ANOMALOUS LATTICE EXPANSION OF BI-BASED SUPERCONDUCTORS

The dependence of X-ray diffraction on temperature was measured to study the properties of thermal expansion and distortion of lattices in the Bi-system superconductors. Results show that the anomalous expansion of lattices in the Bi-based superconducting phases 2223 and 2212 exists both in the high and low temperature regions. In the high temperature region (230 is similar to 200 K), the anomalous expansion occurs at the same temperature for both the 2223 and 2212 phases. But in the low temperature region, the two phases have different anomalous temperatures (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 Mossbauer spectroscopy and internal friction, shows that the structural instability related with the softening and anomalous expansion of lattices occurs as a precursor effect to the onset of superconductivity.