Structural transition in A-15 compounds: Possible Landau theory descriptions

A comparison is made of Landau theories of the martensitic transition in A-15 compounds involving direct coupling of the electronic order parameter to the lattice dilation (as in the Labbe-Friedel model) or coupling due to pairing of transition-metal atoms (as in Gorkov's Peierls-gap model worked out in a previous paper). It is shown that the predictions of the two phenomenological (as distinguished from microscopic) models in respect to existing experimental results are identical in form. Consequently, on the basis of current data, the A-15 compounds are amenable to a generalized Landau description involving either or both types of couplings. Tests of microscopic models based on either or both mechanisms are proposed.