Amorphous Magnesium Silicide

Abstract

A first principles molecular dynamics technique is employed to generate an amorphous magnesium silicide (Mg2Si) model from its liquid state and its structural, electrical and mechanical features are disclosed for the first time. Si atoms form predominantly the standard square dodecahedron-like and the tri-capped trigonal prism-like configurations while Mg atoms arrange themselves primarily in higher coordinated crystal-like and icosahedrallike polyhedrons. The mean coordination number of Mg and Si is estimated to be similar to 12.84 and similar to 8.2, respectively. Si-Si homopolar bonds are also presented in the amorphous network, in contrast to the crystal. Based on our findings, we propose that the amorphous model has a short-range order, quite different than that of the anti fluorite Mg2Si crystal but similar to that of metallic glasses. The different local structure of the amorphous state yields distinct electronic and mechanical properties, relative to the crystal. Within the known limitation of DFT-GGA simulations, the amorphous Mg2Si is found to be semimetal though the anti-fluorite structure is semiconductor. Furthermore, amorphous Mg2Si is predicted to be less brittle than the crystal structure. Since the potential use of the Mg2Si crystal as a biodegradable implant material is hindered because of its brittle behavior, here we propose that amorphous or nanoglass forms might eliminate this limitation of Mg2Si and hence it can serve as an implant material in near future.