Low temperature synthesis of MgB ₂

We report the synthesis of MgB ₂ with bulk superconducting properties by conventional solid state methods at temperatures as low as 550°C. Mg deficiencies of the type Mg _1-xB ₂ were tested. T _c was found to decrease by about 1 K at large x, though the amount of nonstoichiometry, if any, is likely to be very small. For specific processing conditions, indications of the 25-30 K transition often seen in thin films were seen in the bulk materials. The lower temperature transition may be associated with the grain boundaries. These results indicate that it should be possible to fabricate MgB ₂ with bulk properties in in situ thin films at temperatures of 600°C or less.