Solid-Solid Transitions in Titanium and Zirconium at High Pressures

Abstract

The body-centered cubic to hexagonal close-packed transformations in titanium and zirconium have been studied by means of differential thermal analysis at pressures in the range 0-65 kbar and at cooling and heating rates of 3-5\ifmmode^\circ\else\textdegree\fi{}C/sec. The transitions occurred at different temperatures upon heating and upon cooling and these hysteresis intervals did not appear to vary much with increasing pressure and/or contamination. Alloying with the tantalum containers and consequent lowering of the transition temperatures was unavoidable in most of the experiments. The Ti transition decreases only slightly in temperature with increasing pressure; a zero pressure volume change of less than 0.3% is suggested. The Zr transition exhibits a slope of about -.24\ifmmode^\circ\else\textdegree\fi{}C/kbar until a new transition is encountered near 58 kbar; the transition from body-centered cubic to the new Zr polymorph is without much hysteresis, and the phase boundary exhibits a slope of about 0.6\ifmmode^\circ\else\textdegree\fi{}C/kbar. Discontinuities of about 17% in resistance at room temperature are detected near 51-59 kbar for Zr and 80-90 kbar for Ti, there being a decrease for Zr and an increase for the resistance of Ti.