Model phonon spectra and densities of states of Nb3Sn and Nb3Ge structures

Abstract

The e ciency of combining the concept of superspatial symmetry and the ideas of the lattice model for the calculation of the model phonon spectra of complex crystalline formations is shown. 3 + 3- dimensional bases, sets of modulation vectors and (4 × 4a × 4a) lattice model for the description of crystal structure are presented and calculations of model phonon spectra and state densities of Nb3Sn and Nb3Ge structures at di erent combinations of force constants are given. As a result of the analysis it is shown that at the choice of certain combinations of power constants, mainly α4, α5 and α6, it is possible to obtain phonon spectra with optical frequencies in 150- 240 cm−1 range, which correlates with the experimental data. However, the distribution of densities in the spectra of phonon states is signi cantly di erent, which may re ect the signi cant lability of the chemical bond in these compounds, despite the binary nature of their composition.