Effect of silver concentration on the structure and acoustic properties of the HTS composite YBa2Cu3O<i>x</i>–Ag
Abstract
Acoustic properties and structure of YBa2Cu3Ox–Ag composites are investigated in a wide range of silver concentration (c = 0–100%). An analysis of x-ray diffraction data and of the behavior of the structure-sensitive peak of ultrasound absorption reveals that the initial HTS phase 1:2:3 does not undergo any significant change in the technologically important concentration range c ≤ 20 vol.% Ag. In samples with c ≥ 10 vol.% Ag, a new relaxation absorption peak is observed, whose amplitude increases with c. It is shown that the microscopic mechanism responsible for this peak is the low-temperature dislocation relaxation in crystalline silver. The concentration dependence of the effective velocity of longitudinal sound is obtained for this composite for the first time, and its nonmonotonic nature is established. It is found that the formation of intergranular silver layers of various thickness determines the variation of elastic and relaxation properties of granulated HTS composites to a considerable extent.