ION-CHANNELING STUDIES OF LATTICE ANOMALIES WELL ABOVE T-C IN YBA2CU3O7-Y

Backscattering yields in the < 001 > axial channeling mode using D+ io ns have been measured for YBa2 Cu3O7-y single crystals with T-c=59K, 6 8K and 91K at temperatures between 40K and 295K. In 60 K-class YBa2Cu3 O7-y with significant anomalies associated with the spin gap, it is fo und that the channeling anomalies are observed at 130-140 K(T-pa) in a ddition to anomalies at T-c. The channeling anomalies at T-c follow to the shift of T-c, suggesting the phonon anomalies induced by the supe rconducting-gap opening. On the other hand, T-pa is found to be almost unchanged for varying T-c, although T-pa appears near the temperature where the spin gap is opened, This leads a question whether the chann eling anomalies at T-pa is directly related to the phonon anomalies in duced by the spin-gap opening. The existence of lattice instability is suggested as one of possible explanations for the anomalies at T-pa.