ANOMALOUS BEHAVIOR OF THERMAL VIBRATIONS OF ATOMS AS A RESULT OF THE PHASE-TRANSITION OF TL2BA2CACU2O8 SINGLE-CRYSTALS TO THE SUPERCONDUCTING STATE

An x-ray diffraction analysis reveals that structural parameters of a (Tl0.93Cu0.07)2Ba2.(Ca0.88Tl0.12) Cu2O8 single crystal with T(c) = 100 K behave in an anomalous way as a result of a phase transition to the superconducting state. The anomalous temperature dependence is seen p articularly clearly in parameters of thermal vibrations of atoms. It t hus becomes possible to draw conclusions about the changes in the vale nce state and the chemical bonds (i.e., the electronic structure) of a toms in the crystal upon the phase transition. Substantial changes in the phonon spectrum in the course of this phase transition are indicat ed.