Elucidating structural order and disorder phenomena in mullite-type Al4B2O9 by automated electron diffraction tomography

作者：Zhao Haishuang; Krysiak Yasar; Hoffmann Kristin; Barton Bastian; Molina Luna Leopoldo; Neder Reinhard B; Kleebe Hans Joachim; Gesing Thorsten M; Schneider Hartmut; Fischer Reinhard X; Kolb Ute^*

来源：Journal of Solid State Chemistry, 2017, 249: 114-123.

DOI：10.1016/j.jssc.2017.02.023

• Electron diffraction
• Aluminum borate
• Crystal structure determination
• Superstructure
• Disorder

The crystal structure and disorder phenomena of Al4B2O9, an aluminum borate from the mullite-type family, were studied using automated diffraction tomography (ADT), a recently established method for collection and analysis of electron diffraction data. Al4B2O9, prepared by sol-gel approach, crystallizes in the monoclinic space group C2/m. The ab initio structure determination based on three-dimensional electron diffraction data from single ordered crystals reveals that edge-connected AlO6 octahedra expanding along the b axis constitute the backbone. The ordered structure (A) was confirmed by TEM and HAADF-STEM images. Furthermore, disordered crystals with diffuse scattering along the b axis are observed. Analysis of the modulation pattern implies a mean superstructure (AAB) with a threefold b axis, where B corresponds to an A layer shifted by 1/2a and 1/2c. Diffraction patterns simulated for the AAB sequence including additional stacking disorder are in good agreement with experimental electron diffraction patterns.

• 出版日期2017-5