High Oxygen Pressure and the Preparation of New Iridium (VI) Oxides with Perovskite Structure: Sr 2MIrO 6 ( M = Ca, Mg)
Ir(VI) in an octahedral coordination has been stabilized in Sr 2MlrO 6 ( M = Ca, Mg) oxides with an ordered perovskite structure by use of high oxygen pressure. The structure of Sr 2CaIrO 6 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 t32 ge0g electronic configuration of Ir(VI) leads to a high Néel temperature with 55 K ( M = Ca) and 80 K ( M = Mg). The samples are not metallic conductors.