High-precision equation of state data for TiO2 : A structural analog of SiO2

Abstract

The high-pressure response of titanium dioxide (${\mathrm{TiO}}_{2}$) is of interest because of its numerous industrial applications and its structural similarities to silica (${\mathrm{SiO}}_{2}$). We used three platforms---Sandia's Z machine, Omega Laser Facility, and density-functional theory-based quantum molecular dynamics (QMD) simulations---to study the equation of state (EOS) of ${\mathrm{TiO}}_{2}$ at extreme conditions. We used magnetically accelerated flyer plates at Sandia to measure Hugoniot of ${\mathrm{TiO}}_{2}$ up to pressures of 855 GPa. We used a laser-driven shock wave at Omega to measure the shock temperature in ${\mathrm{TiO}}_{2}$. Our Z data show that rutile ${\mathrm{TiO}}_{2}$ reaches 2.2-fold compression at a pressure of 855 GPa and Omega data show that ${\mathrm{TiO}}_{2}$ is a reflecting liquid above 230 GPa. The QMD simulations are in excellent agreement with the experimental Hugoniot in both pressure and temperature. A melt curve for ${\mathrm{TiO}}_{2}$ is also proposed based on the QMD simulations. The combined experimental results show ${\mathrm{TiO}}_{2}$ is in a liquid at these explored pressure ranges and is not highly incompressible as suggested by a previous study.