MOSSBAUER STUDY OF HIGH-TEMPERATURE SUPER CONDUCTORS AND RELATED-COMPOUNDS

Fe-57, Sn-119 and Eu-151 Mossbauer spectroscopy was used to study the chemical structure, phonon mode changes and low temperature phase tran sformation around the T(c) as well as suppression of superconductivity in high temperature superconductors and related compounds. Anomalous temperature dependent changes in the total Fe-57 spectral area fractio n and in the Mossbauer line shift were simultaneously found around the T(c) in a (EuBa2(Cu0.99Fe0.01)3O7-d)-Fe-57 superconductor. These anom alous changes were attributed to phonon softening and low temperature phase transformation occurring around the superconducting transition. Significant differences were observed between the Fe-57 Mossbauer spec tra of superconducting (EuBa2(Cu0.99Fe0.01)3O7-d)-Fe-57 and the isostr uctural (PrBa2(Cu0.99Fe0.01)3O7-d)-Fe-57 which is non-superconducting. The differences were interpreted in connection with the suppression o f superconductivity (by hole filling or hybridization of Pr, Cu and O states) in the Pr-containing compound. The unusually high isomer shift value observed in the Pr-containing material can give an evidence for the charge transfer mechanism between the Cu(1) chains and the Cu(2) planes and for its role in the suppression of superconductivity.