INFLUENCE OF Y2BACUO5 PRECIPITATE SIZE ON FLUX-PINNING EFFECT IN MELT-TEXTURE-GROWTH YBA2CU3O7-Y

The measurements of the microstructure, M(H) hysteresis and M(t) relax ation have been carried out on two types df melt-textured YBa2Cu3O7-y samples: stochiometic Y1.8Ba2.4Cu3.4Ox (Al) and Y1.8Ba2.4Cu3.4Ox + 0.0 5 mol%Pt (A2). It was found that the size of Y2BaCuO5 (Y-211) precipit ates in A2 sample is smaller than that in Al sample; that the flux pin ning potential depth U-00 in the A2 sample is much larger than that in the Al sample; and that the normalized relaxation rate S value of the A2 sample is lower than that of the Al sample. The results show that the reduction of the size of Y-211 precipitate can result in the incre ase of the flux pinning strength.