Novel gamma-phase of titanium metal at megabar pressures

Group IV transition metals titanium, zirconium, and hafnium are expected to transform from an ambient hexagonal close packed (hcp, alpha -phase) to a body centered cubic (bcc, beta -phase) at high pressures. This transition p ath is usually facilitated by the occurrence of an intermediate hexagonal p hase (distorted bcc, omega -phase). The existence of a bce phase in zirconi um and hafnium at high pressures has been known for the past ten years; how ever, its occurrence in titanium has been theoretically predicted but never observed. We report a novel unexpected transformation in titanium metal fr om an omega phase to an orthorhombic phase (distorted hcp, gamma -phase) at a pressure of 116 +/- 4 GPa.