Electron density and thermal effects in alpha quartz
Electron density and thermal effects in alpha quartz
复制标题
阿尔法石英中的电子密度和热效应
DOI：
10.1107/s0365110x62000845
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发表时间：
1962
期刊：
影响因子：
--
通讯作者：
B. Post
中科院分区：
文献类型：
--
作者：
R. A. Young;B. Post
A detailed analysis has been made of atomic positional coordinates and thermal motions in a-quartz. Complete data in three dimensions were obtained at room temperature using filtered Mo K radia-tion;(hie0) and (00/) reflections were also measured at 223 and 155 K. Intensities were measured with a scintillation counter. Fourier and least squares techniques were used to determine positional coordinates and the magnitude and orientation of atomic thermal ellipsoids. Data previously reported by Brill et al.(1939, 1942) have been refined by least squares methods and the new results have been found to be in good agreement with ours. The temperature dependence of the atomic coordinates and of the thermal parameters have been investigated by least squares analyses of data obtained at different temperatures and by direct comparison of electron density maps based on room and low temperature data. The applicability of the I) ebye approximation to the thermal data for a-quartz has also been investigated. Bond lengths at room temperature are: Si-O: 1.603±0.003 A and 1.611±0.002/~. The Si-O-Si angle is 143.9. Two of the four tetrahedral O-Si-O angles are close to 109; the others are 110.1. Introduction Alpha-quartz occurs with either of the enantiomorphi-cally related space groups, P312 or P322. There are three formula weights per unit cell. The cell dimen-sions, as given by Bradley & Jay (1933), are: a--4.9128+ _ 0.00005, c--5.4042+ _ 0.0001~. The positional parameters to be determined are, u, the distance from the threefold axis to the silicon atom, and the x, y, and z coordinates of one oxygen atom. Brill et al.(1939, 1942) investigated a-quartz by Fourier methods, using room temperature (hO. 1) data gathered with an ionization chamber. The crystal specimens were slabs of natural milk quartz. Detailed comparisons of our results with Brill's have been made, in part by refinement of their data, and will be discussed later.
