Dielectric relaxation induced by oxygen vacancies in Na$_{0.5}$Bi$_{0.5}$TiO$_{3}$ ceramics

TL;DR

This study investigates how oxygen vacancies influence dielectric relaxation in Na$_{0.5}$Bi$_{0.5}$TiO$_{3}$ ceramics, revealing that vacuum heat treatment enhances dielectric permittivity and induces non-stable polarization effects.

Contribution

It demonstrates that oxygen vacancies and localized electrons significantly affect dielectric anomalies, introducing a thermally stimulated decay model for polarization in relaxor ferroelectric ceramics.

Findings

Vacuum heat treatment increases dielectric permittivity to ~10^4.

Dielectric anomalies are linked to space charge polarization mechanisms.

Non-stable polarization vanishes upon heating in air up to 800 K.

Abstract

Dielectric permittivity was studied in ceramics of relaxor ferroelectric bismuth-sodium titanate Na$_{0.5}$Bi$_{0.5}$TiO$_{3}$. The measurements were performed on as sintered and heat treated in vacuum samples. The diffuse dielectric anomalies associated with the structural phase transitions were observed in as sintered samples. The intense peak of permittivity ($ \varepsilon_{\text{max}} \sim 10^{4}$) appeared after heat treating in vacuum. The anomaly of $\varepsilon(T)$ was contributed by slow polarization processes ($f<10$ kHz) and was non-stable, vanishing on heating in air up to $\sim 800$ K. Temperature and frequency dependencies of $\varepsilon$ were described by using Cole-Cole model with accounting thermally stimulated decay of the non-stable polarization. It is supposed that the dielectric anomaly is determined by space charge polarization mechanism. Oxygen vacancies V$_{\rm{O}}^{\bullet \bullet}$ and electrons localized on titanium ions Ti$'_{\rm{Ti}}$ are assumed to be responsible for the phenomenon observed.