'Thermal' Kaiser's effect in YBa_2Cu_3O_(7-x) ceramic in the vicinity of 100-200 K by acoustic emission data

摘要

The acoustic emission (AE) has been measured during the thermal cycling of YBa_2Cu_3O(7-x) ceramic samples through the 77-200 K temperature range at a rate of about 0.7 K s~(-1). AE signals have been detected in the vicinity of 100-168 K. 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 (TAE) is equal to 113 K at the first cycle and then decreases to minima at 100 K at the third cycle and then increases again up to 168 K at the seventh cycle. In suggesting a thermal activation process, both activation energies E_(1-3) = 0.016 eV during 1-3 cycles and E(3-7) = 0.032 eV during 3-7 cycles have been calculated. Based on the calculated E value the equivalent thermal loading sigma_l = 133.12 kPa (F_l - 3.3 N) has been calculated as well. This F_l is more than two orders of magnitude greater than the yield stress value for YBa_2Cu_3O_(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.