Synthesis, Crystal Structure, and Properties of the Ordered Double Perovskite Sr2CoOsO6

Sr2CoOsO6, a new osmium based ordered semiconductor double perovskite was prepared by solid state synthesis from the respective binary oxides. Room temperature PXRD analysis shows the compound to be tetragonal [I4/m; a = 5.5503(1) angstrom and c = 7.9320(1) angstrom], whereas low temperature synchrotron data refinement has revealed a second monoclinic polymorph [I2/m; a = 5.4969(2) angstrom, b = 5.4979(2) angstrom, c = 8.0090(1) angstrom and = 90.527(1)degrees] with a fully ordered rocksalt arrangement of cobalt and osmium atoms over the perovskite B-sites. Heat capacity and magnetic measurements indicate that Sr2CoOsO6 shows antiferromagnetic ordering below T-N = 108 K followed by a second magnetic transition at T-2 = 65 K. It was shown that the change from the tetragonal to the monoclinic phase occurs at T-N.