A study of the crystal structures and the phase transitions of Sr2FeSbO6, SrCaFeSbO6 and Ca2FeSbO6 double perovskite oxides

Sr2FeSbO6, SrCaFeSbO6 and Ca2FeSbO6 with the double perovskite structure have been synthesized by the conventional solid state reaction process. The crystal structures and phase transitions at low and high temperature were determined from Rietveld refinements of X-ray and neutron powder diffraction data. Sr2FeSbO6 crystallizes at room temperature in a monoclinic system having a space group I2/mI2/m and not P21/nP21/n space group as was previously reported. The crystal structures of SrCaFeSbO6 and Ca2FeSbO6 are described with the P21/nP21/n space group. All compounds show partial order of the B-site Fe and Sb cations, with degree of ordering of 89% for Sr2FeSbO6 and 94% for SrCaFeSbO6 and Ca2FeSbO6.