NaSi and Si clathrate prepared on Si substrate

Abstract

In this study, we attempted to prepare films of Si clathrates (Na8Si46 (Type I) and Nax Si136(Type II)) and NaSi by using Si single crystalline substrates as the Si source. NaSi, which is the precursor of the Si clathrate, was successfully generated as a highly orientated film on the Si substrate, by exposing Na vapor under Ar atmosphere. The NaSi film was then transformed into Si clathrate film of several µm in thickness, by heat treatment (400 °C, 3 h) under vacuum (∼ 10‐4 Pa). Type I and II clathrates were selectively synthesized by using the crystal orientation (100) and (111) of Si substrates, respectively. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Group IV clathrates: synthesis, optoelectonic properties, and photovoltaic applications

“…Thermal decomposition of thin film Zintl precursors A few reports on synthesis of type II clathrates in thin film form exist. 22,48,49,53 In all cases, a thin film of Zintl precursor (NaSi) is formed by reacting Na metal with Si. The source of Si can be a Si wafer or a thin film of Si on a substrate and precursor synthesis can either be carried out under Ar or vacuum.…”

“…Kume et al has reported growth of type I clathrate (Na 8 Si 136 ) using this technique on a (100) Si wafer. 48 However, when a (111) oriented Si wafer was used, type II clathrate was synthesized. Since phase selection in Si clathrate on thermal decomposition of Zintl phase is very sensitive to the local environment (Na vapor pressure, temperature, etc.…”

“…So far, the techniques employed to grow (type I or type II) clathrate thin films are: (a) Pulsed laser deposition (PLD), (b) thermal decomposition of a thin film Zintl precursor phase and more recently, (c) melt spinning thick films of clathrate on a substrate. 22,[47][48][49][50] Of these, both the PLD and melt spinning techniques have been demonstrated only for type I clathrates. Both these techniques require clathrate powder for making the target (PLD) or the melt (melt spinning).…”

In Operando Mechanism Analysis on Nanocrystalline Silicon Anode Material for Reversible and Ultrafast Sodium Storage

“…Compared with the commercial carbon‐based anodes with a relatively low theoretical capacity (below 380 mAh g −1 ) in LIBs, silicon (Si)‐based materials are particularly promising because of their extremely high reversible specific capacity (3590 mAh g −1 , corresponding to Li 15 Si 4 ) . Very excitingly, many previous theoretical calculations have predicted that Na can also alloy with Si to form NaSi (Si + Na + + e − ↔ NaSi), providing a specific capacity around 960 mAh g −1 . Therefore, from the viewpoint of high energy density, Si‐based anode material is also an excellent choice for SIBs.…”

Advanced Nanostructured Anode Materials for Sodium‐Ion Batteries

“…Silicon is the promising anode material of LIBs for its extremely high reversible capacity . Theoretical calculations show that Na can also react with Si to form NaSi with a capacity of 960 mAh g −1 . But the low conductivity and large volume change make this kind of anode materials have low capacity and cycle performance .…”