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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Monoclinic and hexagonal nepheline structures of (Na3/4K1/4)AlGeO4
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Monoclinic and hexagonal nepheline structures of (Na3/4K1/4)AlGeO4

机译：（Na3 / 4K1 / 4）AlGeO4的单斜和六角形霞石结构

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摘要

Hexagonal (Na3/4K1/4)AlGeO4 crystallizes in the space group P6(3) with unit-cell parameters a = 10.164 (2), c = 8.540 (2) Angstrom and Z = 8 [wR(F-2) = 0.066 for all 3060 independent reflections]. Monoclinic (Na3/4K1/4)AlGeO4 crystallizes in the space group P2(1) with unit-cell parameters a = 10.0477 (4), b = 8.5764 (4), c = 10.2118 (4) Angstrom, beta = 119.035(1)degrees and Z = 8 [wR(F-2) = 0.120 for all 3194 independent reflections measured on a twinned crystal]. Both structures belong to the large family of stuffed tridymites, with the Al and Ge atoms occupying tetrahedral sites, and the alkali atoms occupying the cavities of the tetrahedral framework. Hexagonal (Na3/4K1/4)AlGeO4 is isostructural with the silicate mineral nepheline (Na3/4K1/4)AlSiO4, while monoclinic (Na3/4K1/4)AlGeO4 corresponds to a minor distortion of the nepheline structure. Chemical analysis by electron microprobe and structure determination of flux-grown single crystals indicate that the hexagonal form with the chemical formula (Na0.78K0.19)Al0.97Ge1.03O4 may be stabilized by an alkali deficiency similar to that found in hexagonal natural nephelines. In contrast, all alkali sites are fully occupied in the monoclinic form of composition (Na0.75K0.25)AlGeO4 and the lower symmetry eliminates the oxygen disorder present in the hexagonal form. [References: 15]
机译：六角形（Na3 / 4K1 / 4）AlGeO4在空间单元P6（3）中结晶，其晶胞参数为a = 10.164（2），c = 8.540（2）埃和Z = 8 [wR（F-2）= 0.066所有3060个独立反射]。单斜晶（Na3 / 4K1 / 4）AlGeO4在单元格参数为a = 10.0477（4），b = 8.5764（4），c = 10.2118（4）埃，β= 119.035（1）的空间群P2（1）中结晶度和Z = 8 [对于在孪晶上测量的所有3194个独立反射，wr（F-2）= 0.120]。这两个结构都属于填充三体的大家族，其中Al和Ge原子占据了四面体位置，而碱原子占据了四面体骨架的空腔。六角形（Na3 / 4K1 / 4）AlGeO4与硅酸盐矿物霞石（Na3 / 4K1 / 4）AlSiO4等结构，而单斜晶（Na3 / 4K1 / 4）AlGeO4对应于霞石结构的较小变形。电子探针的化学分析和助熔剂生长的单晶的结构确定表明，具有化学式（Na0.78K0.19）Al0.97Ge1.03O4的六方形式可以通过类似于六方天然霞石中发现的碱缺乏来稳定。 。相反，所有碱位都完全以单斜晶形式的组成（Na0.75K0.25）AlGeO4占据，较低的对称性消除了六角形形式的氧紊乱。 [参考：15]

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