The detailed crystal and electronic structures of the cotunnite-type ZrO2

The detailed crystal and orbital-decomposed electronic structures of cotunnite-type ZrO2 have been investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation as well as taking into account on-site Coulomb repulsive interaction (GGA+U). The optimized structure shows that the OIOI and OIIOII anions are surrounded by an arbitrary tetrahedron of four Zr cations and an arbitrary pentahedron of five Zr cations, respectively, in turn, the Zr cation is surrounded by an arbitrary tetrakaidecahedron formed by nine oxygen ligands. Although one more Zr cation is coordinated to OIIOII, the larger bond lengths between OIIOII and its adjacent five Zr cations (dOII−ZrdOII−Zr) than those between OIOI and its adjacent four Zr cations (dOI−ZrdOI−Zr) makes density of states (DOS) of ss and three pp (pxpx, pypy and pzpz) states of the OIIOII anion driving down in lower energy region and driving up in higher energy region. No crystal-field splitting is observed between three pp (pxpx, pypy and pzpz) states of anions OIOI and OIIOII (between three pp (pxpx, pypy and pzpz) states and five dd (dxydxy, dyzdyz, dxzdxz, dz2dz2 and dx2-y2dx2-y2) states of cation Zr) is resulted from the arrangements of the surrounding cations (anions) do not have any symmetry. The additional covalent character upon Zr–O ionic bonds is attributed to the hybridization of itinerant Zr(5s) and less filled Zr(4d) states to the separated O(2s) and O(2p) states.