Formation of inclusion type silicon phases induced by inert gases

Silicon clathrate, an important allotrope of silicon, has attractive opto-electronic properties for energy applications. However, it remains an experimental challenge to synthesize electrically undoped, intrinsic clathrate. Here we show, through high-throughput computer modeling, that unconventional silicon phases spontaneously nucleate from liquid silicon in the presence of noble gases under high pressure and high temperature. In particular, our results show that a medium-sized noble gas, for example, argon, can trigger the nucleation and growth of inert-gas silicon clathrate, whereas a small noble gas such as helium is able to induce the formation of an unconventional, inclusion-type compound Si2He. The formation of both silicon phases can be attributed to the same thermodynamic and kinetic rationale that explains the crystallization of clathrate hydrate, an isostructural analog. Our findings, along with the gained molecular insights, thus strongly suggest a viable experimental synthesis route for these silicon phases using noble gases at high pressure.