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). While both structures contain Mg@As4 tetrahedra, Mg3Si6As8 is also comprised of Mg@As6 octahedra. 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.

Structural and optical properties of two new non-centrosymmetric compounds: MgSiAs2 and Mg3Si6As8

255th National Meeting (2018)

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