Crystal Chemistry and Crystallography of the Aurivillius Phase Bi5AgNb4O18

Published

October 18, 2004

Author(s)

Winnie K. Wong-Ng, Qingzhen Huang, Lawrence P. Cook, Igor Levin, James A. Kaduk, Alan D. Mighell, J Suh

Abstract

Bi₅AgNb₄O₁₈ is a new phase, which was discovered during the phase equilibrium study of the Bi₂O₃-Ag₂O-Nb₂O₅ system. Bi₅AgNb₄O₁₈ was prepared at 750 C and is stable in air up to its melting temperature of 1160.1 5.0 C. Results of a Rietveld refinement using neutron powder diffraction confirmed that Bi₅AgNb₄O₁₈ is is structural with Bi₃TiNbO_{18 and Bi}d5^KNb₄O₁₈. The structure was refined in the orthorhombic space group A2₁am, Z=2, and the lattice parameters are a = 5.4915 (2) , b=5.4752(2) , c=24.9232(8) , V = 749.52 (4) ³. The structure can be described as the m=2 member of the Aurivillius family, (Bi₂O₂)²⁺ (A_m-1B_mO_3m+1)u2-^ (where A=Bi, and B= (AG, Nb)), which is characterized by perovskite-like (A_m1B_mO_3m+1)^2- slabs regularly interleaved with (Bi₂O₂)²⁺ layers. The octahedral [NbO₆] units are tilted about the a- and c-axis by about 10.3 and 12. 4 , respectively. Ag was found to substitute exclusively into the Bi site that is located in the layer between the two distorted [NbO₆] units. Although the Ag substitutes into the Bi-site with the Bi: Ag ratio of 1:1, the existence of a superlattice was not detected using electron diffraction. A comparison of Bi₅MNb₄O₁₈ structures (where M=Ag, Na and K) revealed a relation between the size of the M-cation and structural distortion. The reference pattern for Bi₅AgNb₄O₁₈ has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File.

Citation

Journal of Solid State Chemistry

Volume

177

Issue

10

Pub Type

Journals

Keywords

aurivillius phase, Bi₅AgNb₄O₁₈, neutron powder diffraction, reference diffraction pattern, rietveld refinement, x-ray powder diffraction

Citation

Wong-Ng, W. , Huang, Q. , Cook, L. , Levin, I. , A., J. , Mighell, A. and Suh, J. (2004), Crystal Chemistry and Crystallography of the Aurivillius Phase Bi₅AgNb₄O₁₈, Journal of Solid State Chemistry (Accessed April 27, 2024)