Characterization of Bi5Nb3O15 by refinement of neutron diffraction pattern, acid treatment and reaction of the acid-treated product with n-alkylamines |
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Authors: | Seiichi Tahara Nobuhiro Kumada |
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Affiliation: | a Department of Applied Chemistry, School of Science and Engineering, Waseda University, 3-4-1, Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan b Department of Research Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Miyamae-cho 7, Kofu 400-8511, Japan |
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Abstract: | The structure of Bi5Nb3O15 was investigated by refinement of the powder neutron diffraction pattern as well as by structural change through acid treatment and subsequent treatments of an acid-treated product with n-alkylamines. Rietveld refinement suggests that Bi5Nb3O15 adopts a mixed-layer Aurivillius-related phase structure, [Bi2O2]+[NbO4]+[Bi2O2]+[BiNb2O7] [Pnc2 (space group No. 30)] with a=2.1011(4), b=0.5473(1) and c=0.5463(1) nm. After the acid treatment of Bi5Nb3O15 with 3 mol/L HCl, a new reflection (at 2.25 nm after drying at room temperature or at 1.89 nm after drying at 120 °C) appeared in the X-ray diffraction (XRD) pattern in addition to the reflections due to Bi5Nb3O15. Upon acid treatment, a part of the Bi ions were lost and essentially no Nb ions were dissolved during acid treatment to give a Bi/Nb molar ratio of 1.4. The TG curves of the acid-treated product showed mass loss (ca. 4 mass%) in the range of 300-600 °C. It was also demonstrated that the particle shapes did not change upon acid treatment. The reaction of the acid-treated product (after drying at room temperature) with n-alkylamines led to a shift of the newly appearing reflection to a lower angle, and the d-value of the low-angle reflection increased linearly in accordance with the increment of the number of carbon atoms in n-alkylamines. These results indicate that the [Bi2O2] sheet in Bi5Nb3O15 was partially leached by acid treatment to form a layered compound H4BiNb3O11·xH2O, capable of accommodating n-alkylamines in the interlayer space, and its anhydrous form, H4BiNb3O11, upon drying. Based on the variation in the interlayer distance upon intercalation of n-alkylamines into the acid-treated product, the structure of the acid-treated product can be suggested to comprise alternately stacked protonated [BiNb2O7] and [NbO4] sheets, a result consistent with the Rietveld refinement of Bi5Nb3O15. |
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Keywords: | Aurivillius phase Neutron diffraction Crystal structure Layered perovskite Intergrowth Acid treatment Intercalation Ion exchange |
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