Structural and Dielectric Properties of La0.33Sr0.67M0.33Ti0.67O3±δ (M = Mn or Fe) Perovskites

We have investigated the structural and dielectric properties of La0.33Sr0.67Mn0.33Ti0.67O3+δ (LSMTO) and La0.33Sr0.67Fe0.33Ti0.67O3−δ (LSFTO) perovskites synthesized by the solid-state reaction method at 1500 ∘C Rietveld analysis of X-ray diffraction (XRD) data shows pure crystalline phase with cubic Pm3̄m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$Pm\bar {3}m$\end{document} structure, with no change in the unit cell volume due to the same ionic radii of Fe3+ and Mn3+. Scanning electron microscopy (SEM) micrographs show that the average grain size is slightly larger for LSMTO than for LSFTO. The electrical response of samples was studied at room temperature using the impedance spectroscopy technique over a broad frequency range (0.1Hz1MHz). The conductivity curves for the two samples were well fitted by the Jonscher law. For the LSFTO sample the hopping process occurs at long distance whereas for LSMTO compound, it occurs between neighboring sites. Variation of the dielectric parameter (ε′) and that of the loss factor (ε″) for both samples were explained by the different polarization and conductivity mechanisms. For both compounds, the variation of the imaginary part Z? shows a peak at a relaxation frequency (fr) related to the relaxation time (τ) by τ = 1/2πfr. Cole-Cole plots of impedance show the presence of two semicircles for LSMTO sample, whereas LSFTO compound shows one semicircle. To explain the impedance results, an appropriate electrical equivalent circuit has been proposed for each sample.