'Thermal' Kaiser's effect in YBa₂Cu₃O_7-X ceramic in the vicinity of 100-200 K by acoustic emission data

The acoustic emission (AE) has been measured during the thermal cycling of YBa₂Cu₃O_7-X ceramic samples through the 77-200K temperature range at a rate of about 0.7Ks^-1. AE signals have been detected in the vicinity of 100-168K. It has been established that the AE count rate exponentially increases and attains maxima at the third cycle and then exponentially decreases. In contrast, the AE temperature (T_AE) is equal to 113K at the first cycle and then decreases to minima at 100K at the third cycle and then increases again up to 168K at the seventh cycle. In suggesting a thermal activation process, both activation energies E _1-3 ≤ 0.016eV during 1-3 cycles and E_3-7 ≤ 0.032eV during 3-7 cycles have been calculated. Based on the calculated E value the equivalent thermal loading σ_l ≤ 133.12kPa (F_l ≤ 3.3N) has been calculated as well. This F_l is more than two orders of magnitude greater than the yield stress value for YBa ₂Cu₃O_7-X, so measured AE signals are due to arise from dislocations under thermal stresses. The behaviour of AE on 1-3 cycles is explained as both an annihilation between postsintering dislocations and dislocations arising due to anisotropic thermal expansion of the crystallographic lattice as well as the appearance of work hardening caused by the dislocations arising due to anisotropic thermal expansion of the crystallographic lattice on 3-7 cycles only, whereas the behaviour of T _AE is explained as the appearance of the 'thermal' Kaiser's effect during the thermal cycling.