect of the magnetic ordering on the crystal lattice we perform Raman spectroscopy (RS) and resonant ultrasound spectroscopy (RUS) while tuning the temperature through magnetic transitions with a particular focus on the spin-reorientation of the Fe3+-spin-sublattice (450-480 K) [2] and the low-temperature ordering of magnetic Sm3+ sublattice (~140 K) [3]. These two complementary techniques allow to obtain a macroscopic (RUS) and microscopic picture (RS) of the interaction between magnetism and lattice. During the Fe3+-spin reorientation phase, we find an important softening of the elastic constants in the resonant-ultrasound spectra whereas the Raman spectra do not show a significant anomaly. Towards lower temperatures the Sm3+ order; this ordering is clearly represented in the Raman spectra in the form of changes of the evolution of certain vibrational bands and additional bands appearing in the spectra. Since the vibrational displacements of the Raman bands are known [4], an analysis of the band anomalies with the Sm3+-spin ordering enables an in-depth understanding on the interaction mechanisms of the Sm3+-spin sublattice with crystal lattice. The effect of the Sm3+-spin ordering is only weakly represented in RUS underlining the importance to perform complementary measurement techniques to identify subtle impacts on the crystal structure such as spin-lattice coupling. [1] Khomskii, D. Classifying multiferroics: Mechanisms and effects. Physics (College. Park. Md). 2, 20 (2009). [2] White, R. L. Review of recent work on the magnetic and spectroscopic properties of the rare-earth orthoferrites, J. Appl. Phys. 40, 1061–1069 (1969). [3] Marshall, L. G. et al. Magnetic coupling between Sm3+ and the canted spin in an antiferromagnetic SmFeO3 single crystal, Phys. Rev. B 86, 64417 (2012). [4] Weber, M. C. et al. Raman spectroscopy of rare-earth orthoferrites RFeO3 (R =La, Sm, Eu, Gd, Tb, Dy), Phys. Rev. B 94, 214103 (2016). |
| 17:30 | Correlation of electronic structure and transport properties of iron perovskites at high temperature ABSTRACT. Artur Braun Empa, Swiss Federal Laboratories for Materials Science and Technology Überlandstrasse 129, CH – 8600 Dübendorf, Switzerland Rare earth-transition metal oxides (LnMeO3) are under scrutiny by solid state physicists for their transport properties such as metal-insulator transitions, super conductivity, and colossal magneto resistance. Conventional studies do not go significantly beyond ambient temperature. The need for superior electric conductivity at high temperatures ~ 500°C < T < 1000°C goes virtually unnoticed. There are indeed situations that require a high electrical or thermal conductivity at temperatures significantly higher than ambient temperature, such as solid oxide fuel cells, electrolysers and electronics in automotive under-the-hood applications. At such temperatures, conductivity is a thermally activated process and provided by electrons, polarons, oxygen ions, for instance. For example, the insulator LaFeO3 becomes semiconducting upon A-site substitution of La with Sr (hole doping) , and further conductivity increase is obtained by B-site substitution of Fe with Ni (band width control). I present results on the correlation of crystallographic and electronic structure and conductivity of a (111) single crystal of La1-xSrxFeO3-δ for 50°C < T < 500°C, including X-ray diffraction and core-level and valence band spectroscopy. Single crystal studies help us to better address the correlation of structure and transport properties in these energy relevant materials. [1] A. Braun, J. Richter, A. S. Harvey, et al. Electron hole–phonon interaction, correlation of structure, and conductivity in single crystal LSFO, Appl.Phys.Lett. 93, 262103, 2008. [2] A. Braun, D. Bayraktar, A.S. Harvey, et al. Pre-edges in oxygen (1s) x-ray absorption spectra: A spectral indicator for electron hole depletion and transport blocking in iron perov-skites, Appl.Phys.Lett. 2009, 94, 202102. [3] A Braun, X. Zhang, Y. Sun, et al. Correlation of high temperature X-ray photoemission valence band spectra and conductivity in strained LSFNO. Appl.Phys.Lett., 95, 022107, 2009. [4] A. Braun, B.S. Mun, Y. Sun, et al. Correlation of conductivity and angle integrated va-lence band photoemission characteristics in single crystal iron perovskites for 300K< T < 800 K. J. Electron Spectroscopy and Related Phenomena 181 (2010), 56-62. [5] S. Erat, A. Braun, C. Piamonteze, Z. Liu, et al.. Entanglement of charge transfer, hole doping, exchange inter-action and octahedron tilting angle and their influence on the conductivity of La1-xSrxFe0.75Ni0.25O3, J. Appl. Phys. 108, 124906 (2010). [6] A. Braun, S. Erat, A. Ariffin, et al. High temperature oxygen NEXAFS valence band spectra and conductivity of LaFe3/4Ni1/4O3., Appl.Phys.Lett. 99, 202112 (2011). [7] A. Braun, S. Erat, D. Bayraktar, et al. Electronic origin of conductivity changes and iso-thermal expansion of Ta- and Ti-substituted La1/2Sr1/2Fe-oxide in oxidative and reducing atmosphere, Chem. Mater. 2012, 24 (8), 1529–1535. [8] A. Braun. X-ray Studies on Electrochemical Systems - Synchrotron Methods for Energy Materials. 2017 Walter de Gruyter GmbH, Berlin/Boston. ISBN 978-3-11-043750-8. |
| 17:30 | Direct measurements of electrocaloric PbSc0.5Ta0.5O3 ceramics ABSTRACT. E. Stern-Taulats1,2, G. F. Nataf1, P. Lloveras3, M. Barrio3, B. Nair1, A. Planes2, J. Ll. Tamarit3, Ll. Mañosa2, N. D. Mathur1 and X. Moya1 1Department of Materials Science, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK The relaxor ferroelectric PbSc0.5Ta0.5O3 (PST) continues to be a promising electrocaloric material due to its room-temperature ferroelectric phase transition, high pyroelectric coefficient, and low hysteresis [1,2]. Direct electrocaloric measurements are challenging, and so the majority of electrocaloric studies on PST have been performed using indirect methods. We present direct measurements of isothermal heat Q and adiabatic temperature change ∆T using a bespoke calorimeter and an ultrafast infra-red camera. We find room-temperature values of Q ~ 850 J.kg-1 and ∆T ~ 1.8 K, for changes in electric field of 13.4 kV.cm-1. The values of Q and ∆T determined using these two independent techniques are in excellent agreement with each other, via values of specific heat measured at zero electric field. [1] L. Shebanov and K. Borman, Ferroelectrics 127, 143-148 (1992). [2] L. Shebanovs, A. Sternberg, W. N. Lawless and K. Borman, Ferroelectrics 184, 239-242 (1996). |
| 17:30 | Raman studies of domain walls in ferroelectrics and ferroelastics with Principal Component Analysis ABSTRACT. G. F. Nataf1,2,3, N. Barrett2, M. Guennou1, J. Kreisel1 1Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 Rue du Brill, L-4422 Belvaux, Luxembourg Ever since it has been realized that domain walls in ferroic materials can contain novel structural properties that does not exist in the bulk, researchers have considered a new paradigm of devices where the domain walls, rather than the domains, are the active element. This field has been coined “Domain Boundary engineering” [1,2] or “Domain wall nanoelectronics” [3]. One technique to get a better understanding of domain walls properties is Raman spectroscopy. The interpretation of Raman spectra near domain walls requires a good knowledge of the crystal symmetry and its optical properties but also new methods of analysis to overcome the spatial and spectral limit of resolutions of Raman spectroscopy. We present simulations showing that Principal Component Analysis (PCA) can be used to detect peak shifts, peak width and peak intensity variations in Raman spectra. We also study the example of 180°-domain walls in LiNbO3 and discuss the variations of the Raman modes at the ferroelastic domain walls of NdGaO3. [1] E. Salje and H. Zhang, “Domain boundary engineering,” Phase Transitions, vol. 82, no. 6, pp. 452–469, Jun. 2009. [2] E. K. H. Salje, “Multiferroic domain boundaries as active memory devices: trajectories towards domain boundary engineering.,” Chemphyschem, vol. 11, no. 5, pp. 940–50, Apr. 2010. [3] G. Catalan, J. Seidel, R. Ramesh, and J. F. Scott, “Domain wall nanoelectronics,” Rev. Mod. Phys., vol. 84, no. 1, pp. 119–156, Feb. 2012. |
| 17:30 | Facts and figures on the TO-BE COST action ABSTRACT. This poster will give an overview of the activities carried out within the TO-BE COST action and relevant statistics. |