Elastic instability of bcc cobalt

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Abstract
General-potential linearized-augmented-plane-wave calculations of the elastic properties of body-centered cubic Co are presented. The bcc structural phase of Co, which is not found in nature, is calculated to be unstable with respect to a volume-conserving tetragonal distortion. The total energy of body-centered tetragonal Co decreases monotonically as the c/a ratio is varied from 1, which corresponds to the bcc structure, to √2 , which corresponds to the face-centered-cubic structure. This means that bcc Co is not a true metastable phase of bulk Co and suggests that the existing samples of bcc Co that have been grown in the laboratory are stabilized by interactions with the substrate and/or defects.