Preparation and characterization of the new superconductor MgB2

Polycrystalline samples of the new superconductor MgB2 are prepared by a so lid-state reaction using Mg and B powders. The resistance measurement shows that the onset transition temperature and zero resistance transition tempe rature are T-c(onset) = 43.8 K and T-c0 = 37 K, respectively. The T-c0 stro ngly depends on measuring current. The diamagnetic transition temperature o f similar to 38 K is obtained by the ac susceptibility measurement. X-ray p owder diffraction spectra of MgB2 can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a = 0.30864 and c = 0.35212 nm. A second phase, probably MgO, is also found.