Shock compression of niobium oxides from first-principles.

The equation of state and shock properties of the bulk niobium oxides NbO and NbO2 were investigated within the framework of density functional theory, with Mermin's generalization to finite temperatures. The shock Hugoniots for fully-dense and slightly porous NbO and NbO2 were predicted from canonical ab initio molecular dynamics (AIMD) simulations. The phase space was sampled along isotherms in the ranges 300 – 2500 K for NbO and 300 – 1200 K for NbO2, with densities ranging from 5.5 to 10.5 g/cm3 and 4.5 to 9.0 g/cm3, respectively. NbO and NbO2 isotherms show possible phase transitions above ∼ 60 GPa and ∼ 30 GPa, respectively. At low pressure, the effect of oxidation remains relatively limited according to the present AIMD simulations. [ABSTRACT FROM AUTHOR]