First-principles equation of state and phase stability of niobium pentoxide

Niobium pentoxide is a polymorphic wide-gap semiconductor with good dielectric properties that make it an important material in technological applications. In spite of its significance, there are not theoretical studies of its phase stability and polymorphism. We have investigated the energetics and phase stability of several phases of Nb2O5 under pressure. The equation of state, the isothermal bulk moduli and the equilibrium crystal structures have been calculated from first-principles density functional theory for pressures up to 100 kbar. The equation of state reveals that the stable crystalline structure at zero pressure is the H phase, then, a crystallographic phase transition takes place at 0.24 kbar to the B phase. Additionally, it is shown that in the pressure range studied the B phase remains as the sole high-pressure stable phase.