Electronic structure of cubic and orthorhombic phases of ZrW2O8 -: art. no. 113110

ZrW2O8 has a negative thermal expansion, and exists in two crystalline forms. The stable cubic alpha phase transforms into an orthorhombic gamma-phase at a low pressure of 0.21 GPa. A further increase in pressure beyond 1.5 GPa can induce an amorphous phase. The band structures of both alpha and gamma phases of ZrW2O8 are studied using a first-principles method based on density-functional theory. alpha-ZrW2O8 has an indirect band gap of 2.84 eV, while gamma-ZrW2O8 has a direct band gap of 2.17 eV. The electronic structure and bonding are discussed in the context of atom-resolved and orbital-resolved partial density of states, the Mulliken effective charges, and the bond orders. It is shown that gamma-ZrW2O8 has a larger total crystal bond order than alpha-ZrW2O8, due to the formation of additional W-O bonds. For the alpha phase, the calculated bulk modulus of 63 GPa is found to be in good agreement experimental values.