Phonon density of states of superconducting Bi1.6Pb0.4Sr1.8 Ba0.2Ca2Cu3Oδ

Bi-based cuprates consist of at least three superconducting phases with very similar crystal structures. The general chemical formula for these phases can be written as Bi2Sr2Can-1CunO2n+4+y where n = 1,2 and 3 corresponds to the 2201 (TC=10 K), 2212 (TC = 80 K) and 2223 (TC = 110 K) phases, respectively. The high-TC (2223) phase is difficult to prepare in a single phase. Partial substitution of Pb for Bi enhances the growth of the 2223 phase. The Cu-O sheets are primarily responsible for the superconductivity in the HTSCs. It is well established that in conventional superconductors the coupling between electrons and phonons (collective vibrations) leads to charge carrier pairing, and hence to superconductivity. The role of this coupling in copper-oxide superconducting materials is still a subject of intense research efforts. Raman scattering experiments have demonstrated the coupling between the superconducting electrons and the phonons in HTSCs. In this way the inelastic neutron scattering may also be a powerful tool. No vibrational study either by Raman or INS method was performed so far on Bi(2223) compound. The paper presents new results obtained by means of the inelastic slow neutron scattering taken on a high resolution time-of-flight spectrometer at BER II reactor of BENSC, Berlin. (authors)