An Internal Friction and Frequency Study in YBa2Cu3O7-x

Measurements of anelastic relaxation in the kHz range have been conducted in YBa2Cu3O7-x between 300 and 60 K. Two peaks are observed around the superconducting transition temperature, at 110 K and just below Tc, and an additional maximum at - 160 K in the sample prepared with BaCO3. The previously reported phase transformation at Tt- 240 K is shown to give rise to hysteretic effects which are absent when thermal cycling is conducted above Tt. The possible relation of the presently studied phase transformation with the non-reproducible enhancement of Tc above 100 K is discussed.