Systematic ab initio structure simulations have been used to explore the high-pressure behavior of nitinol (NiTi) at zero temperature. Our crystal structure prediction and first-principles calculations reveal that the known $B19$ phase is dynamically unstable, and an orthorhombic structure (Pbcm) and a face-centered-cubic $B32$ structure $\left(Fd\overline{3}m\right)$ become stable above ∼4 and 29 GPa, respectively. The predicted, highest-pressure, $B32$ phase is composed of two interpenetrating diamond structures, with a structural topology that is quite distinct from that of the other phases of NiTi. Interestingly, the $B32$ phase shows an unusual semiconducting characteristic as a result of its unique band structure and the nature of $3d$ orbitals localization, whose expected synthesis pressure is accessible to current experimental techniques.

• Received 23 October 2017
• Revised 5 January 2018

DOI:https://doi.org/10.1103/PhysRevB.97.140104