Structure and properties of ordered Li2IrO3 and Li2PtO3

The structures of Li2MO3 (M=lr, Pt) can be derived from the well-known Li-ion battery cathode material, LiCoO2, through ordering of Li+ and M4+ ions in the layers that are exclusively occupied by cobalt in LiCoO2. The additional cation ordering lowers the symmetry from rhombohedral (R-3m) to monoclinic (C2/m). Unlike Li2RuO3 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 02, O-2, and air, but decompose at much lower temperatures in forming gas (5% H-2:95% N-2) due to reduction of the transition metal to its elemental form. Li(2)lrO(3) undergoes a slightly more complicated decomposition in reducing atmospheres, which appears to involve loss of oxygen prior to collapse of the layered Li(2)lrO(3) structure. Electrical measurements, UV-visible reflectance spectroscopy and electronic band structure calculations show that Li(2)lrO(3) is metallic, while Li2PtO3 is a semiconductor, with a band gap of 2.3 eV. (C) 2008 Elsevier Inc. All rights reserved.