Phonon Spectra of CU7GeSe5I and Ag7GeSe5I Crystals

Abstract

Model calculations of the phonon dispersion dependencies have been carried out for the CU7GeSe5I and Ag7GeSe5I superionic crystals. For the first time, within the framework of the superspace symmetry concept the CU7GeSe5I and Ag7GeSe5I crystals have been investigated and their (3+d)-dimensional model descriptions have been developed. The description of the models of the considered structures was reduced to the construction of the modulation vectors arrays, definition of the mass modulation functions, construction of the generalized dynamic matrix as a superposition of the dynamic matrices of monoatomic structures; and the eigenvalues of the dispersion dependencies of the single particle perturbations have been obtained for the high symmetry directions of the Brillouin zone. The dynamic matrices $D_{a\beta}(k+q_{i})$ of the protocrystals were calculated taking into account a certain number of the force constant of the influential coordination groups.