New insights into the high-pressure polymorphism of SiO2 cristobalite
New insights into the high-pressure polymorphism of SiO2 cristobalite
复制标题
DOI：
10.1007/s00269-011-0424-5
复制
发表时间：
2011-07-01
影响因子：
1.4
通讯作者：
Downs, Robert T.
中科院分区：
文献类型：
--
作者：
Dera, Przemyslaw;Lazarz, John D.;Downs, Robert T.
SiO2 α-方石英的单晶X射线衍射实验表明，众所周知的可逆位移相变方石英-II，发生在约1.8 GPa，可以抑制快速压力增加，导致过压亚稳态，持续高达10 GPa的压力。在另一个缓慢的压力增加实验中，观察到单斜高压第二相在类似于1.8 GPa的压力下形成，与早期的原位研究一致，并且其晶体结构已经明确确定。单晶数据已被用来完善的结构模型的两个阶段的压力范围内的形成方石英X-I在类似于12 GPa的阈值，提供重要的约束的可行性的两个竞争的二氧化硅致密化模型在文献中提出的，基于量子力学计算。方石英X-I获得的初步衍射数据揭示了一个单斜晶胞，与目前假设的模型相矛盾。
Single-crystal X-ray diffraction experiments with SiO2 alpha-cristobalite reveal that the well-known reversible displacive phase transition to cristobalite-II, which occurs at approximately 1.8 GPa, can be suppressed by rapid pressure increase, leading to an overpressurized metastable state, persisting to pressure as high as 10 GPa. In another, slow pressure increase experiment, the monoclinic high-pressure phase-II was observed to form at similar to 1.8 GPa, in agreement with earlier in situ studies, and its crystal structure has been unambiguously determined. Single-crystal data have been used to refine the structure models of both phases over the range of pressure up to the threshold of formation of cristobalite X-I at similar to 12 GPa, providing important constraints on the feasibility of the two competing silica densification models proposed in the literature, based on quantum mechanical calculations. Preliminary diffraction data obtained for cristobalite X-I reveal a monoclinic unit cell that contradicts the currently assumed model.