Phase relations of the Al₂O₃–SiO₂ system were determined by multi-anvil experiments at pressures of 13–21 GPa and temperatures of 2300–2800 K. We obtained a new high-pressure Al₂Si₂O₇ phase (227-phase), which possesses a triclinic unit cell (Z = 3) with a = 7.0237(12) Å, b = 7.1002(14) Å, c = 6.6729(10) Å, α = 103.466(15)°, β = 99.107(15)°, γ = 60.542(12)°, and V = 281.41(24) ų, in addition to the two new high-pressure Al₂SiO₅ phases reported recently, kyanite II and kyanite III. Because of the formation of the three new phases at temperatures above 2400 K, the phase relations are complicated, in contrast to the previously-known phase assemblage of corundum + stishovite stable at the post-kyanite pressures and temperatures below 2400 K. The three new phases and also kyanite are chemically invariant intermediate phases in the binary system and can be formed by the isothermal reactions, Al₂O₃ (corundum) + SiO₂ (stishovite) = Al₂SiO₅ (kyanite II or III) and Al₂SiO₅ (kyanite, II, or III) + SiO₂ (stishovite) = Al₂Si₂O₇ (227-phase). In comparison to kyanite II and kyanite III, 227-phase is formed at higher temperatures. Crystal structure of 227-phase is based on distorted closest packing of O²⁻ and tetrahedrally- and octahedrally-coordinated cations, similar to those of kyanite and kyanite II. The appearance of 227-phase once again suggests the key effect of temperature for stabilizing dense crystal structures fully made of Al–O and Si–O polyhedra at high pressures.

Al ₂ O ₃ -SiO ₂体系的相关系是通过多砧实验在 13-21 GPa 的压力和 2300-2800 K 的温度下确定的。我们获得了一种新的高压 Al ₂ Si ₂ O ₇相（227相），它拥有一个三斜晶胞（Z  = 3），a  = 7.0237(12) Å, b  = 7.1002(14) Å, c  = 6.6729(10) Å, α  = 103.466(15)°, β  = 99.107(15)°, γ  = 60.542(12)°, V  = 281.41(24) Å ³，此外还有两个新的高压 Al ₂ SiO最近报道了_{5 个}阶段，蓝晶石 II 和蓝晶石 III。由于在高于 2400 K 的温度下形成了三个新相，因此相关系很复杂，这与先前已知的在蓝晶石后压力和低于 2400 K 温度下稳定的刚玉 + stishovite 相组合形成对比。这三个新相相和蓝晶石是二元体系中化学不变的中间相，可以通过等温反应形成，Al ₂ O ₃ (刚玉) + SiO ₂ (stishovite) = Al ₂ SiO ₅ (蓝晶石 II 或 III) 和 Al ₂ SiO ₅ (蓝晶石、II 或 III) + SiO ₂ (stishovite) = Al ₂ Si₂ O ₇ (227相)。与蓝晶石 II 和蓝晶石 III 相比，227 相在更高的温度下形成。227 相的晶体结构基于 O ^2-和四面体和八面体配位阳离子的扭曲最密堆积，类似于蓝晶石和蓝晶石 II。227 相的出现再次表明温度对在高压下稳定完全由 Al-O 和 Si-O 多面体构成的致密晶体结构的关键作用。