ATOMIC POSITIONAL DISORDER, PHONON-SPECTRUM, AND MOLECULAR-DYNAMICS SIMULATION OF TL2CABA2CU2O8 AND TL2CA2BA2CU3O10

The nature of the atomic positional disorder in the high-temperature superconducting ceramic oxides Tl2CaBa2Cu2O8 (Tl 2:1:2:2) and Tl2Ca2Ba2Cu3O10 (Tl 2:2:2:3) is studied with the help of an ionic-type interatomic potential and molecular-dynamics computer simulations. The pair distribution function and the phonon spectrum are calculated using this model and compared with results of neutron-scattering experiments on Tl 2:1:2:2. Calculated results on the partial pair distribution function, partial phonon density of states, mean square atomic vibrational amplitudes, and lattice specific heat are also presented.