Solubility and superconductivity of Gd_1+xBa_2-xCu ₃O_7-δ compounds (x = -0.1,0,0.05,0.1,0.15 and 0.2)

The RE/Ba substitution has a significant effect on the growth, microstructure and flux pinning properties of melt-processed Gd _1+xBa_2-xCu₃O_7-δ, superconductors. We prepared a series of Gd_1+xBa_2-xCu ₃O_7-δ, (Gd123 solid solutions) with x = -0.1,0,0.05,0.1,0.15 and 0.2. The single phase of Gd123 solid solutions was confirmed with both X-ray diffraction and DTA analysis for x - 0 to 0.1 as-grown samples, quenched in air. DTA/TG analysis in air showed that the thermal stability decreases with increasing x. After the post-annealing in flowing argon gas at 940°C for 10 h (ArPA), the Gd123 solid solutions with x - 0.1,0.15 and 0.2 were decomposed into Gd₂BaCuO₅ and Gd123 solid solutions with low substitution levels and minor liquid phases. The critical transition temperatures (TVs) of Gd123 solid solutions with the ArPA show dramatical increase compared to the samples without ArPA. The Gd123 solid solutions annealed in O₂ at 400°C show a narrower superconducting transition width than those treated at 350°C. These results contribute to improve the properties of the melt-processed bulk superconductors.