Structural, optical and electrical conductivity analysis of iron supplanted LaPrCoMnO6 system for electrochemical applications

Abstract

Double perovskite system LaPrCo_1 − xFe_xMnO₆; (x = 0.2, 0.5, 0.8 and 1.0) was developed by sol-gel method and its structural, microstructural, optical as well as electrical properties were investigated. X-Ray Diffraction analysis inveterate the phase formation with monoclinic structure (P2₁/n) as well as a slight shifting of diffraction peaks towards left is noticed with substitution of Fe³⁺ for Co²⁺. The crystallite size as well as strain, both exhibited similar tendency with x and varies from 506 Å to 1100 Å and 0.94 × 10^− 3 to 1.87 × 10^− 3, respectively and both the parameters showed their maximum value for x = 0.5 composition. Field Emission Scanning Electron Microscopy study divulged that mean grain size is of micrometre order (1.27 to 1.96 μm, maximum for x = 0.5) and EDX analysis confirmed the availability of all anticipated elements. High Resolution Transmission Electron Microscopy with Selected Area Electron Diffraction (SAED) pattern confirmed the crystallinity as well as purity of prepared system with inter-planar spacing 0.286 nm for x = 0.2 composition. X-Ray Photoelectron Spectroscopy analysis inveterate coexistence of various oxidation states of transition metal cations such as + 2/+3 for cobalt and iron whereas + 3/+4 for manganese. Ultra Violet-Visible-Near Infrared (UV-Vis-NIR) reflectance spectra inveterate semiconductor type band gap of ~ 2 eV with a maximum optical band gap of 2.13 eV for x = 0.5 composition. DC conductivity analysis suggested semiconducting behaviour and followed both thermal activation and variable range hopping conduction mechanisms. Three different slopes in Arrhenius plot with distinct activation energies inveterate the presence of electronic as well as ionic conduction. DC conductivity decreased initially with Fe substitution, afterwards displayed increasing behaviour up to x = 0.8, and then again decreased for x = 1.0. The decrease in DC conductivity suggested weakening of double-exchange interactions due to decrease in ratio of Mn³⁺/Mn⁴⁺ (and Co²⁺/Co³⁺) on substitution of Fe³⁺ for Co²⁺. The synthesized LaPrCo_1 − xFe_xMnO₆ system displayed good electronic/ionic conductivity, making it apposite for electrochemical devices.