Atmosphere-sensitive 225 K feature in internal friction of YBa2Cu3O7−δ

Abstract
The Young’s modulus and internal friction of YBa2 Cu3 O7−δ were measured from 280 to 80 K at 40 kHz using an ultrasonic composite oscillator technique. Three internal friction peaks intrinsic to the polycrystalline material which were observed at 105, 125, and 225 K disappeared when the sample was deoxygenated. Other structure in the internal friction between 220 and 280 K is ascribed to water vapor. The 225 K peak is reversibly eliminated on exposure to moist air. This is suggestive of internal friction at crystal surfaces or grain boundaries.