Hostname: page-component-586b7cd67f-2brh9 Total loading time: 0 Render date: 2024-11-24T16:23:49.075Z Has data issue: false hasContentIssue false
  • English
  • Français

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
Get access Rights & Permissions [Opens in a new window]

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

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bish, D. L., and Reynolds, R. C. Jr. (1989). “Sample preparation in x-ray diffraction,” in Reviews in Mineralogy, Modern Powder Diffraction, Vol. 20, edited by D. L. Bish and J. E. Post (Mineralogical Society of America, Washington), pp. 73–99.Google Scholar
Francombe, M. H., and Lewis, B. (1958). “Structural and electrical properties of silver niobate and silver tantalate,” Acta Crystallogr. 11, 175–178.CrossRefGoogle Scholar
Glazer, A. M. (1972). “The classification of tilted octahedra in perovskites,” Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. B28, 3384–3392.CrossRefGoogle Scholar
Glazer, A. M., and Megaw, H. D. (1973). “Studies of the lattice parameters and domains in the phase transitions of NaNbO 3,”Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. A29, 489–495.CrossRefGoogle Scholar
Langford, J. I. (1971). “Powder pattern programs,” J. Appl. Crystallogr. 4, 259–260.CrossRefGoogle Scholar
Langford, J. I. (1998). Private communication.Google Scholar
Lukaszewski, M., Pawelczyk, M., Handerek, J., and Kania, A. (1983). “On the phase transitions in silver niobate AgNbO 3,”Phase Transit. 3, 247–258.CrossRefGoogle Scholar
Reisman, A., and Holtzberg, F. (1958). “Heterogeneous equilibria in the systems Li 2O-Ag 2O–Nb 2O 5 and oxide-models,” J. Am. Chem. Soc. 80, 6503–6507.CrossRefGoogle Scholar
Sakowski-Cowley, A. C., Lukaszewicz, K., and Megaw, H. D. (1969). “The structure of sodium niobate at room temperature, and the problem of reliability in pseudosymmetric structures,” Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. B25, 851–865.CrossRefGoogle Scholar
Smith, G. S., and Snyder, R. L. (1979). “F N: a criterion for rating powder diffraction patterns and evaluating the reliability of powder-pattern indexing,” J. Appl. Crystallogr. 12, 60–65.CrossRefGoogle Scholar
Verwerft, M., van Tendeloo, G., van Landuyt, J., Coene, W., and Amelinckx, S. (1988). “Trial model for the tilting scheme in AgNbO 3 derived by electron diffraction and imaging,” Phys. Status Solidi A 109, 67–78.CrossRefGoogle Scholar