Structure and Magnetism of Pr_(1-x)Sr_xFeO_(3-#sigma#)

摘要

Crystal structure, redox, and magnetic properties for the Pr_(1-x)Sr_xFeO_(3-#sigma#) solid-solution phase have been studied. Oxidized samples (prepared in air at 900degC) crystallize in the GdFeO_3-type structure for 0<=x<=0.80, and probably in the Sr_8Fe_8O_(23)-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe~(3+)) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacnacies. The Fe~(4+) content increase linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is obsered for oxidized samples (0<=x<=0.90) which show decreasing Neel temperature and ordered magnetic moment with increasing x, while the Neel temperature is nearly constant at approx 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 usceptibility curves in the temperature ranges 500-600 K and 150-185 K.