Journal of Physics, Condensed Matter 2012-05-30

Rh2O3 versus IrO2: relativistic effects and the stability of Ir4+.

M-S Miao, R Seshadri

Index: J. Phys. Condens. Matter 24(21) , 215503, (2012)

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Abstract

Despite the wide-ranging applications of binary Rh and Ir oxides, their stability and trends in Rh and Ir oxidation states are not fully understood. Using first-principles electronic structure calculations, we demonstrate that the origin of the categorical stability of Ir(4+) is the relativistic contraction of the 6s orbital and, consequently, an expansion of 5d orbitals. Relativistic effects significantly stabilize Ir(4+)-containing metallic rutile IrO(2) over a wide range of O chemical potentials, despite the choice that Ir has of forming semiconducting corundum Ir(2)O(3). In contrast, Rh is found to display a wider stability range for corundum Rh(2)O(3) with Rh(3+) and a greater propensity for multiple oxidation states.