Influence of co-substitution driven property tailoring in lanthanum orthoferrites (LaFeO3)

Abstract

Abstract In this paper, effect of partial co-substitution (La by Li at A-site and Fe by Mn at B-site) on structural, electrical, optical and magnetic properties of perovskite type LaFeO 3 is reported. Polycrystalline La 1−x Li x Fe 1−y Mn y O 3 (x = y = 0–0.2) has been prepared by modified Pechini route. X-ray diffraction (XRD) results confirmed single phase polycrystalline powder. Effect of co-substitution on structural property has been noted in terms of changes in Fe/Mn-O-Fe/Mn bond angle and lattice strain on Rietveld refinement. The co-substitution driven structural changes have also been corroborated by fourier transform infrared (FTIR) spectrum in terms of upward shift of Fe/Mn-O stretching mode and downward shift of Fe/Mn-O-Fe/Mn bending mode of vibrations. Surface morphology of the materials indicated typical nanocrystalline microstructure with visible change in grain size with change in substituent concentration. Structural changes on co-substitution has significant effect on magnetic property tailoring arising due to deviation in Fe/Mn-O-Fe/Mn bond angle and/or indirect exchange interactions between two magnetic sub lattices Fe/Mn via intervening oxygen ion. The dielectric spectrum exhibited typical non-Debye type response as confirmed by modulus spectrum which shows peak at specific frequency for all concentration accompanied by shift of peak position towards higher frequency side with increasing concentration. Estimated relaxation time and electrical conductivity shows thermally activated Arrhenius type response with a maximum conductivity ~ 5.37 × 10 −4 S cm −1 at 423 K for 20% co-substitution. This is attributed to combined effect of grain and grain boundary contribution.