Effect of ion-vacancies and partial element substitutions on flux pinning in YBa/sub 2/Cu/sub 3/O/sub 7- delta /

It is found that at 77 K the existence of Y, Ba, Cu and O vacancies enhances the flux pinning in varying degrees, and among them the vacancies have the highest enhancement of flux pinning. The Ba existence of Cu vacancies only improves the flux pinning under lower field. The pinning effect resulting from partial substitutions of rare earth elements with various atomic radii and magnetic moments for Y in Y/sub 1-x/M/sub x/Ba/sub 2/Cu/sub 3/O/sub 7- delta / (M=Gd, Eu, Sm) is also studied. The results show that the pinning strength increases with increasing the atomic radius of M, and the magnetic moment seems absent. These defects sometimes have different behaviors in higher fields than in lower fields. Possible pinning mechanisms are discussed.<>