TEMPERATURE AND COMPOSITION EVOLUTION OF THE PHONON DENSITY OF STATES IN (BA,K) (PB,BI,SB) O3 CERAMIC OXIDES

The neutron-weighted phonon density of states of the superconducting Ba0.6K0.4BiO3, BaPb0.75Bi0.25O3 and BaPb0.75Sb0.25O3 perovskites and their non-superconducting analogues, BaPbO3 and BaBiO3, have been measured by the neutron time-of-flight technique between 5 and 300 K. The spectra show very pronounced changes in the energies and intensities of the oxygen bending and breathing phonons, in sharp contrast to the more subtle situation encountered with the cuprate superconductors. There are also changes in the low-energy transfer region, reflecting the structural and electronic variations in the series. The results are consistent with the predictions of theoretical models for a primarily phonon-mediated mechanism for superconductivity.