Anomalous Lattice Expansion of Bi-based Superconductors

<正> The dependence of X-ray diffraction on temperature was measured to studythe properties of thermal expansion and distortion of lattices in the Bi-system superconduc-tors.Results show that the anomalous expansion of lattices in the Bi-based superconductingphases 2223 and 2212 exists both in the high and low temperature regions.In the high tem-perature region（230～200K）,the anomalous expansion occurs at the same temperature forboth the 2223 and 2212 phases.But in the low temperature region,the two phases havedifferent anomalous temperatures（Ta）;however,they still obey the relation Ta=Tco+～20K.The present result,along with the observation of M（o|¨）ssbauer spectroscopy and internalfriction,shows that the structural instability related with the softening and anomalous ex-pansion of lattices occurs as a precursor effect to the onset of superconductivity.