Pakhomova Anna, Bykova Elena, Bykov Maxim, Glazyrin Konstantin, Gasharova Biliana, Liermann Hanns-Peter, Mezouar Mohamed, Gorelova Liudmila, Krivovichev Sergey, Dubrovinsky Leonid
Deutsches Elektronen-Synchrotron (DESY), Hamburg 22607, Germany.
Bayerisches Geoinstitut, University of Bayreuth, Bayreuth 95440, Germany.
IUCrJ. 2017 Aug 10;4(Pt 5):671-677. doi: 10.1107/S2052252517010612. eCollection 2017 Sep 1.
Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four- to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaBSiO, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the SiO groups of danburite first transform into chains of vertice-sharing SiO trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO octahedra (danburite-III). It is suggested that the unusual formation of an SiO configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.
由于其在技术和地质方面的高度相关性，硅酸盐是研究最多的无机化合物类别之一。在环境条件下，硅酸盐中的硅几乎完全由四个氧原子配位，而高压处理通常会导致配位数从四倍增加到六倍。本文报道了对赛黄晶（CaBSiO）的高压单晶X射线衍射研究，这是第一种显示硅配位通过三角双锥从四面体逐步转变为八面体的化合物。在压缩过程中，赛黄晶的SiO基团首先转变为顶点共享的SiO三角双锥链（赛黄晶-II），随后转变为边共享的SiO八面体链（赛黄晶-III）。有人认为，SiO构型的异常形成是填充赛黄晶-II扭曲六方密堆积中五配位空隙的结果。
