High temperature dielectric and impedance spectroscopy study of LaCo$_{0.7}$Nb$_{0.3}$O$_3$

TL;DR

This study investigates the high-temperature dielectric and impedance properties of Nb-doped LaCoO$_3$, revealing temperature-dependent dielectric constant, conduction mechanisms, and grain boundary effects, highlighting its semiconducting behavior.

Contribution

It provides a detailed analysis of the dielectric and impedance behavior of LaCo$_{0.7}$Nb$_{0.3}$O$_3$ at high temperatures, including charge carrier activation and grain boundary contributions.

Findings

Maximum dielectric constant of ~1400 at 400 K

Activation energy increases from 0.44 eV to 0.56 eV around 400 K

Conductivity increases with temperature and frequency, indicating semiconducting behavior

Abstract

We report the high temperature dielectric and {\it ac} impedance spectroscopy investigation of Nb substituted LaCo$_{0.7}$Nb$_{0.3}$O$_3$ polycrystalline sample. The maximum dielectric constant value was observed $\approx$1400 at around 400~K where the peak value shows a decreasing trend at higher temperatures and frequency. Similar variation was reflected in the dielectric loss (tan$\delta$) behavior with temperature, which shows the thermal activation of the charge carriers in the material. The analysis of high temperature impedance spectroscopy data shows the grain and grain boundary contributions by fitting the Nyquist plots to the equivalent circuit. From the analysis of the impedance and modulus spectra, it was possible to discern between the effects of overlapping grains, grain boundaries, and electrode interfaces. The relaxation time decreases with an increase in the temperature and the activation energy changes from 0.44~eV to 0.56~eV at around 400~K, which is due to involvement of thermal activation in the conduction of charge carriers. The conductivity is found to be increased with temperature for a given frequency, which again shows the semiconducting behavior. Whereas the conductivity increases with increase in frequency at lower temperatures. Also, the conductivity almost saturates with frequency at high temperatures.