Noble-metal chalcogenides are known as both electronic and ionic conductors. Physics in superionic conductors is investigated on the basis of the idea of elementary excitations. First, the semiconducting properties of noble-metal chalcogenides are investigated by preparing the full Hamiltonian for conduction electrons and phonons. The influence of electron interactions on the longitudinal acoustic wave frequencies and the matrix element for the electron-phonon interaction are investigated. Three cases of omega>>k upsilon(F), omega

Keywords:Noble-metal chalcogenides;Elementary excitations;Electronic and ionic conductors;Structure factor;f-sum rule