Nonstoichiometry and physical properties of the perovskite Ba_xLa_1−xFeO_3−y system

Abstract

A series of samples in the Ba_xLa_1−xFeO_3−ysystem (x=0.00, 0.25, 0.50, 0.75, and 1.00) have been prepared at 1200°C under an atmospheric air pressure. The solid solutions of the system were analysed from the X-ray diffraction spectra and thermal analyses. X-ray diffraction studies assigned the compositions of the x=0.00 and 1.00 to the orthorhombic system and the compositions of the x=0.25, 0.50, and 0.75 to the cubic system. The reduced lattice volume increased with the x value in the system. The mole ratios of the Fe⁴⁺ ion in the solid solutions, or τ values, were determined by Mohr salt analyses and the non-stoichiometric chemical formulae of the system were formulated from the x, τ, and y values. From the results of the Mössbauer spectroscopy, the coordination and the magnetic property of the iron ion have been discussed. The electrical conductivities were measured as a function of temperature under atmospheric air pressure. The activation energy was minimum at the composition of x=0.50. The conduction mechanism can be explained by the hopping model between the mixed valences of the Fe³⁺ and Fe⁴⁺ ions.