Abstract: Investigations of flexoelectric effect is a hot topic. Since the flexoeffect is defined by gradients of polarization and elastic strains, which obligatory exist in nanos, where all the properties change strongly from the surface to the bulk, we introduced the spontaneous flexoeffect [1], and establish its key role for explanation of mysterious experimental results. The strong influence of spontaneous flexoeffect explains unexpected phenomenon in nanos – the critical size disappearance at size-induced phase transition and reentrant ferroelectric phase appearance. This phenomenon was observed in BaTiO₃ nanospheres of radii 5–50 nm and was a puzzle up to our paper [2], where we explained it by the spontaneous flexoeffect and Vegard strains, created by oxygen vacancies. The developed mechanism opens the ways for miniaturization of electronic devices up to a few nm sizes. More than 15 years ago the appearance of ferroelectricity was observed in bulk PZN-PLZT relaxor sintered in nitrogen atmosphere, which induce high concentration of oxygen vacancies. This phenomenon stayed unexplained, until we have shown [3] that the transition from relaxor to ferroelectric state is possible at high concentration of the vacancies, which are elastic dipoles, due to electrostriction, flexoelectric and Vegard effects. The flexoelectric origin of morphotropic region with high electromechanical properties in relaxors is very important for high-sensitive ultrasound devices. Recently we study the polar phenomenon in low-dimensional transition metals dichalcogenides, and have shown that spontaneous out-of-plane polarization arises from the flexoeffect due to spontaneous bending and inversion symmetry breaking in the vicinity of surface/substrate. [4].

Keywords: Spontaneous Flexoelectric Effect, Nanomaterials, Vacancies, Ferroelectricity.

1. E.A.Eliseev et al, Phys. Rev. B 79, 165433(10) (2009).
2. A. N. Morozovska, M. D. Glinchuk, J. Appl. Phys. 119, 094109(8) (2016).
3. M. D. Glinchuk et al, Phys.Rev. B 98, 094102 (2018).
4. A. N. Morozovska et al., Phys. Rev. B 102, 075417 (2020).

Biography: Prof. Maya Glinchuk graduated from Kiev State University with Honour Degree, received her PhD in Physics and Mathematics from Moscow State Pedagogical Institute and her Doctor of Science in Physics and Mathematics from Institute of Physics of Semiconductors National Academy of Sciences of Ukraine, Kiev. She is Full Professor in Physics and Mathematics and Corresponding Member of National Academy of Science of Ukraine. In 90’s years Maya Glinchuk became a member of several International Committees, namely International Advisory Committee on Ferroelectricity, European Advisory Committee on Ferroelectricity, AMPERE Committee. Many years she is member of Editorial Board of international journal Ferroelectrics. Maya Glinchuk is author of 370 scientific papers and several books in solid state physics with h-index 32 according to Scopus.