International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 2.4, pp. 81-82

Section 2.4.1.6. Unknown-phase identification: databases

J. M. Cowleya

2.4.1.6. Unknown-phase identification: databases

| top | pdf |

To a limited extent, the compilations of data for X-ray diffraction, such as the ICDD Powder Diffraction File, may be used for the identification of phases from electron diffraction data. The nature of the electron diffraction data and the circumstances of its collection have prompted the compilation of databases specifically for use with electron diffraction. Factors taken into consideration include the following.

  • (a) Because of the increasing use of single-crystal patterns obtained in the SAED mode in an electron microscope, the use of single-crystal spot patterns, in addition to powder patterns, must be considered for purposes of identification. Methods for the analysis of single-crystal patterns are summarized in Section 5.4.1[link] .

  • (b) The deviations from kinematical scattering conditions may be large, especially for single-crystal patterns, so that little reliance can be placed on relative intensities, and reflections kinematically forbidden may be present.

  • (c) Compositional information may be obtained by use of X-ray microanalysis (or electron-energy-loss spectroscopy) performed in the electron microscope and this provides an effective additional guide to identification.

  • (d) Electron diffraction data often extend to smaller d spacings than X-ray data because there is no wavelength limitation.

  • (e) The electron diffraction d-spacing information is rarely more precise than 1% and the uncertainty may be 5% for large d spacings.

With these points in mind, databases specially designed for use with electron diffraction have been developed. The NIST/Sandia/ICDD Electron Diffraction Database follows the design principles of Carr, Chambers, Melgaard, Himes, Stalick & Mighell (1987[link]). The 1993 version contains crystallographic and chemical information on over 81 500 crystalline materials with, in most cases, calculated patterns to ensure that diagnostic high-d-spacing reflections can be matched. It is available on magnetic tape or floppy disks. The MAX-d index (Anderson & Johnson, 1979[link]) has been expanded to 51 580 NSI-based entries (Mighell, Himes, Anderson & Carr, 1988[link]) in book form for manual searching.

References

Anderson, R. & Johnson, G. G. Jr (1979). The MAX-d alphabetical index to the JCPDS data base: a new tool for electron diffraction analysis. 37th Annu. Proc. Electron Microsc. Soc. Am., edited by G. W. Bailey, pp. 444–445. Baton Rouge: Claitors.
Carr, M. J., Chambers, W. F., Melgaard, D. K., Himes, V. L., Stalick, J. K. & Mighell, A. D. (1987). NBS/Sandia/ICDD Electron Diffraction Data Base. Report SAND87-1992-UC-13. Sandia National Laboratories, Albuquerque, NM 87185, USA.
Mighell, A. D., Himes, V. L., Anderson, R. & Carr, M. J. (1988). d-spacing and formula index for compound identification using electron diffraction. 46th Annu. Proc. Electron Microsc. Soc. Am., edited by G. W. Bailey, pp. 912–913. San Francisco Press.








































to end of page
to top of page