Landau theory of the martensitic transition in A-15 compounds

Based on Gorkov's physical model of a Peierls-like charge-density-wave- driven transition, a Landau theory has been formulated for the structural phase transition in the A-15 compounds. Pretransition elastic anomalies, softening of the [110] transverse ([110] polarized) phonon, sublattice distortions, variation of transition temperature with stress, and alloying and other effects have been accurately predicted, and a detailed comparison is made with experimental results. Central peaks in neutron scattering are shown to be nondynamic in nature and no pretransition forbidden (300) reflection is predicted. The 12 optic mode does not go soft at the transition, though its frequency is expected to be temperature dependent right up to room temperature.