LATTICE-DYNAMICS OF YBA2CU3O7-CHI

The phonon dispersion curves and the one-phonon density of states of the high-Tc superconductor YBa2Cu3O7-x have been calculated in the framework of a shell model which has been based on short range overlap and long range Coulomb potentials. The parameters of these potentials have been determined from the measured phonon dispersion curves of BaTiO3 and other metal oxides. These potentials yield rather satisfactory agreement with the available IR and Raman data without any major adjustment of the potential parameters. The results of our calculation thus provide a solid basis for the discussion of the role of phonons for the high transition temperature and a guide for further experimental studies of the vibrational properties of this and related compounds.