Structure and magnetism of Pr1-xSrxFeO3-δ

Crystal structure, redox, and magnetic properties for the Pr1-xSrxFeO3-delta solid-solution phase have been studied. Oxidized samples (prepared in air at 900 degrees C) crystallize in the GdFeO3-type structure for 0 less than or equal to x less than or equal to 0.80, and probably in the Sr8Fe8O23-type (unpublished) structure for x = 0.90. Reduced samples (containing virtually only Fe3+) crystallize as the perovskite aristo-type for x = 0.50 and 0.67 with randomly distributed vacancies. The Fe4+ content increases linearly in the oxidized samples up to x approximate to 0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0 less than or equal to x less than or equal to 0.90) which show decreasing Neel temperature and ordered magnetic moment with increasing x, while the Neel temperature is nearly constant at similar to 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500-600 K and 150-185 K. (C) 2000 Academic Press.