晶体孪晶
结晶学
四面体
材料科学
晶体结构
声子
从头算
分子物理学
物理
凝聚态物理
化学
量子力学
微观结构
作者
Vratislav Langer,Ľ. Smrčok,Daniel Tunega,Gernot Wirnsberger
出处
期刊:Acta crystallographica
[International Union of Crystallography]
日期:2005-11-14
卷期号:61 (6): 627-634
被引量:10
标识
DOI:10.1107/s0108768105026698
摘要
The structure of deca-dodecasil 3R (DD-3R), Si120O240, a very well suited material for the synthesis of inorganic/organic composites structured on a nanometer level, has been investigated in detail. So far, a highly complicated twinning has hampered its structure description at a desirable level of accuracy. This twinning has now been resolved and a new structure determination is presented. Structure refinement in the R\bar 3 space group revealed a large, unusually shaped atomic displacement ellipsoid for oxygen-bridging units (tetrahedra), bridging Si-O bonds shorter than expected and the linear Si-O-Si' bond angle dictated by special positions at a threefold axis. A structure model based on a statistically disordered bridging O atom improved the accuracy of the Si-O bonds of interest, but provided unacceptable O-O contacts. To solve this dilemma, ab initio NVT molecular dynamics calculations were performed to study the possible configurations. Wavelet analysis of the time variations of selected Si-O distances pointed to a synchronous shift of the whole building units (tetrahedra). Low-frequency features of the calculated phonon density of states agree well with the published INS (inelastic neutron scattering) spectra of several silica polymorphs, indicating that the nature of the disorder in DD-3R is dynamic rather than static.
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