Phonon Dispersion in V₃Si

Abstract

The phonon frequencies of V3Si along the principal symmetry directions are calculated for a two band model from the microscopic dielectric screening approach. The d-electrons are approximated by a 6, band without interchain coupling. For the electron-ion interaction a local Heine-Abarenkov pseudopotential is used, with parameters very similar to those given before for V and Si. Most of the anomalies seem to arise from the presence of three orthogonal sets of chains of A atoms in the A15 structure which may give rise to planar Fermi surfaces [l6] and to sharp and narrow peaks in the electronic density of states [17 to 191. If the Fermi level falls close to one of these peaks all physical properties may become strongly temperature-dependent, and the resulting high elec-

Clebsch-Gordan coefficients for M x M in beta tungsten

“…Achar and Barsch [14] developed a theory of the phonon dispersion relations for compounds with A-15 structure, in particular V3Si and Nb3Sn. The results exhibit the observed softening of the TA mode in [110], and of the LA mode in [100] direction, leading eventually to a lattice instability.…”

“…Theories of structural phase transitions, applied to A-15 compounds, were proposed by Birman [7] and Gorkov [8] and discussed in [9][10][11][12][13]. In several compounds with the A-15 structure the phonons at the M point of the Brillouin zone become soft leading to lattice instability and eventually to a distortive phase transition [14].…”

Selection rules for the double space group of the beta-Wolfram structure

“…Powers TABLE V TABLE VI TABLE VII correspond to the frequency of occurrence ci of the given irreducible representation. In tables XII and XIII we summarize in the upper part, the notations of the single-valued representations and in the lower part, those of the spinor representations for the symmetry points r, R, M and X, according to various authors [47][48][49][50][51][52].…”

Clebsch-Gordan coefficients for X x X and R x R in beta tungsten

“…In several compounds of the A-15 structure the phonons become soft at the M point leading to the lattice instability and eventually to a distortive phase transition [10].…”