High-pressure phases of titanium: First-principles calculations

Abstract

We investigate through first-principles calculations the controversial observation of the high-pressure orthorhombic ($\ensuremath{\gamma}$ and $\ensuremath{\delta}$) phases of titanium. Our calculations predict the transition sequence $\ensuremath{\omega}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\beta}$ under pressure, and reveal that the $\ensuremath{\delta}$ phase is elastically unstable under isotropic compression. We attribute its observation to nonhydrostatic stresses present in the diamond-anvil cell experiments. We find the $\ensuremath{\gamma}$ phase to be stable in the $102--112\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ pressure range, with the upper limit of this pressure range increasing under nonhydrostatic conditions.