Unravelling the effect of Cr doping on electronic transport properties of barium calcium titanate ceramics

The present paper investigates effect of Cr doping on AC conductivity, electric modulus and impedance spectroscopy on Barium Calcium Titanate ceramics synthesized by standard solid state reaction method in the frequency range 100 Hz-1 MHz from 633 to 773 K. With increase in Cr content frequency dependent AC conductivity show mixed behavior and found to obey Almond-West Law. Various parameters viz. sigma dc, omega H and s have been extracted from the fitting of sigma 'omega\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\sigma }{\prime}\left(\omega \right)$$\end{document} with Almond West Law. Conduction mechanism in studied ceramics has been determined by analyzing frequency exponent and found that conduction occurs via Overlapping Large-Polaron Tunnelling. The activation energy for DC conduction lies between 0.72 and 0.53 eV. Relaxation time and activation energy for dielectric relaxation determined from fitting of imaginary part of electric modulus is in the range of 3.47 mu s to 190.56 mu s and 0.99 to 0.74 eV respectively. Nyquist plots consist of two combined semicircles, signifying the simultaneous involvement of both grain and grain boundaries in the high and low-frequency regions and are fitted with a series combination of two R-CPE equivalent circuits indicating non-Debye type relaxation. Both grain and grain boundaries resistances estimated from fitting of Nyquist's plots using equivalent circuits are found to decrease with temperature indicating the semiconducting nature of the studied ceramic samples.