Observation of high-pressure bcc phase of titanium at 243 GPa

In this study, the pressure-induced phase transition of the 3d transition metal titanium (Ti) has been investigated at pressures up to 290 GPa at room temperature using an x-ray diffraction technique with a micro-beam. From the analysis of powder x-ray diffraction patterns, the high-pressure δ phase (orthorhombic, Cmcm) was found to transform to the β phase (body-centered cubic: bcc, Im3m) at 243 GPa. Although the volume reduction at this phase transition was less than 1%, the coexistence of the δ phase suggests that the transition is of the first order. The isothermal bulk modulus at zero pressure, B0, and the pressure derivative of B0, B0′, were estimated to be 125(2) GPa and 3.46(6) GPa, respectively, by least squares fitting to the Vinet equation of state based on the P–V data of the δ and β phases. This transition to the bcc phase verified predictions from theoretical studies and demonstrated the systematics of the pressure-induced structural phase transition in transition metals.