Shock compression of crystalline TeO2 to the high-pressure fluid regime: Insights from ab initio molecular dynamics simulations

The shock response of fully-dense and porous crystalline tellurium dioxide (TeO 2) to the high-pressure and high-temperature fluid regime was investigated within the framework of density functional theory with Mermin's generalization to finite temperatures. The principal and porous shock Hugoniot curves were predicted from canonical ab initio molecular dynamics (AIMD) simulations, with the phase space sampled along isotherms up to 80 000 K, for densities ranging from rho = 3 to 17 g/cm(3). The polymorphs investigated are alpha - TeO2 paratellurite ( P4(1)2(1)2), TeO2 cotunnite ( Pnma), and TeO2 post-cotunnite ( P2(1)/m). Based on the discontinuity found in the calculated U-s - u(p) slope of TeO2 post-cotunnite at a shock velocity of U-s similar or equal to 8.35 km/s and a particle velocity of u p similar or equal to 3.64 km/s, the shock melting temperature and pressure are predicted to be similar or equal to 6500 K and similar or equal to 170 GPa. Results from the AIMD simulations are in line with the static compression data of TeO2 paratellurite and cotunnite, and with the recent shock Hugoniot data for single-crystal alpha - TeO2 for pressures up to 85 GPa, obtained using the inclined-mirror method and the velocity interferometer system for any reflector combined with powder gun and two-stage light-gas gun.