Ab initio prediction of ordered ground-state structures in ZrO2 -Y2 O3

A coupled cluster expansion was used to direct an ab initio search for stable ordered structures on the cubic fluorite lattice across the ZrO2 -Y2 O3 composition range. The energies of 453 arrangements of (Zr, Y) cations and (O, vacancy) anions on the fluorite lattice were calculated by using density functional theory (DFT) in the generalized gradient approximation. These DFT energies were used to construct a coupled cluster expansion that allowed the search for possible T=0 K ground-state structures through ∼ 105 cation/anion configurations. Our approach correctly identifies the experimentally observed compound Zr3 Y4 O12 and also predicts an as-yet-unobserved ordered structure with Zr4 Y2 O11 stoichiometry. In the latter structure, vacancies are at second nearest neighbors from yttrium and every Zr has seven oxygen first nearest neighbors. The Zr-O bond lengths and oxygen coordination around Zr in the Zr4 Y2 O11 ground state are nearly the same as those in monoclinic ZrO2. We also predict structures at Zr5 Y2 O13 and Zr6 Y2 O15 that are stable with respect to cubic ZrO2 but metastable with respect to monoclinic ZrO2.