Study of the interatomic forces in the A15 superconducting compounds

The lattice dynamics of the A15 superconducting compounds have been investigated using a model in which the interatomic forces include, in addition to central forces, the angular forces of the type employed by de Launey. This model has been applied to Mo₃Si, Cr₃Si and V₃Si to investigate the phonon dispersion curves in the three symmetry directions of the Brillouin Zone. The force constants have been evaluated by fitting them to the measured values of the phonons at the zone centre. The calculated results are found to be in good agreement with the available experimental results. It has been inferred that the angular forces are not important for these compounds. The physical aspects for the same are discussed.