Alpha to omega martensitic phase transformation pathways in pure Zr

Abstract

Abstract This first principles study attempts to find the lowest enthalpy barrier transformation pathway (TP) for pressure induced α → ω transformation in pure Zr by systematically studying TPs suggested experimentally along with TPs generated from symmetry analysis. We find that symmetry generated pathways and model pathways given from experimental inputs essentially outline the same subset of possible pathways. The most favorable TP, comprising of smaller strains and atomic shuffles compared to others, has a C2/c as a common space group along the TP with enthalpy barrier of 22 meV/atom at 0 K. It is evident from the study that the softening of shear elastic constant C44 and Γ point transverse optical phonon frequency as a function of pressure in α-Zr are associated with change in effective potential landscape for the E2g phonon at Γ point of the Brillouin zone. The calculated electronic band structure as a function of pressure and E2g phonon mode shows a similar topological change in the band structure which drives this transformation.