Physico-Chemical nanomaterials science
Space-charge polarization phenomena                           in single crystal and ceramics of bismuth sodium titanate 
V.M. Sidak1, M.P. Trubitsyn2
1 Biomedical Physics and Informatics Department, Dnipro State Medical University, Vernadsky str. 9, Dnipro-49044, Ukraine
E-mail: vasylsidak@gmail.com
2 Department of Experimental Physics, Oles Honchar Dnipro National University, Gagarina ave. 72, Dnipro-49010, Ukraine

Bismuth sodium titanate Na0.5Bi0.5TiO3 (NBT) is a lead-free relaxor ferroelectric which electrical properties in broad temperature and frequency ranges are determined by polar nanometer sized clusters [1]. NBT is considered as promising material for use in functional electronics due to high dielectric permittivity, piezoelectric and pyroelectric coefficients. Previously, slow dielectric relaxation with a specific frequency dispersion was observed in NBT crystals around 670 K [2]. Dielectric anomaly disappeared after the heat treatment in air (870 K) and could be restored by the subsequent treatment in vacuum (1070 K). To explain the unusual ε(T, ω) dependences, the thermal decay of the dipole centers was taken into account. The data obtained showed that the relaxation of ε was determined by the defects based on oxygen vacancies (VO). The observed non-equilibrium polarization processes earlier were related to dipole centers formed by Ti ions that captured electrons and located near VO. However, the typical values of permittivity in maximum (~104) are too high for dipole defects contribution and more likely evidence for space-charge polarization phenomena. Similar giant permittivity is actively studied and discussed for another compounds of perovskite family [3]. To obtain the information on the mechanisms of the assumed space-charge polarization, we study and compare the data on slow dielectric relaxation in NBT single crystal and ceramics.

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2.	Sidak, V.M., Trubitsyn, M.P. Dielectric relaxation and the dipole defects in Na0.5Bi0.5TiO3 single crystal // Appl Nanosci. - 2022. -12. –P. 775-780.
3.	Laxman Singh, Rai U.S., Mandal K.D., Singh N.B. Progress in the growth of CaCu3Ti4O12 and related functional dielectric perovskites // Prog. Cryst. Growth Charact. Mater. -2014. http://dx.doi.org/10.1016/j.pcrysgrow.2014.04.001