LOW-TEMPERATURE INTERNAL-FRICTION SPECTRUM OF POLYCRYSTALLINE Y-BA-CU-O

The internal friction (IF) and the elastic modulus of polycrystalline YBa2Cu3Ox specimens have been measured as a function of the temperature between 80K and 300K in the kilohertz frequency range. IF spectrum shows three reproducible maxima at 90K, 115K and 220K respectively. The 90K IF peak is not related to the superconducting transition because it is still observed after high temperature annealings in vacuum, which lead to the disappearance of the superconductivity. The 115K peak is due to a relaxation mechanism, which can be interpreted by oxygen atom jumps within the basal Cu-O plane. The broad 220K maximum, which was also observed by ultrasonic measurements, seems to be affected by the sample preparation: sintering conditions. Finally, a frequency hysteresis has been observed in every superconducting sample, which accounts for an anomalous behaviour of the elastic modulus. © 1990.