MARTENSITIC-TRANSFORMATION OF CA

At room temperature Ca undergoes a pressure-induced structural transformation at 20 GPa from the fcc structure into the more open packed bcc. We investigate a distortion model for this transformation that differs from the Bain mechanism usually invoked to describe this transformation and consists of a variant of the Burgers mechanism for the hcp bcc transformation. It is shown that the Bain mechanism is a specific case of this more general triclinic distortion, and therefore that a path in this larger parameter space provides a different energy route when compared with that derived from the tetragonal Bain strain, which is lower in energy at some points. This finding is particularly relevant for future studies of temperature-induced fccbcc transformations. Our first-principles total-energy local-density-approximation study is accomplished by using the full-potential linear-augmented-plane-wave method. © 1990 The American Physical Society.