Structure and properties of ordered Li{sub 2}IrO{sub 3} and Li{sub 2}PtO{sub 3}

The structures of Li{sub 2}MO{sub 3} (M=Ir, Pt) can be derived from the well-known Li-ion battery cathode material, LiCoO{sub 2}, through ordering of Li{sup +} and M{sup 4+} ions in the layers that are exclusively occupied by cobalt in LiCoO{sub 2}. The additional cation ordering lowers the symmetry from rhombohedral (R-3m) to monoclinic (C2/m). Unlike Li{sub 2}RuO{sub 3} no evidence is found for a further distortion of the structure driven by formation of metal-metal bonds. Thermal analysis studies coupled with both ex-situ and in-situ X-ray diffraction measurements show that these compounds are stable up to temperatures approaching 1375 K in O{sub 2}, N{sub 2}, and air, but decompose at much lower temperatures in forming gas (5% H{sub 2}:95% N{sub 2}) due to reduction of the transition metal to its elemental form. Li{sub 2}IrO{sub 3} undergoes a slightly more complicated decomposition in reducing atmospheres, which appears to involve loss of oxygen prior to collapse of the layered Li{sub 2}IrO{sub 3} structure. Electrical measurements, UV-visible reflectance spectroscopy and electronic band structure calculations show that Li{sub 2}IrO{sub 3} is metallic, while Li{sub 2}PtO{sub 3} is a semiconductor, with a band gap of 2.3 eV. - Graphical abstract: The Li{sub 2}IrO{sub 3} and Li{sub 2}PtO{sub 3} were synthesized. Refinements are presented along with thermal and electrical properties, which are compared and contrasted with Li{sub 2}RuO{sub 3} when appropriate.