Low temperature conductivity of BaFe$_{0.5}$Nb$_{0.5}$O$_3$ double perovskite structure ceramics

TL;DR

This study investigates the low-temperature electrical conductivity mechanisms in BaFe$_{0.5}$Nb$_{0.5}$O$_3$ ceramics, revealing the roles of electronic and ionic conduction, defect states, and phonon contributions through detailed experimental analysis.

Contribution

It provides a comprehensive analysis of charge transport mechanisms in BFN ceramics, including defect-related conduction, polaron tunneling, and variable range hopping models, at low temperatures.

Findings

Electronic conductivity obeys Jonscher's power law.

Conductivity follows Mott VRH model with decreasing temperature.

Activation energies for electrons and ions are 317 meV and 17 meV, respectively.

Abstract

In this work, we explore the origin and type of charge carriers, and their transport mechanism in polycrystalline barium-iron-niobate (BFN, BaFe$_{0.5}$Nb$_{0.5}$O$_3$) ceramics, at lower temperatures between 20K and 300K. The observed point defects at grain andsurface defects at grain boundary region are responsible for the electronic conductivity, whereas dipoles at grain boundary region are responsible for the ionic conductivity, these independent electronic and ionic conductivity were responsible for the total conductivity of our BFN sample. The required activation energy for conduction of electrons in grain boundary region and ions in grain region were calculated to be 317 meV and 17 meV respectively. The electronic conductivity of grain region obey Jonscher's power law. Analysis of the temperature dependent frequency exponent suggest that the electronic conductivity of grain follows the overlapping large polaron tunneling (OLP) model. The temperature dependent conductivity follows the Mott variable range hopping model(VRH), showing hopping range increases with decreasing temeprature. The defect density of the grain obtained to be $3.17 \times 10^{17}$ eV/cm$^3$. The contribution of phonon to the conductivity understood by considering Schankenberg model, activation energy of 110 meV corresponds to the multiphonon (both optical and acoustic) and 1.6 meV corresponds to acoustic phonon only. Our systematic study provides in-depth understanding of the low temperature conductivity mechanism of polycrystalline BFN ceramics.