Enhancement in magnetic and dielectric properties of La and Pr co substituted BiFeO3

This report underlines the systematic studies of crystalline structure, magnetic and ferroelectric properties of polycrystalline Bi-1 (x) yLaxPryFeO3 ceramic samples, in which x changes continuously from 0 to 0.2 for y = 0 and y from 0 to 0.2 for x = 0.2. X-ray diffraction (XRD) patterns revealed that La and Pr substitution at Bi site in the ceramic eliminates the usual impurity phases completely. Rietveld refinement of the XRD patterns shows that the crystal structure changes gradually from Rhombohedral (R3c) to Orthorhombic (pbnm) with increasing La and Pr concentration. This transition has significant effects on the multiferroic properties of Bi-1 (x) yLaxPryFeO3 ceramics. Substantial enhancement in magnetization of Bi-1 (x) yLaxPryFeO3 has been observed and this is found to be correlated with the evolution of structural phase change with doping of Pr in samples having lanthanum concentration of x = 0.2. This leads to the suppression of helical spin order. However, the enhancement in magnetic behavior also takes place due to nanocrystallite nature of Bi-1 (x) yLaxPryFeO3 (x = 0.2, y = 0.05-0.2). For the nanocrystallites having sizes lower than 62 nm, which is the period of spin cycloid, this spin configuration will get destroyed resulting in the enhancement of magnetization. The studies of microstructures employing SEM and TEM revealed that Bi-1 (x) yLaxPryFeO3 consists of nano size grained microstructures. It is also found that dielectric constant and dielectric loss get improved by La and Pr co-substitution. The dielectric constant for x = 0.0, y = 0.0 is 81 which changes to 354 for x = 0.2, y = 0.15 at 100 Hz. Dielectric losses are strongly diminished from 0.960 for x = 0.0, y = 0.0, 0.321 for x = 0.2, y = 0.0 and to 0.20 for x = 0.2, y = 0.05 at 100 Hz. This improvement in dielectric properties is likely due to the changes of lattice parameters and suppression of oxygen vacancies caused by La and Pr co substitution. (C) 2012 Elsevier B.V. All rights reserved.