Silicon Monoxide at 1 atm and Elevated Pressures: Crystalline or Amorphous?
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- 作者：Khalid AlKaabi ; Dasari L. V. K. Prasad ; Peter Kroll ; N. W. Ashcroft ; Roald Hoffmann
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：March 5, 2014
- 年：2014
- 卷：136
- 期：9
- 页码：3410-3423
- 全文大小：746K
- 年卷期：v.136,no.9(March 5, 2014)
- ISSN：1520-5126
文摘
The absence of a crystalline SiO phase under ordinary conditions is an anomaly in the sequence of group 14 monoxides. We explore theoretically ordered ground-state and amorphous structures for SiO at P = 1 atm, and crystalline phases also at pressures up to 200 GPa. Several competitive ground-state P = 1 atm structures are found, perforce with Si鈥揝i bonds, and possessing Si鈥揙鈥揝i bridges similar to those in silica (SiO2) polymorphs. The most stable of these static structures is enthalpically just a little more stable than a calculated random bond model of amorphous SiO. In that model we find no segregation into regions of amorphous Si and amorphous SiO2. The P = 1 atm structures are all semiconducting. As the pressure is increased, intriguing new crystalline structures evolve, incorporating Si triangular nets or strips and stishovite-like regions. A heat of formation of crystalline SiO is computed; it is found to be the most negative of all the group 14 monoxides. Yet, given the stability of SiO2, the disproportionation 2SiO(s) 鈫?Si(s)+SiO2(s) is exothermic, falling right into the series of group 14 monoxides, and ranging from a highly negative 螖H of disproportionation for CO to highly positive for PbO. There is no major change in the heat of disproportionation with pressure, i.e., no range of stability of SiO with respect to SiO2. The high-pressure SiO phases are metallic.