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.
, Huang, Q.
, Cook, L.
, Levin, I.
, A., J.
, Mighell, A.
and Suh, J.
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 December 8, 2023)