Silica (${\mathrm{SiO}}_2$), as a raw material of silicon, glass, ceramics, abrasive, and refractory substances, etc., is of significant importance in industrial applications and fundamental research such as electronics and planetary science. Here, using a crystal structure searching method and first-principles calculations, we predicted that a ground state crystalline phase of silica with $R\overline{3}$ symmetry is stable at around 645–890 GPa, which contains six-, eight-, and nine-coordinated silicon atoms and results in an average coordination number of eight. This mixed-coordination silica fills in the density, electronic band gap, and coordination number gaps between the previously known sixfold pyrite-type and ninefold ${\mathrm{Fe}}_2\mathrm{P}$-type phases, and may appear in the core or mantle of super-Earth exoplanets, or even the solar giant planets such as the Neptune. In addition, we also found that some silicon superoxides, Cmcm ${\mathrm{SiO}}_3$ and Ccce ${\mathrm{SiO}}_6$, are stable in this pressure range and may appear in an oxygen-rich environment. Our finding enriches the high-pressure phase diagram of silicon oxides and improves understanding of the interior structure of giant planets in our solar system.

中文翻译：

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兆帕压力下的混合配位二氧化硅

二氧化硅（${\mathrm{二氧化硅}}_2$）作为硅，玻璃，陶瓷，磨料和难熔物质等的原材料，在工业应用和基础研究（例如电子学和行星科学）中具有重要意义。在这里，使用晶体结构搜索方法和第一性原理计算，我们预测了二氧化硅的基态晶相具有$\mathrm{[R}\overline{3}$对称性稳定在645-890 GPa左右，其中包含六，八和九配位的硅原子，平均配位数为8。这种混合配位二氧化硅填补了先前已知的六倍黄铁矿型和九倍黄铁矿型之间的密度，电子带隙和配位数间隙。${铁}_2\mathrm{P}$型相，并可能出现在超地球系外行星的核心或地幔中，甚至出现在海王星等太阳巨行星上。此外，我们还发现了一些超氧化硅，Cmcm ${\mathrm{二氧化硅}}_3$和Ccce ${\mathrm{二氧化硅}}_6$，在这个压力范围内是稳定的，并且可能出现在富氧环境中。我们的发现丰富了氧化硅的高压相图，并增进了对我们太阳系中巨型行星内部结构的理解。