3, University of California, Davis, Davis, California, United States
2, Jet Propulsion Laboratory, Pasadena, California, United States
Two compounds in the Mg-Si-As system have been synthesized using solid state methods and structurally characterized. MgSiAs2 has been reported theoretically multiple times as a part of the well-known II-IV-V2 family, but has never been successfully synthesized until now. Similar to other II-IV-V2 compounds, it crystallizes with a chalcopyrite structure in the space group I-42d (No. 122). Mg3Si6As8 is a cubic compound with a new structure type that crystallizes in the space group P4332 (No. 207). Both compounds crystallize in chiral space groups though only MgSiAs2 is expected to exhibit non-linear optical activity. Mg3Si6As8 belongs to the single non-centrosymmetric crystal class that falls outside of the group of non-linear optically active compounds. According to band structure calculations, both compounds possess pseudo-direct band gaps of 1.03 eV for MgSiAs2 and 1.55 eV for Mg3Si6As8. The additional property of high chemical resistance to oxidizers and acids make them contenders for optoelectronic materials.