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An X-ray diffraction study of AgNbO3 and comparison with NaNbO3

Published online by Cambridge University Press:  10 January 2013

C. N. W. Darlington
C. N. W. Darlington
Affiliation:
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
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Abstract

The powder diffraction pattern of the perovskite AgNbO3 has been measured using CuKα1 radiation with an incident beam focusing monochromator to eliminate the Kα2 component. Indexing the pattern shows that the multipartite cell is 2×2×4 times that of the pseudocubic subcell. Comparison is made with the diffraction pattern of NaNbO3, which has a similar multipartite unit cell. There are strong similarities, but close inspection shows that the structures are not isomorphous. The paper concludes with a discussion of the figure of merit FN for pseudosymmetric structures. It is suggested that two figures of merit be reported. The first should be the standard one using either all measured reflections or just the first 30. The proposed second figure of merit does not include any superlattice reflections. These superlattice reflections tend to be very weak, resulting in a low completeness factor and relatively large error in the measurement of their position. This effect produces an unrealistically low value of the standard figure of merit. By including only “main” reflections, i.e., those reflections that are common to both the low-symmetry and high-symmetry parent phase (if it exists), a much better estimate of the quality of the fitting of the measured diffraction pattern is obtained.

Keywords

silver niobateperovskitepseudosymmetric structurepowder diffraction
Type
Research Article
Information
Powder Diffraction , Volume 14 , Issue 4 , December 1999 , pp. 253 - 257
Copyright
Copyright © Cambridge University Press 1999

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