LATTICE-DYNAMICS OF THE HIGH-TC SUPERCONDUCTOR LA2-PI-MXCUO4

The phonon dispersion curves, the one-phonon density of states and the specific heat of the high-T//c superconductor La//2// minus //xM//xCuO//4 have been calculated in the framework of a shell model. The zone center frequencies are classified according to their vibrational character and compared with the available IR and Raman data. A slight adjustment of the parameters obtained from the known interaction potentials of oxides with perovskite and rock salt structure yields agreement with the IR, Raman, specific heat, and inelastic neutron scattering data of the polycrystalline material.