Suchergebnisse

This work has been supported by the National Research Program in the framework of the project "Multifunctional Materials and composites, photonics and nanotechnology (IMIS2)." ; Direct and indirect studies of the electrocaloric effect were carried out in poled and depoled Na0.5Bi0.5TiO3. For this purpose, polarization and electrocaloric effect temperature change measurements were made at different electric field pulses as a function of temperature. The applicability of the widely used indirect electrocaloric effect determination method, using the Maxwell relation, was critically analyzed with respect to the reliable direct measurements. Quantitative differences were observed between the results obtained by both approaches in the case of the poled Na0.5Bi0.5TiO3 sample. These differences can be explained by the temperature-dependent concentration of domains oriented in the direction of the applied electric field. Whereas in depoled Na0.5Bi0.5TiO3, which is characterized by the electric field dependence of polar nanoregions embedded in a nonpolar matrix, the Maxwell relation is not applicable at all, as it is indicated by the obtained results. Possible mechanisms which could be responsible for the electrocaloric effect in the relaxor state were considered. The results of this study are used to evaluate the numerous results obtained and published by other authors, using the Maxwell relation to indirectly determine the electrocaloric effect. The reason for the negative values of the electrocaloric effect, obtained in such a way and widely discussed in the literature in the case of Na0.5Bi0.5TiO3, has been explained in this study. ; National Research Program (IMIS2); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The intrinsic mobile interfaces in ferroelectrics—the domain walls can drive and enhance diverse ferroelectric properties, essential for modern applications. Control over the motion of domain walls is of high practical importance. Here we analyse theoretically and show experimentally epitaxial ferroelectric films, where mobile domain walls coexist and interact with immobile growth-induced interfaces—columnar boundaries. Whereas these boundaries do not disturb the long-range crystal order, they affect the behaviour of domain walls in a peculiar selective manner. The columnar boundaries substantially modify the behaviour of non-ferroelastic domains walls, but have negligible impact on the ferroelastic ones. The results suggest that introduction of immobile boundaries into ferroelectric films is a viable method to modify domain structures and dynamic responses at nano-scale that may serve to functionalization of a broader range of ferroelectric films where columnar boundaries naturally appear as a result of the 3D growth. ; The authors are grateful to Prof. A. Gruverman for useful discussions. Marijke Spanjer is acknowledged for proofreading the manuscript. PY acknowledges the Russian Foundation for Basic Research, Grant No. 19-02-00938. The study of the interaction of ferroelastic DWs with CBs was carried out under a state contract with IT SB RAS. KS acknowledges the support by the French Government "Investments for the Future" Program, University of Bordeaux Initiative of Excellence (IDEX Bordeaux), and by the Generalitat de Catalunya (Grant No. 2017SGR 1506). PY, AD and MT acknowledge the Operational Program Research, Development and Education, financed by the European Structural and Investment Funds and the Czech Ministry of Education, Youth, and Sports (Project No. SOLID21, CZ.02.1.01/0.0/0.0/16_019/0000760). MT acknowledges support from the Czech Science Foundation (Grant No. 19-09671S). JP acknowledges the funding from the Academy of Finland (Grant No. 298409). ; Peer reviewed