Abstract
We have developed an electrostatic levitation furnace for performing a containerless solidification process on superconductors. Spherical niobium is solidified from the large undercooled state at approximately around 400°C below the melting temperature. The morphologies show homogeneous cellular structures over the entire surface. X-ray Laue photographs indicate that the spherical niobium is composed of a single grain. Magnetization below the superconducting transition temperature shows perfect diamagnetism in the low magnetic field independent of whether loading is carried out under field cooling or zero-field cooling conditions. The field dependence of magnetization shows almost reversible behavior as that of an ideal type II superconductor. These results suggest that the spherical niobium formed from the large undercooled state in this study has a very small number of flux-pinning centers compared to that formed by conventional arc melting.
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