Garnets in the majorite-pyrope system: symmetry, lattice microstrain, and order-disorder of cations
Garnets in the majorite-pyrope system: symmetry, lattice microstrain, and order-disorder of cations
复制标题
多数石榴石系统中的石榴石：对称性、晶格微应变和阳离子的有序无序
DOI：
10.1007/s00269-016-0852-3
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发表时间：
2017
影响因子：
1.4
通讯作者：
Kunimoto T. and Irifune T.
中科院分区：
文献类型：
--
作者：
Liu Z.;Du W.;Shinmei T.;Greaux S.;Zhou C. Arimoto T.;Kunimoto T. and Irifune T.
本文系统地研究了镁铝榴石-镁铝榴石体系中石榴石的相变、晶格微应变和阳离子的有序无序。利用Kawai型多面顶锤装置，在高温高压下合成了宝石级多晶石榴石。X射线衍射和拉曼散射研究表明，马来石相含量大于74摩尔分数的石榴石具有从立方结构到四方结构的明显相变。用X射线衍射谱上的Williamson-Hall图评价石榴石的微应变，表明石榴石的组成与其组成呈非线性关系。X射线衍射峰展宽的变化表明，这些石榴石的晶格微观应变可能与石榴石结构中不同阳离子通过耦合取代(Mg~(2+)+Si~(4+)=Al~(2+))取代所引起的局域结构不均有关。拉曼散射峰的宽度变化表明，中间组分的石榴石结构中存在阳离子无序。研究发现，中间石榴石和端员具有最小的微应变，而端员和中间成分之间的石榴石具有较大的微应变。
We present a systematic experimental study on the phase transition, lattice microstrain, and order–disorder of cations for garnets in the majorite–pyrope system. Polycrystalline gem-quality garnets were synthesized at high pressure and high temperature using a Kawai-type multi-anvil apparatus. A phase transition from a cubic to tetragonal structure is clearly observed for garnets with the majorite content of more than 74 mol % through X-ray diffraction (XRD) and Raman scattering studies. Microstrain of garnets, evaluated with the Williamson–Hall plot on XRD profiles, shows a nonlinear dependence of the garnet compositions. The variation of the XRD peak broadening suggests the lattice microstrain of these garnets may be associated with the local structural heterogeneities due to the substitution of different cations via the coupled substitution (Mg2++ Si4+= 2Al3+) in the garnet structure. The width variation of Raman scattering peaks indicates that cation disorder occurs in the garnet structure for intermediate compositions. It is found that intermediate garnets and end-members have a minimum of microstrain, while those between end-members and intermediate compositions possess a larger microstrain.