Pressure‐induced phase transition and pressure dependence of crystal structure in low (α) and Ca/Al‐doped cristobalite
Pressure‐induced phase transition and pressure dependence of crystal structure in low (α) and Ca/Al‐doped cristobalite
复制标题
低 (α) 和 Ca/Al 掺杂方英石中压力诱导的相变和晶体结构的压力依赖性
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
M. Saltzberg
中科院分区：
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作者：
J. Parise;A. Yeganeh;D. Weidner;J. Jorgensen;M. Saltzberg
研究了SiO2方石英和Ca/Al掺杂部分稳定的方石英（Cax/2 Si 2 − xAlxO 4）的相稳定性和原子水平压缩机制。用原位高压能量色散X射线衍射观察到的向较低对称相的相变发生在约1.2 GPa。低压相的结构模型通过对气体压力装置中粉末样品的中子粉末衍射数据进行Rietveld分析获得。这些数据是在高达0.6 GPa的压力和298和60 K下收集的。结果表明，在高压和低温下，刚性SiO 4四面体的旋转导致角连接框架的坍塌是两种材料致密化的主要机制。与相同压力和温度下的纯SiO2方石英相比，Ca/Al掺杂材料具有更大的晶胞体积。它还具有更大的Si-O-Si弯曲角和更扩展的框架，如由小的弯曲角和更大的弯曲角所证明的。
The phase stability and atomic‐level compression mechanisms for both SiO2 cristobalite, and for cristobalite partially stabilized by Ca/Al doping (Cax/2 Si2−xAlxO4), have been investigated. A phase transition to a lower symmetry phase, observed with in situ high‐pressure energy‐dispersive x‐ray diffraction, occurs at about 1.2 GPa. Structure models of the low‐pressure phase were obtained by Rietveld analysis of neutron powder‐diffraction data from powdered samples contained in a gas pressure apparatus. These data were collected at pressures up to 0.6 GPa and at 298 and 60 K. The results suggest collapse of the corner‐connected framework from rotations of the rigid SiO4 tetrahedra at high pressures and low temperatures as the dominant mechanism for the densification of both materials. Compared to pure SiO2 cristobalite at the same pressure and temperature, the Ca/Al‐doped material has a larger unit‐cell volume. It also has a larger Si‐O‐Si bending angle and a more expanded framework as evidenced by the sma...