Phase transitions in the SrSnO3-SrFeO3 solid solutions:: X-ray diffraction and Mossbauer studies

SrSn1-xFexOy (0less than or equal toxless than or equal to1) oxides were prepared by conventional solid-state reaction in air using high-purity (greater than or equal to99%) SrCO3, SnO2 and Fe(C2O)(2) . 2H(2)O at elevated temperatures of 1300degreesC for 24 It and furnace cooled. Samples obtained from 1300degreesC were annealed at 620degreesC for 2 days and quenched in liquid nitrogen (LN). Powder XRD analysis by Rietveld refinement and Fe Mossbauer spectroscopy measurements were employed to characterize synthesized perovskites. Samples obtained from furnace cooled and LN quenched undergo two compositionally driven phase transitions, which are supposed to be of second order. The x = 0-0.3 members crystallize in orthorhombic parent SrSnO3 structure (Space group Pbnm), whereas samples x = 0.4-0.9 have a simple cubic perovskite cell and end-member SrFeO2.74 Composition crystallize orthorhombic structure (Space group Cmmm). The composition of the first phase transition (x approximate to 0.3) is slightly shifted to higher x with decreasing annealing temperature. Mossbauer data show that the Fe4+/Fe-tot ratio is depending on composition under constant synthesis conditions. The phase compositions have been discussed in terms of ternary solid solution of compounds SrSnO3-SrFeO2.74-SrFeO2.5 superior to a simple binary solid solution (SrSno(3)SrFeO(3)). (C) 2003 Elsevier Inc. All rights reserved.