Characterization of Bi5Nb3O15 by refinement of neutron diffraction pattern, acid treatment and reaction of the acid-treated product with n-alkylamines

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] [Pnc  2 (space group No. 30)] with a=2.1011(4)a=2.1011(4), b=0.5473(1)b=0.5473(1) and c=0.5463(1)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.

Crystal structure of Bi5Nb3O15 is investigated by refinement of neutron diffraction pattern as well as by structural change through acid treatment of Bi5Nb3O15 and subsequent treatment of an acid-treated product with n-alkylamine.Figure optionsDownload as PowerPoint slide