EFFECT OF CHANGING MICROSTRUCTURE OF Y-BA-CU-O SUPERCONDUCTORS ON THEVORTEX MOTION UNDER NONEQUILIBRIUM THERMAL CONDITIONS

Repetition of cooling and heating of high-T-c superconductors is detec ted 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-TcY-Ba-Cu-O superconductors. Its va lue falls in the interval of 8.3 x 10(-2) - 16.0 x 10(-2) mm/s dependi ng on the number of the cooling or heating cycles, to which the sample s are submitted. The thermal cycling created homogenization of the spe cimen's microstructure, and is presumed to cause this phenomenon, decr easing 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.