High-pressure phase transitions and melt structure of PbO2: An analog for silica

In situ x-ray diffraction measurements and inverse Monte Carlo simulations of pair distribution functions were used to study the structural response of PbO2 under pressure and to characterize the local structure of liquid PbO2. Two phase transitions are observed upon room-temperature compression of crystalline PbO2 up to similar to 65 GPa. The starting mixture of rutile structured beta-PbO2 and orthorhombic alpha-PbO2 undergoes a transition to a ZrO2-type orthorhombic phase with space group Pbca at similar to 21 GPa. Above 42 GPa, the Pbca phase transforms to a cotunnite-type phase with space group Pnam. In this paper, we also report short-range order in liquid PbO2, showing similar to 8-9-fold and 4-5-fold coordination around Pb and O atoms, respectively.