Anelastic Effects in YBa ₂ Cu ₃ O 7-δ : A Study of the Point Defect Relaxation Observed for 0.6 < δ < 1

The internal friction and Young's modulus of YBa 2 Cu 3 O 7-δ have been measured between 4 K and 300 K for δ ≃ 0 and 0.6 < δ < 1. A point defect relaxation process with an activation energy of 0.1 eV occurs in the tetragonal samples. It is found that the number of relaxing entities vanishes when the oxygen concentration is increased and when the thermal treatment allows oxygen ordering in the CuO plane. The relaxation might be attributed to some oxygen atoms in this plane which have formed pairs, or which are isolated but trapped by defects.