Landau theory of the martensitic transition inA−15compounds

Abstract

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 $A-15\mathrm{}$ compounds. Pretransition elastic anomalies, softening of the [110] transverse ([$1\overline{1}0$] 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 ${\Gamma }_{12}$ optic mode does not go soft at the transition, though its frequency is expected to be temperature dependent right up to room temperature.