Combining 27Al Solid-State NMR and First-Principles Simulations To Explore Crystal Structure in Disordered Aluminum Oxynitride

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• 作者：Bingtian Tu ; Xin Liu ; Hao WangWeimin Wang ; Pengcheng Zhai ; Zhengyi Fu
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：December 19, 2016
• 年：2016
• 卷：55
• 期：24
• 页码：12930-12937
• 全文大小：414K
• ISSN：1520-510X

文摘

The nuclear magnetic resonance (NMR) technique gives insight into the local information in a crystal structure, while Rietveld refinement of powder X-ray diffraction (PXRD) sketches out the framework of a crystal lattice. In this work, first-principles calculations were combined with the solid-state NMR technique and Rietveld refinement to explore the crystal structure of a disordered aluminum oxynitride (γ-alon). The theoretical NMR parameters (chemical shift, δ_iso, quadrupolar coupling constants, C_Q, and asymmetry parameter, η) of Al_22.5O_28.5N_3.5, predicted by the gauge-including projector augmented wave (GIPAW) algorithm, were used to facilitate the analytical investigation of the ²⁷Al magic-angle spinning (MAS) NMR spectra of the as-prepared sample, whose formula was confirmed to be Al_2.811O_3.565N_0.435 by quantitative analysis. The experimental δ_iso, C_Q, and η of ²⁷Al showed a small discrepancy compared with theoretical models. The ratio of aluminum located at the 8a to 16d sites was calculated to be 0.531 from the relative integration of peaks in the ²⁷Al NMR spectra. The occupancies of aluminum at the 8a and 16d positions were determined through NMR investigations to be 0.9755 and 0.9178, respectively, and were used in the Rietveld refinement to obtain the lattice parameter and anion parameter of Al_2.811O_3.565N_0.435. The results from ²⁷Al NMR investigations and PXRD structural refinement complemented each other. This work provides a powerful and accessible strategy to precisely understand the crystal structure of novel oxynitride materials with multiple disorder.