The crystal structure of agr;‐SiO2(low quartz) has been refined at 296, 78, and 13 K from time‐of‐flight neutron powder diffraction data. The major effect of temperature from 296 to 78 K is a nearly rigid body rotation of the SiO4tetrahedra. Below 78 K, tetrahedral rotation is substantially reduced giving rise to a much smaller thermal expansion. A comparison of the volume dependence of the Si‐O‐Si angle, the rotation angle for SiO4tetrahedra and thec/aratio suggests that the mechanism for expansion may be changing from tetrahedral rotation to tetrahedral distortion at the lowest temperatures. The inverse linear relation between the mean Si‐O bond distance and −sec(Si‐O‐Si) which has been observed for silica minerals at both ambient and high‐temperature conditions appears to be consistent with the structural variations that occur at low temperatures.
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机译：在296、78和13 K处，从飞行中子粉末衍射数据中，对SiO2（低石英）的晶体结构进行了细化。温度从 296 K 到 78 K 的主要影响是 SiO4 四面体的近乎刚体旋转。低于 78 K，四面体旋转显着减少，从而产生更小的热膨胀。比较Si‐O‐Si角的体积依赖性，SiO4四面体的旋转角度和c/aratio表明，在最低温度下，膨胀机制可能从四面体旋转转变为四面体畸变。在环境和高温条件下观察到的二氧化硅矿物的平均Si‐O键距离与−sec（Si‐O‐Si）之间的反线性关系似乎与低温下发生的结构变化一致。
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