Crystal chemical studies on incommensurately modulated mullite

莫来石的晶体结构（2.1莫来石，即2Al2O3）。SiO2, Al4.8Si1.2O9.6， Z=1)的特征是由共享边的AlO6八面体链和受桥接氧位空位影响的（Al,Si）O4四面体双链连接而成。Angel et al. 1991（美国）。矿物学报，76,332-342)研究了莫来石的非相应调制结构，得出了阳离子和氧空位部分有序的结论。然而，他们使用了质量较低的莫来石单晶进行研究，因此无法提供充分了解莫来石真实结构所需的信息。本研究的目的是通过基于Bragg中子衍射数据和超结构反射的高维空间晶体结构分析来进一步了解。一种清晰无夹杂的czochralski生长莫来石单晶可用于此目的。实验工作将伴随着氧空位模型计算。这些有序模式的发现将与晶格参数和莫来石的弹性和热膨胀性质有关。

The crystal structure of mullite (2:1-mullite, i.e. 2Al2O3 . SiO2, Al4.8Si1.2O9.6, Z=1) is characterized by chains of edge-sharing AlO6 octahedra linked by double chains of (Al,Si)O4 tetrahedra affected by vacancies on the bridging oxygen position. Angel et al. 1991 (Amer. Mineral. 76, 332-342) studied the incommensurately modulated structure with the conclusion that the cations and oxygen vacancies are partially ordered in mullite. However, they used a mullite single crystal of low quality for their studies, and thus were not able to provide the information required to fully understand the real structure of mullite. It is the aim of this study to gain further understanding by crystal structure analysis in higher dimensional space based on neutron diffraction data of Bragg and super-structure reflections. A clear inclusion-free Czochralski-grown mullite single crystal is available for that purpose. The experimental works will be accompanied by oxygen vacancy modeling calculations. The findings of the ordering patterns will be correlated with the lattice parameters and properties of mullite like elasticity and thermal expansion.