Synthesis, Crystal Structure, and Properties of the Ordered Double Perovskite Sr 2 CoOsO 6

Sr 2 CoOsO 6 , 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 [ I 4/ m ; a = 5.5503(1) Å and c = 7.9320(1) Å], whereas low temperature synchrotron data refinement has revealed a second monoclinic polymorph [ I 2/ m ; a = 5.4969(2) Å, b = 5.4979(2) Å, c = 8.0090(1) Å and γ = 90.527(1)°] with a fully ordered rocksalt arrangement of cobalt and osmium atoms over the perovskite B ‐sites. Heat capacity and magnetic measurements indicate that Sr 2 CoOsO 6 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 .