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Advances in the Computer Indexing of Powder Patterns

Published online by Cambridge University Press:  06 March 2019

Gordon S. Smith
Gordon S. Smith*
Affiliation:
Chemistry and Materials Science Department, Lawrence Livermore Laboratory, University of California, Livermore, California 94550
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Abstract

Indexing of powder-diffraction patterns by computer techniques has advanced to the state that it is now often possible to determine unit-cell dimensions and crystal system for an unknown material solely from its powder-diffraction data. This indexing is fully automated, proceeding directly from positions of observed diffraction lines as input, with decision-making steps being made by a computer. Ease of indexing depends on quality of data (accuracy and completeness), volume of the unit cell, and symmetry of the crystal system. In general, a powder pattern of a triclinic compound with a large unit cell requires a more accurate and complete data-set for successful indexing than does a cubic material having a small unit cell. Fortunately, data from a well-aligned diffractometer or Guinier camera ordinarily suffices for computer indexing. Because of systematic errors in the low-lying diffraction lines, data from the Debye-Scherrer technique usually are not adequate for computer indexing (except for the simpler cases). A brief review of the strategies/algorithms of some of the computer indexing codes now available is given. Criteria for assessing the reliability of a particular computer- assisted indexing are discussed. Finally, attention is directed toward future developments such as by automating the collection of powder- diffraction data, analyzing data by computer data processing, and increasing the speed and reliability of computer indexing.

Type
Use of Computers in Powder Diffraction
Information
Advances in X-Ray Analysis , Volume 23: Twenty-Eighth Annual Conference on Applications of X-ray Analysis, July 30 - August 3, 1979 , 1979 , pp. 295 - 303
Copyright
Copyright © International Centre for Diffraction Data 1979

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References

1. Klug, H. P. and Alexander, L. E., X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials, J. Wiley and Sons (1974).Google Scholar
2. Shirley, R., Personal communication (1977).Google Scholar
3. Goebel, J. B. and Wilson, A. S., “INDEX, U.S* Atomic Energy Commission, Research and Development Report,” BNWL-22 (1965).Google Scholar
4. Visser, J. W., “A Fully Automatic Program for Finding The Unit Cell from Powder Data,” J. Appl. Cryst. 2, 89-95 (1969).Google Scholar
5. Roof, R. B., Jr., “INDEX, A Computer Program to Aid in the Indexing of X-ray Powder Patterns of Crystal Structures of Unknown Symmetry,” Los Alamos Scientific Laboratory Report, LA-3920 (1968).Google Scholar
6. Smith, G. S. and Kahara, E., “Automated Computer Indexing of Powder Patterns: the Monoclinic Case,” J. Appl. Cryst. 8, 681–683 (1975).Google Scholar
7. Smith, G. S. and E, Kahara, “Progress Toward Fast Indexing of Powder Patterns: High Symmetry Cases,” Paper PA20, American Crystallographic Association Winter Meeting, Norman, Oklahoma (1978).Google Scholar
8. de Wolff, P. M., “A Simplified Criterion for the Reliability of a Powder Pattern Indexing,” J. Appl. Cryst. 10, 108–113 (7968).Google Scholar
9. Smith, G. S. and Snyder, R. L., “Fy: A Criterion Powder Diffraction Patterns and Evaluating the Reliability of Powder-Pattern Indexing,” J. Appl. Cryst. 12, 60-65 (1979).Google Scholar
10. Smith, G. S., “Estimating Unit-Cell Volumes from Powder Diffraction Data: the Triclinic Case,” J. Appl. Cryst. 9, 424–428 (1976).Google Scholar
11. Smith, G. S., “Estimating the Unit-Cell Volume from One Line in a Powder Diffraction Pattern: the Triclinic Case,” J. Appl. Cryst. 10, 252–255 (1977).Google Scholar
12. Smith, G. S., “ Estimating Unit-Cell Volumes from Powder Diffraction Data: the Monoelinic and Orthorhorabic Cases,” unpublished.Google Scholar
13. Parrish, W., Huang, T. C., and Ayers, G. L., “ Profile Fitting: A Powerful Method of Computer X-ray Instrumentation and Analysis,” Transactions of the American Crystallographic Association 12, 55-73 (1976).Google Scholar