Estimation of relaxor behavior in Sr2+ doped Na0.5Bi0.5TiO3 ceramics

Abstract

An attempt has been made to study the relaxation mechanism of nanoscopic polar regions (PNRs) in Sr2+ doped Na0.5Bi0.5TiO3 relaxors; in particular, the compositions (0.90Na0.5Bi0.5TiO3–0.10SrTiO3, 0.80Na0.5Bi0.5TiO3–0.20SrTiO3, 0.70Na0.5Bi0.5TiO3–0.30SrTiO3) with temperature stable dielectric permittivity > 4500 over a broad range of working temperatures are chosen for this work. The temperature and frequency dependent growth and dynamics of these PNRs are investigated around the three crucial temperatures-$$T_{\text{B}}$$ (Burn’s Temperature), $$T_{\text{m}}$$ (temperature of maximum dielectric permittivity) and $$T_{\text{f}}$$ (freezing temperature) employing some empirical models and IS technique. Careful examination of combined plots of normalized $$M^{\prime\prime}\left( f \right)$$ and $$Z^{\prime\prime}\left( f \right)$$ spectra suggest a transition from long range ordering to short range dipolar relaxation as samples are cooled from above $$T_{\text{B}}$$ to below $$T_{\text{f}}$$. Activation energies derived from the Arrhenius fit of $$f_{\hbox{max} }$$ (from $$M^{\prime\prime}\left( f \right)$$ plot) reveal different relaxation mechanisms of the PNRs in three separate temperature domains around $$T_{\text{B}}$$, $$T_{\text{m}}$$ and $$T_{\text{f}}$$. This is also advocated by the analysis of stretched exponent $$\beta$$ obtained from Gaussian and KWW fit. Further, a scaling study made on the $$M^{\prime\prime}\left( f \right)$$ spectra predicts temperature sensitive dipolar relaxation. The present study may add a new dimension to the establishment of NBT-ST relaxor ceramics as potential material for capacitor applications at a higher temperature.