Preparation and Characterization of the New SuperconductorMgB₂

Polycrystalline samples of the new superconductor MgB₂ are prepared by solid state reaction using Mg and B powders. The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are T^onset_c = 43.8 K and T_c0 = 37 K, respectively. The T_c0 depends on measuring current strongly. The diamagnetic transition temperature of ～38 K is obtained by the ac susceptibility measurement. X-ray powder 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.