ANOMALOUS LATTICE EXPANSION OF BI-BASED SUPERCONDUCTORS

The dependence of X-ray diffraction on temperature was measured to stu dy the properties of thermal expansion and distortion of lattices in t he Bi-system superconductors. Results show that the anomalous expansio n of lattices in the Bi-based superconducting phases 2223 and 2212 exi sts both in the high and low temperature regions. In the high temperat ure region (230 is similar to 200 K), the anomalous expansion occurs a t the same temperature for both the 2223 and 2212 phases. But in the l ow temperature region, the two phases have different anomalous tempera tures (T(a)); however, they still obey the relation T(a) = T(C0) + is similar to 20 K. The present result, along with the observation of Mos sbauer spectroscopy and internal friction, shows that the structural i nstability related with the softening and anomalous expansion of latti ces occurs as a precursor effect to the onset of superconductivity.