MÖSSBAUER STUDY OF LATTICE DYNAMICS OF HIGH Tc SUPERCONDUCTORS

Abstract

Many strong-coupled superconductors have anomalous phonon properties. These anomalies manifest themselves as unusually soft modes, sometimes of a rather localized nature, or as anharmonic effects giving rise to hardening of certain modes at high temperatures. A study of lattice and electronic properties of high Tc Chevrel and P d ~ ~ s n ~ H superconductors has been made by means of the ll9Sn Mossbauer effect. In the high Te, high He2 superconductor SnM06Ss, the lattice is found to be anisotropic and anharmonic at the Sn site [I]. The degree of anharmonicity is large and obviates the use of perturbation treatments based on harmonic models. The results indicate that the phonon spectrum includes a strong tin resonance mode that hardens rapidly with increasing temperature. (Recent inelastic neutron scattering measurements are in agreement with this result [2]) . The impurity theory of Mannheim [3] has been applied to the results of our studies of the lattice dynamics of 1 lgSn in Pd. This study further corroborates the importance of nearest neighbor force constant changes and demonstrates the conditions for splitting a localized mode peak out of the host phonon spectrum. We have also studied the lattice dynamics of ll9Sn in the NaC1-type superconductor Pdo.99Sno.olH0,s. The addition of hydrogen has a marked effect on the electronic properties. We find a softening of the low energy tin modes and a hardening of the localized mode peak on hydriding. These results indicate softening of the Pd acoustic modes and the presence of a strong Sn-H interaction. (*) Based on work supported by the National Science Foundation and the U. S. Energy Research and Development Administration.