A comparison study of the Born effective charges and dielectric properties of the cubic, tetragonal, monoclinic, ortho-I, ortho-II and ortho-III phases of zirconia

摘要

Using density-functional perturbation theory, we systematically investigate the Born effective charges and dielectric properties of cubic, tetragonal, monoclinic, ortho-I (Pbca), ortho-II (Pnma) and ortho-III (Pca21) phases of ZrO2. The magnitudes of the Born effective charges of the Zr and oxygen atoms are greater than their nominal ionic valences (+4 for Zr and ?2 for oxygen), indicating a strong dynamic charge transfer from Zr atoms to O atoms and a mixed covalent-ionic bonding in six phases of ZrO2. For all six phases of ZrO2, the electronic contributionsεij∞to the static dielectric constant are rather small (range from 5 to 6.5) and neither strongly anisotropic nor strongly dependent on the structural phase, while the ionic contributionsεijionto the static dielectric constant are large and not only anisotropic but also dependent on the structural phase. The average dielectric constantεˉ0of the six ZrO2phases decreases in the sequence of tetragonal, cubic, ortho-II (Pnma), ortho-I (Pbca), ortho-III (Pca21) and monoclinic. So among six phases of ZrO2, the tetragonal and cubic phases are two suitable phases to replace SiO2as the gate dielectric material in modern integrated-circuit technology. Furthermore, for the tetragonal ZrO2the best orientation is [100].