title: Rh2O3 versus IrO2: relativistic effects and the stability of Ir4+.
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.
authors.affiliation: Materials Department, University of California, Santa Barbara, CA 93106, USA. miaoms@mrl.ucsb.edu
authors.forename: M-S
authors.initials: MS
authors.lastname: Miao
authors.forename: R
authors.initials: R
authors.lastname: Seshadri
mesh_terms: D003198:Computer Simulation; D007495:Iridium / Q000737:chemistry*; D008956:Models, Chemical; D044367:Phase Transition; D012211:Rhenium / Q000737:chemistry*
chemical_list: C044458:iridium oxide; C015428:perrhenate; D007495:Iridium; D012211:Rhenium