Probing local site disorder in zirconate pyrochlores

Abstract

Structure disorder in pyrochlore oxides is critical to various physical properties such as radiation damage resistance and ionic conductivity, but the mechanism of atomic structural transitions of pyrochlores to their disordered phases is not well understood. Here we present the density functional theory calculations probing the local site disorder with respect to the oxygen migration and cation antisite for zirconate pyrochlores. Induced by the migration of 48f oxygen to the nearest vacant 8a site in the disordering process, the local pyrochlore structure tends to partially or fully transform to the weberite structure depending on the cation properties. The degree of such disordering can be characterized by the oxygen migration ratio. In A2Zr2O7 zirconate pyrochlores with an A cation radius less than Gd3+, no more than 25% of the critical oxygen migration ratio drives the systems to the most stable disordered phases. However, the disorder can hardly occur in the A2Zr2O7 with the A cation radius larger than Gd3+. The origin of such disordering is primarily attributed to a strong chemical preference of Zr atoms that adopt a 7-coordinated local environment and similar size of two cations. This study will provide new insight into the disordering mechanism of pyrochlores and may further inspire the design of these materials with tailored material properties.