Magnetic, Optical, Electrical and Charge Storage Capacity of Ca2+ and Sr2+ Doped Lanthanum Ferrite Ceramics

Abstract

Perovskite ABO3 type lanthanum ferrite (LaFeO3) is attractive due to their multifunctionality and application as a dielectric material, multi-ferroic material, catalyst and sensing material. This ortho-ferrite also possesses week magnetic and conducting properties. Doping either at the ‘A’ site or ‘B’ site of the perovskites change the average valance of the ‘B’ site cation and generates plenty of oxygen vacancies in the crystal lattice. Defect engineering is a useful strategy to enhance the performance of the perovskite materials. In this present work lanthanum ferrite, 40 mole% Ca2+ doped LaFeO3 (LCF) and 40 mole% Sr2+ doped LaFeO3 (LSF)are synthesized by sol-gel auto-combustion process with additional high temperature calcination process. The prepared samples are characterized with X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy-energy dispersive X-ray analysis (FESEM-EDX). XRD reveals the formation of single phase material without any peaks of dopant phase. Raman spectroscopy displays an interesting feature that all the Raman modes of LaFeO3 are fading out in LCF and vanished completely in LSF. FESEM-EDX analysis shows agglomerated grains with visible grain boundaries while elemental weight% is maintained. Diffuse reflectance spectroscopy (DRS) shows that upon doping Ca2+and Sr2+ the absorption edge shifted from visible to ultra violet region. Vibrating sample magnetometer (VSM) study exhibits significant improvement of coerceivity with slight downfall of magnetisation in doped LaFeO3 than the pristine one. DC four probe conductivity analysis from room temperature to 950°C revealssuperior conductivity of LSF (~250 S/Cm) and LCF (~120 S/Cm) than LaFeO3 itself. Charge storage behaviour is measured by the specific capacitance measurement from cyclic voltammetry analysis in a conventional three electrode setup using 1(M) KOH as an electrolyte. Specific capacitance is also improved for doped materials and this enhancement can be explained on the basis of enhanced conductivity of doped LaFeO3 than the pristine LaFeO3.