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.