HIGH OXYGEN-PRESSURE AND THE PREPARATION OF NEW IRIDIUM(VI) OXIDES WITH PEROVSKITE STRUCTURE - SR(2)MIRO(6) (M=CA, MG)

Ir(VI) in an octahedral coordination has been stabilized in Sr(2)MIrO(6) (M = Ca, Mg) oxides with an ordered perovskite structure by use of high oxygen pressure. The structure of Sr2CaIrO6 depends strongly on the oxygen pressure and reversibly returns to the original structure according to the heat treatment applied. The oxidation state of iridium in each compound is determined by chemical titration and is correlated with the structural factors and the covalency of M-O bonds. The t(2)(3)e(g)(0) electronic configuration of Ir(VI) leads to a high Neel temperature with 55 K (M = Ca) and 80 K (M = Mg). The samples are not metallic conductors. (C) 1995 Academic Press, Inc.