An ab initio LAPW study of the α and β phases of bulk molybdenum trioxide, MoO3

Structure and electronic properties of the alpha and beta-MoO3, have been studied with periodic LAPW calculations. The structure and electronic properties of the alpha-MoO3 are in quite agreement with experimental and previous theoretical results. The oxide is partially ionic and the symmetrically bridging oxygens exhibit more ionic feature while the terminal oxygens are more covalent. The lattice scaling of the beta-MoO3 give results in excellent agreement with the reported experimental pseudo-cubic results. It has been found from density of states (DOS) that beta-MoO3 is not fully ionic system and some covalent contributions are still appreciable. These covalent contributions to the bonding appear derisory compared to the covalent contributions of the alpha phase. The beta-MoO3 --> alpha-MoO3 transformation is explained by metal off-center displacement toward O-1 (and a little less toward O-2) centers which is stabilized by an increase in covalency between the Mo and oxygen atoms. (C) 2005 Elsevier B.V. All rights reserved.