A new intermediate phase in compressed nitinol

Abstract

Both experimental and theoretical efforts have demonstrated that nitinol shows distinct polymorphism at diverse temperature or pressure, holding a promise for applications in many fields. However, there are still some unknown structure transformations under high pressures. Here, we performed simulations to investigate these compressed structures through the metadynamics method combing with first-principles calculations. Under rapid compression, the ambient cubic phase (Pm-3m) tends to transform into an orthorhombic phase (Pbcm), undergoing an interesting phase with tetragonal symmetry (P4/mmm). More analyses of kinetic barrier indicate that the intermediate P4/mmm structure locates at a local minimum of the potential energy surface, which is derived from the body centered cubic Pm-3m structure. The current studies enrich the crystal configuration and provide useful information for the structural evolution of this system.