ANOMALOUS VARIATION OF THE RECOIL-FREE FRACTION OF EU-151 NUCLEUS IN EUBA2CU3O7-X AROUND THE SUPERCONDUCTING TRANSITION-TEMPERATURE

Mossbauer spectra of the superconductor EuBa2Cu3O7-x are measured at various temperatures (83 to 120 K) and the effective absorber thickness is calculated from the experimental spectra. The temperature variation of the recoil-free fraction of the Eu-151 nucleus in EuBa2Cu3O7-x is obtained. An anomaly in the temperature dependence of the recoil-free fraction of the Eu-151 nucleus in the superconductor EuBa2Cu3O7-x is found around the superconducting transition temperature. This may provide evidence of softening of lattice vibrations about the Eu atom in the crystal in the normal state-superconducting state transition process of the Eu-Ba-Cu-O system.