Dynamic study of oxygen relaxations in YBa2Cu3O7-δ

It is well known that the properties of high-Tc superconducting materials depend strongly on the oxygen atoms (concentration and structural configuration). Consequently, understanding the oxygen mobility on an atomic scale becomes very important. This work presents the study of the oxygen mobility by means of internal friction measurements. Two energy dissipation peaks, which are closely related to the oxygen concentration, have been observed at 115 K (in the kilohertz frequency) and 510 K (in the low frequency range) respectively. Both of them are relaxation peaks. The first, at low temperature, (PL) has an activation energy HL = 0.17 ev. The second, at high temperature, (PH) has an activation energy HH = 1.10 ev. Both have frequency factors in the order of ∼ 1012 sec-1. Annealing the specimen in vacuum shows that the heights of both peaks decrease continuously as the annealing temperature is increased. This study of the relaxation strength reduction during annealing has been compared with measurements of oxygen loss (by weighing the specimen), electrical resistivity, and X-ray diffraction. Peak relaxation strengths are well correlated with the oxygen loss. Two relaxation models, which are both due to oxygen atoms movement within the basal Cu-O plane, could explain these two internal friction peaks. (orig.)