Mössbauer and X-ray investigations of YBa2−x Sn x Cu3O7−δ superconductors

Mössbauer spectra of YBa_2?x Sn _x Cu₃O_7?δ compounds withx=0.2 and 0.3 have revealed two components, both with isomer shifts corresponding to 4⁺ valency for Sn. The temperature dependence of the area of only one component shows an anomaly near the superconducting temperature for both samples, thus suggesting anisotropic behaviour for the lattice rigidity. In the case ofx=0.2 sample X-ray diffraction studies further indicate similar anomaly in the orthorhombic strain. It is concluded that such anomalies are precursors for the superconductivity to occur in these compounds.