Phase transition and equation of state of paratellurite (TeO2) under high pressure

Abstract

The Hugoniot data for TeO2 single crystals were obtained for pressures up to ∼85 GPa along both the 〈100〉 (a-axis) and 〈001〉 (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun or two-stage light gas gun. The Hugoniot-elastic limit of TeO2 was determined to be 3.3–4.3 GPa along the c-axes. The shock velocity (Us) versus particle velocity (Up) relation for TeO2 shows a kink around Up = 1.0 km s−1, which suggests a phase transition completes at ∼26 ± 2 GPa. The Hugoniot relations of the low and high pressure phase are given by Us = 3.13(5) + 1.10(6)Up for Up < 1.0 km s−1 and Us = 2.73(9) + 1.49(5)Up for Up > 1.0 km s−1, respectively. First-principles geometry optimizations based on the generalized gradient approximation after Perdew, Burke and Ernzerhof method were also performed on TeO2. It suggested that a continuous structure distortion occurs up to 22 GPa, and the lattice parameters b and c abruptly increase and decrease at 22 GPa, respectively, indicating a first-order phase transition to the cotunnite structure phase. The equation of state of the cotunnite phase TeO2 is discussed based on the experimental and simulation results.