Effect of changing microstructure of Y-Ba-Cu-O superconductors on the vortex motion under non-equilibrium thermal conditions

Repetition of cooling and heating of high-Tc superconductors is detected to be able to result in some change of their microstructure. A non-equilibrium experimental technique provides direct measurement of the velocity of vortex motion in high-Tc Y-Ba-Cu-O superconductors. Its value falls in the interval of 8.3 x 10-2 - 16.0 x 10-2 mm/s depending on the number of the cooling or heating cycles, to which the samples are submitted. The thermal cycling created homogenization of the specimen's microstructure, and is presumed to cause this phenomenon, decreasing the number and strength of pinning centers. This supposition is proved by X-ray diffractography and transmission electron microscopy. A simple irreversible thermodynamic theory is elaborated to describe the reason, direction and dissipative character of the vortex motion. (orig.)