Nonstoichiometry and Physical Properties of the Perovskite CaGa1-xFexO3-y System

摘要

A series of solid solutions of the CaGa1-xFexO3-y system with the compositions of x=0.25, 0.50, 0.75, and 1.00 has been prepared at 1150?é under an atmospheric air pressure. The structure, nonstoichiometric chemical formula, and the distribution of cations for the solid solutions are determined by X-ray diffraction analysis, Mohr salt titration, Mossbauer spectroscopic analysis. Their physical properties are discussed with electrical conductivity and magnetic measurements. The crystal system of all the compositions is a brownmillerite orthorhombic system from the X-ray diffraction analysis and the reduced lattice volume increases linearly with x value except that of the composition of x=0.25. All the solid solutions do not contain Fe4+ ion and the mole number of oxygen vacancies or y value is 0.50 from Mohr salt analysis. The oxidation state of Fe ion, the coordination state, the structure change in the Brownmillerite-type structure, and the distribution of Ga3+ and Fe3+ ions are discussed with Mossbauer spectroscopic analysis. The electrical conductivity increases and activation energy decreases, as x value increases. The traditional semiconducting property of this system is described in terms of band theory. The compositions of x=0.50?-1.00 show a thermal magnetic hysteresis in the magnetic measurement with the cooling conditions, which is discussed in terms of the space group and Dzyaloshinsky-Moriya interaction.