High oxygen pressure and the preparation of new iridium (VI) oxides with perovskite structure: Sr₂MIrO₆ (M = Ca, Mg)

Ir(VI) in an octahedral coordination has been stabilized in Sr₂MlrO₆ (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 t³_2ge⁰_g 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.