Twinning in tetragonal leucite
Twinning in tetragonal leucite
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四方白榴石中的孪晶
DOI：
10.1007/bf00220699
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发表时间：
1988
影响因子：
1.4
通讯作者：
E. Salje
中科院分区：
文献类型：
--
作者：
D. Palmer;A. Putnis;E. Salje
天然白钨矿KAlSi 2 O 6从立方对称性到四方对称性的变化涉及两种类型的孪生，它们随着温度的降低而顺序出现：（1）片层，与点群对称性减少m3 m至4/mmm相关;（2）部分面体，与4/mmm至4/m的变化相关。从X射线旋进照片和TEM衍射图和图像中推断出了孪晶取向。利用自发应变的概念和相邻畴间的对称关系，理论上证实了这一点。层状孪晶具有平行于立方相的{101}的边界，并且被半面体孪晶横切，半面体孪晶具有不规则的边界，其中相邻畴中的x和y互换。在电子显微镜的尺度上，从孪生交叉所产生的扭曲揭示了一个弯曲的孪生壁相邻的另一个，并通过针形域。片层孪晶的宏观取向与晶格参数有关，因此与自发应变的大小有关。这反过来又导致了m3 m到4/mmm变换的序参数的表征。
The change from cubic to tetragonal symmetry in natural leucite, KAlSi2O6, involves two types of twinning, which appear sequentially with decreasing temperature: (1) lamellar, associated with the point group symmetry reduction m3m to 4/mmm; (2) merohedric, associated with the change 4/mmm to 4/m. Twin orientations have been deduced from X-ray precession photos and TEM diffraction patterns and images. These are confirmed by theory, using the concept of spontaneous strain and the symmetry relations between adjacent domains. Lamellar twins have boundaries parallel to {101} of the cubic phase, and are cross-cut by the merohedric twins, which have irregular boundaries with x and y in adjacent domains interchanged. On an electron microscopic scale, the distortion arising from twin intersections is revealed by a curvature of one twin wall adjacent to another, and by needle-shaped domains. The macroscopic orientation of the lamellar twins is related to the lattice parameters and hence the magnitude of the spontaneous strain. This in turn leads to the characterisation of the order parameter for the m3m to 4/mmm transformation.