Atomic scale mechanism for the Ge-induced stabilization of the tetragonal, very high-kappa, phase of ZrO(2)

Using x-ray absorption fine structure aided byab initiostructural simulations we demonstrate the atomic scale mechanism responsible for the stabilization of the otherwise unstable and very high-j tetragonal phase of ZrO2by the incorporation of Ge atoms. In tetragonal ZrO2the cation has a split first coordination shell formed by eight oxygen atoms. We provide a direct experimental proof that when Ge is incorporated in the oxide, four of the eight O atoms collapse towards Ge giving rise to a local structure strongly reminiscent of that found in quartz-like GeO2, thus stabilizing the tetragonal phase.