Exploring the Mechanism of Phase Transitions between the Hexagonal Close-Packed and the Cuboidal Structures

By introducing appropriate lattice parameters for a bilattice smoothly connecting the hexagonal close-packed (hcp) structure with the cuboidal structures, namely the body-centered cubic (bcc) and the face-centered cubic (fcc) lattices, we were able to map out the minimum energy path for a Burgers-Bain type of phase transition. We demonstrate that for three different models applied, i.e., the kissing hard-sphere model, the Lennard-Jones potential, and density functional theory for metallic lithium, the direct transition path is always from hcp to fcc, with a separate path leading from fcc to bcc. This resolves, at least for the models considered here, a long-standing controversy regarding whether or not fcc acts as an intermediate phase in martensitic types of phase transitions.