High-pressure phase transitions in SnO2

In situ observations of the phase transition in SnO2 were carried out in both a multianvil and a diamond-anvil cell high-pressure apparatus using synchrotron radiation. The phase transition from the α-PbO2-type (space group: Pbcn) to the pyrite-type (space group: Pa-3) structure was observed at high pressures and high temperatures. The phase boundary between the α-PbO2-type and pyrite-type structures in the temperature range of 800–1500 K was found to be given by the relation P(GPa)=16.7(±0.5)−0.0021(±0.0015)[T(K)−1000]. The negative slope of the transition is consistent with the calculated phase boundary between the α-PbO2-type and pyrite-type structures of silica (SiO2). However, our results do not agree with the slope of the phase boundary of germanium dioxide (GeO2), which was reported to have a positive slope. The Birch–Murnaghan equation of state for the pyrite-type phase of SnO2 was determined from the experimental unit-cell parameters, with K0=307(±10)GPa and V0=128.1(±0.3)Å3 with the value of K0′ set to 4.