Crystal chemical studies on incommensurately modulated mullite

• Applicant: Professor Dr. Reinhard X. Fischer
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2010 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 186441782

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.

• DFG Programme: Research Grants
• International Connection: Czech Republic, Taiwan
• Participating Persons: Professor Dr. Chuin-Shan Chen; Dr. Vaclav Petricek; Professor Dr. Hartmut Schneider