EVIDENCE FOR LARGE STATIC AND DYNAMIC DISTORTIONS IN HIGH T-C SUPERCONDUCTING YBA2CU3O7-DELTA CRYSTALS OVER A WIDE TEMPERATURE-RANGE

Large deviations from the expected atomic thermal vibrational amplitud e in Cu-O rows in a YBa2Cu3O7-delta (T-c = 92.5 K) crystal have been o bserved in a wide temperature range (300-30 K) by ion channeling. In c ontrast, Y-Ba as well as Cu-O rows in nonsuperconducting deoxygenated YBa2Cu3O6.2 specimens show a normal decrease in the atomic vibrational amplitude as the sample temperature is lowered. These anomalous resul ts in the YBCO superconductor provide a clear indication of uncorrelat ed static and dynamic distortions associated with Cu-O rows. Possible implications of these structural changes are discussed.