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Crystal Chemistry and Crystallography of the Aurivillius Phase Bi5AgNb4O18



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


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 Bi3TiNbO18 and Bid5^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+ (Am-1BmO3m+1)u2-^ (where A=Bi, and B= (AG, Nb)), which is characterized by perovskite-like (Am1BmO3m+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.
Journal of Solid State Chemistry


aurivillius phase, Bi<sub>5</sub>AgNb<sub>4</sub>O<sub>18</sub>, neutron powder diffraction, reference diffraction pattern, rietveld refinement, x-ray powder diffraction


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 Bi<sub>5</sub>AgNb<sub>4</sub>O<sub>18</sub>, Journal of Solid State Chemistry (Accessed May 28, 2024)


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Created October 18, 2004, Updated February 19, 2017