The ability of silicon to bond with itself underlies the possibility for a breadth of metastable allotropes with novel properties. Two such allotropes are type I and type II Si clathrates, materials which are characterized by their formation around guest species (typically partially ionized Na) and their resultant cage structures. These clathrates act as metals when the cages are completely filled with Na, yet upon liberation of the guest species they become wide band gap semiconductors. Using molecular dynamic (MD) simulations, the nucleation and growth of these clathrates are probed. An order parameter for the visualization and quantification of order in Si clathrates is presented and evaluated under variable temperature and guest concentration, comprising 30 unique systems and 6000 ns of simulation time. Systems run at 700 K with Na guest concentrations between 50 and 100 percent show the most reordering from an amorphous phase. Elucidating growth phenomena from a computational standpoint synergistically guides experimental synthesis of these materials, which show promise in a range of future applications.

Allegory of the cage: Shedding light on order in silicon clathrates

255th National Meeting (2018)

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