Inhomogeneity of SmBCO bulk superconductors grown in air

The local superconducting properties and microstructure of SmBCO bulk single-grain superconductors with the addition of different quantities of BaO₂ were studied. The single-grain bulk SmBCO superconductors were fabricated via the top-seeded melt growth process in air. Increasing transition temperature, critical current density and the narrowing superconducting transition width were observed with BaO₂ addition. It was shown that the transition temperature and critical current density depend on the distance from the seed. Microstructural analysis showed that the reaction of Ba with the supporting ZrO₂ bars is responsible for the gradient of Ba concentration in the peritectic melt, and consequent changes in Sm/Ba substitution in the Sm123 crystal lattice lead to the inhomogeneity of local superconducting properties. (paper)