Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9: Syntheses, crystal structures and magnetic properties
Abstract
Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9 were prepared and characterized. Ba3CoSb2O9 was prepared in polycrystalline form by high-pressure (HP) high-temperature treatment of the hexagonal 6H polytype of Ba3CoSb2O9. Polycrystalline samples of Ba2SrCoSb2O9 were obtained at ambient pressure by a solidstate reaction method. Combined Rietveld refinements of X-ray and neutron diffraction patterns indicated that HP Ba3CoSb2O9 and Ba2SrCoSb2O9 both crystallize in a Fm (3) over barm cubic double perovskite A(2)BB'O-6 structure with formulae Ba-2(Sb0.83Co0.17)(Co0.5Sb0.5)O-6 and (Ba1.33Sr0.67)Sb(Co0.7Sb0.3)O-6, respectively. Electron diffraction results obtained for Ba2SrCoSb2O9 showed no sign of additional periodicity. Weiss temperatures extracted from high-temperature magnetic susceptibility data were. theta approximate to -113 K and -118 K for HP Ba3CoSb2O9 and Ba2SrCoSb2O9, respectively. HP Ba3CoSb2O9 displays a weak ZFC-FC magnetic irreversibilty below 8 K. Ba2SrCoSb2O9 exhibits a spin freezing at T-f approximate to 6 K, and mu SR and Sb-121 NMR data revealed a magnetic transition towards a disordered ground state.