Disorder in Ho<sub>2</sub>Ti<sub>2−x</sub>Zr<sub>x</sub>O<sub>7</sub>: pyrochlore to defect fluorite solid solution series
Devon Drey, Eric C. O’Quinn, Tamilarasan Subramani, Kristina Lilova, Gianguido Baldinozzi, Igor M. Gussev, Antonio F. Fuentes, Jöerg C. Neuefeind, Michelle Everett, David Sprouster, Alexandra Navrotsky, Rodney C. Ewing, Maik Lang
Abstract
. However, the extensive short-range ordering determined from the structural analysis strongly suggests that the entropies of mixing must be far less positive than implied by the random mixing of a regular solution. We propose a local disordering scheme involving the pyrochlore 48f to 8a site oxygen Frenkel defect that creates 7-coordinated Zr sites contained within local weberite-type coherent nanodomains. Thus, the solid solution is best described as a mixture of two phases, with the weberite-type nanodomains triggering the long-range structural transformation to defect fluorite after accumulation above a critical concentration (50% Ti replaced by Zr).