Rapid, energy-efficient and pseudomorphic microwave-induced-metal-plasma (MIMP) synthesis of Mg2Si and Mg2Ge

Abstract

Polycrystalline magnesium silicide, Mg₂Si and magnesium germanide, Mg₂Ge were synthesised from the elemental powders via the microwave-induced-metal-plasma (MIMP) approach at 200 W within 1 min in vacuo for the first time. The formation of reactive Mg plasma facilitated by the high-frequency electromagnetic field (2.45 GHz) is at the origin of the ultrafast reaction kinetics in these preparations. Powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) attest to the high purity of the products. Both SEM and Transmission Electron Microscopy (with Selected Area Electron Diffraction) (TEM/SAED) demonstrate the pseudomophic nature of the metal plasma reactions such that use of nanoporous Ge starting material leads to the production of nanoporous germanide, Mg₂Ge. Covalent Mg–Si and Mg–Ge bonds with partial ionic character are suggested by XPS, while the refined crystal structures are consistent with Mg–Mg interactions within the cubane-like clusters in Mg₂X antifluorite unit cells. The MIMP method unlocks not only the sustainable synthesis of Mg₂X materials but also the wider production of intermetallics and Zintl phases of prescribed morphology.