The surface piezoresponce and electric potential of the c-oriented Sr0.5Ba0.5Nb2O6/Pt/Al2O3 thin films

This work was supported by the Ministry of Education and Science of the Russian Federation (research projects No. 3.1649.2017/4.6 and No. 3.6439.2017)

Twin-boundary engineering and thickness effect on strontium-barium niobate thin films on MgO substrate

International audienceThe Sr0.5Ba0.5Nb2O6 (SBN50) films with different thicknesses synthesized by a high-current discharge rfsputtering in an oxygen atmosphere. All synthesized films have the structure of tetragonal tungsten bronze. The dependence of the unit cell parameters of the film material demonstrates a size effect, the magnitude of which is comparable to the distortions resulting from the ferroelectric relaxor phase transformation of SBN crystals of the same composition. The twinning of the same type is observed in all films when the twinned film components are rotated relative to each other by 36.8 degrees around the fourth-order rotational axis. The orientation of the films relative to the substrate can be written as [001]SBN parallel to[001]MgO; [100] SBN+parallel to[310]MgO and [100]SBN-parallel to[3 (1) over bar0]MgO, where the sign ``+'' and ``-'' marks the twin components. It is noteworthy that such an orientation of the film relative to the substrate corresponds to the maximum possible tensile stress of heteroepitaxial films acting from the MgO single crystal substrate. This type of twinning is not typical for SBN50 films on MgO grown by other synthesis methods. The appearance of this unusual type of twinning is associated with the peculiarities of synthesis. At the initial moment of sputtering, the substrate is additionally heated by the sputtered substance's plasma. The substrate temperature can also be used in other synthesis methods to control twinning and strain in barium strontium niobate thin films. (C) 2021 Elsevier B.V. All rights reserved

Direct transition from the rhombohedral ferroelectric to the paraelectric phase in a (Ba,Sr)TiO

A heteroepitaxial (200 nm thick) $\text{Ba}_{0.8}\text{Sr}_{0.2}\text{TiO}_{3}$ (BST) thin film was deposited on a (111)MgO substrate using rf sputtering. X-ray diffraction examinations confirmed epitaxial growth and rhombohedral symmetry of the film ($a = 0.39616(2)\ \text{nm}$ and $\alpha = 89.52(3)^\circ$ ) at room temperature. Polarized Raman spectra of the film were studied in the temperature range from 100 to 420 K. In contrast to a BST thin film grown on (001)MgO, the observed linear temperature dependence of the squared soft mode frequency suggests the displacive character of the ferroelectric-paraelectric phase transition in a BST thin film on (111)MgO