A novel gas–solid reaction process to synthesize low oxygen MgB2 powder using Mg vapour

We have established a novel reaction process using Mg vapour and B powder (a gas–solid reaction) to synthesize MgB2 powder with a low oxygen content. For the first time, we tried to eliminate the oxygen in Mg powder with a specially designed furnace tube that can keep the sample under an inert atmosphere throughout the entire synthesis process. The duration of heat treatment has a conspicuous effect on the phase formation of MgB2 which differs greatly from the conventional solid state reaction method. At short durations such as 1 h, unreacted B powder is ubiquitous in the sample. Full formation of MgB2 is achieved at 3 h. At longer times such as 4 h, MgB2 decomposes to form MgB4. It is deduced that the main reason for the unstable MgB2 phase formation in the gas–solid reaction is the Mg vapour present during the entire process. A feasible chemical reaction model of the novel gas–solid reaction has been established. This work provides an important foundation to obtain almost oxygen-free MgB2, which can finally resolve the mystery of the effect of oxygen on superconductivity in this system.