Effects of solid solutions on the superconducting properties of Gd–Ba–Cu–Osuperconductors

Abstract

The superconducting properties of the nominalGd1+2xBa2+xCu3+xO7−δ (x = 0, 0.1, 0.2, 0.3, 0.4) single-domain bulks which consist ofGdBa2Cu3O7−δ (Gd123),Gd2BaCuO5 (Gd211)and Gd1+yBa2−yCu3O7−δ, have been investigated through magnetization and resistivity measurements. With increasing Gd211content x, the trapped magnetic field reaches a maximum for the samplex = 0.2. The second peak in the critical current densityJc versusmagnetic field B curve shifts toward the high magnetic regime for the samplex = 0.2 compared withthat for the sample x = 0, but decreases to low magnetic field for the samplesx>0.2. Two superconducting transitions in resistivityρab indicate thatthe low Tc clusters,i.e. Gd1+yBa2−yCu3O7−δ solid solutions,are interspersed in the GdBa2Cu3O7−δ superconducting matrix. The δTc pinning resulting from the compositional fluctuations should be responsible for the enhancement ofJc and the trappedfield for the sample x = 0.2.