Effects of solid solutions on the superconducting properties of Gd-Ba-Cu-O superconductors

摘要

The superconducting properties of the nominal Gd_(1+2x)Ba_(2+x)Cu_(3+x)O_(7-delta) (x = 0, 0.1, 0.2, 0.3, 0.4) single-domain bulks which consist of GdBa_2Cu_3O_(7-delta) (Gdl23), Gd_2BaCuO_5 (Gd211) and Gd_(1+y)Ba_(2-y)Cu_3O_(7-delta) have been investigated through magnetization and resistivity measurements. With increasing Gd211 content x, the trapped magnetic field reaches a maximum for the sample x = 0.2. The second peak in the critical current density J_c versus magnetic field B curve shifts toward the high magnetic regime for the sample x = 0.2 compared with that for the sample x - 0, but decreases to low magnetic field for the samples x > 0.2. Two superconducting transitions in resistivity rho_(ab) indicate that the low Tc clusters, i.e. Gd_(1+y)Ba_(2-y)Cu_3O_(7-delta) solid solutions, are interspersed in the GdBa_2Cu_3O_(7-delta) superconducting matrix. The delta T_C pinning resulting from the compositional fluctuations should be responsible for the enhancement of J_c and the trapped field for the sample x = 0.2.