Enhanced flux pinning by combined atomic substitution and phase decomposition in cuprate superconductors

The use of combined atomic substitution and phase decomposition is shown to achieve substantial enhancement of flux pinning in Y–Ba-Cu–O ceramics. The substituent is chosen to provide a high density of nucleation sites for decomposition and at the same time enhancing Tc in the resulting composite superconductor. Bulk YBa2Cu4O8 (124) with 2.5% La substituted for Ba is decomposed by a short anneal beyond the stability boundary for YBa2Cu3O7 (123) at low oxygen pressure. The product, principally La-substituted 123 with stacking faults and precipitates of CuO in the grain boundaries, exhibits a 17-fold enhancement in intragrain Jc at 77 K and 0.75 Tesla over unprocessed 123, rising to 50-fold at 85 K. Magnetization Jc exceeds 104 A/cm2 at 0.75 Tesla for temperatures up to 87 K, the highest so far observed for a superconductor.