Influence of Bi, Se and Te additions on the formation temperature of MgB₂

The formation of the MgB2 superconducting compound from a mixture of Mg and amorphous B powders with various low melting point metals (Bi, Se and Te) was studied in situ by means of high-energy (synchrotron) x-ray diffraction in wires with a composite Cu/Nb sheath. In comparison with an undoped sample, it was found that the addition of Bi results in a clear lowering of the formation temperature of MgB2, whereas Se and Te have no significant influence. Tc is slightly higher in the Bi-doped sample than in the others but the jc in this case is lower than in the pure MgB2 sample, probably due to the presence of remaining Mg3Bi2 particles that formed as an intermediate compound during reaction. Likewise, in the Se-and Te-doped samples, MgSe and MgTe respectively form below 450 °C. Whereas jc is also depressed in the Se-doped sample, the MgTe particles do not appear to affect the performance of the Te-doped wire.