Martensitic and superconducting phase transitions in A15 compounds

Recent progress in the study of A15 compounds is reviewed by paying attention to the martensitic transition (MT) and the correlation between the MT and superconductivity (SC) in V3Si and Nb3Sn. The experimental results are summarised in order to reveal the characteristics of the MT and the correlation. These characteristics together with the electronic band structures calculated recently are compared with the theoretical results derived from Labbé and Friedel's, Gor'kov's and Г12-bands models for the origin of the MT. As the result, the Г12-bands model is shown to be consistent with various experimental results. The origin of the high T c, precursor phenomena of the MT, and ultrasonic attenuations are also discussed briefly.