Physico-Chemical nanomaterials science
Anomalous dielectric relaxation in Na0.5Bi0.5TiO3
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

The specific dielectric response of the ferroelectric relaxors is determined by the presence of nanometer scaled polar regions at that macroscopically the symmetry of the crystal structure remains nonpolar. Lead free ferroelectric relaxor Na0.5Bi0.5TiO3 (NBT) is considered as promising material for microelectromechanical systems, pyroelectric sensors, multilayer capacitors, and others [1]. In this work we report the results of studying electrical properties of previously untreated as well as heat treated in air and in vacuum NBT single crystals. The samples prepared from as-grown crystals, were annealed in air at 1070 K for 1 h and then in vacuum at 1070 K for 2 h. Electrical properties were measured in AC field (0.5-100 kHz), the temperature of the samples was changed in the interval 300-800 K. The measurements were performed after each heat treatment step.
Strong anomaly of permittivity dependence ε(T) was found near 670 K. It was shown that frequency dispersion of ε anomaly did not correspond to simple Debye spectral function. Nearly symmetrical ε(T) peak was observed instead of step-like temperature anomaly predicted by Debye model. Increase of measuring field frequency led to sharp decrease of ε(T) peak magnitude. To explain the experimental data, the thermal decay of the dipole centers contributing to permittivity, was considered. The specific dispersion of ε was observed if the characteristic time of the dipole defects decay became comparable with the time of temperature cycling in the experiment. Analysis of the data obtained for un-treated and heat-treated samples [2] made it possible to propose that the dipole defects responsible for permittivity relaxation were formed by Ti ions captured an electron and located nearby oxygen vacancy VO. 

1.	Priya S., Nahm S. (2012) Lead-Free Piezoelectrics. Springer, New York.
2.	Sidak V.M., Trubitsyn M.P. Dielectric relaxation and the dipole defects in Na0.5Bi0.5TiO3 single crystal // Appl Nanosci. - 2021. https://doi.org/10.1007/s13204-021-01712-y