First-principles study of high pressure structure phase transition and elastic properties of titanium

We present a study of the structural phase transition and elastic properties of titanium (Ti) by using the projector augmented wave (PAW) within the Perdew-Burke-Ernzerhof (PBE) form of generalized-gradient approximation (GGA). The calculated phase transition omega -> gamma at ca. 116.5 GPa, which agrees well with the experimentally observed transition pressure of 116.0 +/- 4.0 GPa. However, other theoretical calculations are far from experimental value. We also find that the delta phase is not stable in the whole pressure range considered and phase transition from gamma to beta phase occurs at 162.4 GPa. This conclusion is in accordance with those of Joshi et al. and Vermal et al., but in disagreement with the experimental results of Vohra et al. and Akahama et al. Especially, the elastic properties of omega-Ti under high pressure are studied for the first time. We note that the compressional and shear wave velocities as well as the bulk B and shear moduli G increase monotonically with increasing pressure. By analyzing R-G/B, the brittle-ductile behavior of Ti is assessed. Polycrystalline elastic properties are also obtained successfully for a complete description of elastic properties. (C) 2010 Elsevier Masson SAS. All rights reserved.