The influence of CeO2 addition on microstructure and superconducting properties of GdBCO-Ag single grain bulk superconductors

Abstract Bulk single-grain GdBCO superconductors (nominal composition 1 mol GdBa2Cu3O7-δ + ½ mol Gd2BaCuO5 + 20 wt% Ag2O + Z wt% CeO2 (Z = 0.4, 1.0, 1.6) grown using the top-seeded melt-grow process are studied by differential thermal analysis, X-ray diffraction, scanning electron microscopy and magnetic measurement of local superconducting properties. The amount of CeO2 added is shown to have a significant effect on thermal behaviour, phase composition, microstructure and local superconducting properties. The observed behaviour is explained by the dissolution of Ce in the melt L' formed by monotectic melting of the samples. Ce dissolved in melt L' reduces the substitution of Ba by Gd in the Gd123 crystal lattice. This effect causes an increase in the superconducting transition temperature Tc with added CeO2, an increase in Tc with distance from the seed and influences the critical current density by chemical pinning. The obtained results open a new effective way to improve the superconducting properties of LREBCO bulk single-grain superconductors grown in air.