Characterization of Bi 5Nb 3O 15 by refinement of neutron diffraction pattern, acid treatment and reaction of the acid-treated product with n-alkylamines

Abstract

The structure of Bi 5Nb 3O 15 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 Bi 5Nb 3O 15 adopts a mixed-layer Aurivillius-related phase structure, [Bi 2O 2]+[NbO 4]+[Bi 2O 2]+[BiNb 2O 7] [ 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 Bi 5Nb 3O 15 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 Bi 5Nb 3O 15. 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 [Bi 2O 2] sheet in Bi 5Nb 3O 15 was partially leached by acid treatment to form a layered compound H 4BiNb 3O 11· xH 2O, capable of accommodating n-alkylamines in the interlayer space, and its anhydrous form, H 4BiNb 3O 11, 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 [BiNb 2O 7] and [NbO 4] sheets, a result consistent with the Rietveld refinement of Bi 5Nb 3O 15.