The crystal structure of adamantane: an example of a false minimum in least squares
The crystal structure of adamantane: an example of a false minimum in least squares
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金刚烷的晶体结构：最小二乘法中错误最小值的示例
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发表时间：
1967
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通讯作者：
S. H. Goodman
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作者：
J. Donohue;S. H. Goodman
Steinberger, 1966）因此尚未确定。将已发表的 ZnS 多型体层序列与 SiC 中已知的层序列进行比较，立即表明，ZnS 多型体的 Zhdanov 符号中的元素数量通常小于 SiC 多型体中报道的元素数量。即，ZnS多型体的六方晶比例有降低的倾向。对于 SiC 多型体，解释大多数观察到的多型体生长的理论是 Frank (1961) 和 Mitchell (1957) 的理论，并经 Krishna & Verma (1965) 修改。该理论基于这样的事实：SiC 中首先形成具有 (00.1) 面的薄板。薄片可以具有结构4L、6L或15L之一（这些是最常见的SiC结构）。由于屈曲，会出现台阶。其高度通常小于基本结构晶胞的c尺寸。由此形成螺旋位错，确保进一步生长；该位错的 Burgers 矢量是基本 c 平移的非整数倍。对于 ZnS 中的多型性，上述模型目前的形式不太可能是正确的。首先，在生长的初始阶段，细针形成轴[00.1]；这种针不能按照针对血小板所建议的方式弯曲。其次，在观察到的 ZnS 多型中，有一些在其 Zhdanov 序列中具有大元素 [例如(17 4 2 3)]，而根据 Mitchell-Verma 模型，不可能预期如此大的元素。因此，需要对上述模型进行修改，或者完全不同的模型来解释 ZnS 的多型性。然而，考虑这样一个模型似乎还为时过早，因为已知的 ZnS 多型体数量仍然太少，无法对实验与理论进行有意义的比较。
Steinberger, 1966) have for this reason not yet been determined. Comparison of published ZnS polytype layer sequences with those known in SiC immediately demonstrates the fact that the numbers of elements in the Zhdanov symbols of ZnS polytypes are, in general, smaller than those reported in SiC polytypes. In other words, the percentage of hexagonality of ZnS polytypes tends to be lower. For SiC polytypes, the theory which explains the growth of most observed polytypes is that of Frank (1961) and Mitchell (1957), as modified by Krishna & Verma (1965). This theory is based on the fact that in SiC a thin platelet with (00.1) faces is at first formed. The platelet may have one of the structures 4L, 6L or 15L (these being the most frequent SiC structures). As a result of buckling, a step appears. Its height is usually less than the c dimension of the unit cell of the basic structure. A screw dislocation is thus formed which ensures further growth; the Burgers vector of this dislocation is a non-integral multiple of the basic c translation. It is very unlikely that for polytypism in ZnS the above model is correct in its present form. First, in the initial stages of the growth thin needles form with the axis [00.1]; such needles cannot buckle in the way proposed for platelets. Secondly, among the observed ZnS polytypes there are some which have large elements in their Zhdanov sequence [e.g. (17 4 2 3)], whereas on the basis of the Mitchell-Verma model such large elements can not be expected. A modification of the above model, or else a quite different one is, therefore, needed for the explanation of polytypism in ZnS. It seems to be, however, premature to contemplate such a model, since the number of known ZnS polytypes is still too low for meaningful comparison of experiment with theory.