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A Hanawalt Type Phase Identification Procedure for a Minicomputer

  • Robert L. Snyder (a1)

Extract

The use of computers to aid in the identification of phases from their powder diffraction patterns was pioneered in the mid 1960's by Frevel, Nichols and Johnson (1-3). Today's most widely used Johnson algorithm conducts a reverse sequential search by comparing each reference pattern in the JCPDS powder diffraction file (PDF) to the unknown pattern. A figure of merit is computed for each match and the patterns with the best figures of merit are listed at the end of the search. The Nichols approach is a reverse search of a singly inverted reference file. An inverted file is one which stores the reference patterns according to the d value of the lowest angle 100% intensity line (d1) . This type of file is analogous to the Hanawalt search books distributed by the JCPDS for manual searching. When an inverted file is stored in a random format, along with suitable disk directory files, only reference patterns containing d1 values of interest need be read in the search.

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References

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1. Frevel, L.K., “Computational Aids for Identifying Crystalline Phases by Powder Diffraction,” Anal. Chem. 37:471482 (1965).
2. Nichols, M.C., “A Fortran II Program for the Identification of X-ray Powder Diffraction Patterns,” UCRL-70078, Lawrence Livermore Laboratory, Oct. 1966,
3. Johnson, G.G. and Vand, V., “A Computerized Powder Diffraction Identification System,” Ind. Eng. Chern. 59:1931 (1967).
4. Snyder, R.L., Johnson, Q.C., Kahara, E., Smith, G.S. and Nichols, M.C., “An Analysis of the Powder Diffraction File,” DCRL-52505, Lawrence Livermore Laboratory, June 1978.
5. Frevel, L.K., Adams, C.E. and Ruhberg, L.R., “A Fast Search Program for Powder Diffraction Analysis,” J. Appl. Cryst. 9:300305 (1976).
6. Mallory, C.L. and Snyder, R.L., “The Alfred University X-ray Powder Diffraction Automation System,” N.Y.S. College of Ceramics Technical Paper 144 (1979).
7. Jenkins, R. and Hubbard, C.R., “A Preliminary Report on the Design and Results of the Second Round-Robin to Evaluate Search/Match Methods for Quantitative Powder Diffractometry,” Adv. X-ray Anal. 22:133142 (1979).

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