A novel gas-solid reaction process to synthesize low oxygen MgB ₂ powder using Mg vapour

We have established a novel reaction process using Mg vapour and B powder (a gas-solid reaction) to synthesize MgB ₂ 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 MgB ₂ 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 MgB ₂ is achieved at 3 h. At longer times such as 4 h, MgB ₂ decomposes to form MgB ₄ . It is deduced that the main reason for the unstable MgB ₂ 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 MgB ₂ , which can finally resolve the mystery of the effect of oxygen on superconductivity in this system.