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Accuracy in Quantitative X-ray Powder Diffraction Analyses

Published online by Cambridge University Press:  06 March 2019

D. L. Bish  and
Steve. J. Chipera
D. L. Bish
Affiliation:
Geology and Geochemistry, MS D469 Los Alamos National Laboratory Los Alamos, NM 87545
Steve. J. Chipera
Affiliation:
Geology and Geochemistry, MS D469 Los Alamos National Laboratory Los Alamos, NM 87545
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Abstract

Accuracy, or how well a measurement conforms to the true value of a parameter, is important in XRD analyses in three primary areas, 1) 26 position or d-spacing; 2) peak shape; and 3) intensity. Instrumental factors affecting accuracy include zero-point, axial-divergence, and specimen- displacement errors, step size, and even uncertainty in X-ray wavelength values. Sample factors affecting accuracy include specimen transparency, structural strain, crystallite size, and preferred orientation effects. In addition, a variety of other sample-related factors influence the accuracy of quantitative analyses, including variations in sample composition and order/disorder. The conventional method of assessing accuracy during experimental diffractometry measurements is through the use of certified internal standards. However, it is possible to obtain highly accurate d-spacings without an internal standard using a well-aligned powder diffractometer coupled with data analysis routines that allow analysis of and correction for important systematic errors. The first consideration in such measurements is the use of methods yielding precise peak positions, such as profile fitting. High accuracy can be achieved if specimen-displacement, specimen- transparency, axial-divergence, and possibly zero-point corrections are included in data analysis. It is also important to consider that most common X-ray wavelengths (other than Cu Kα1) have not been measured with high accuracy. Accuracy in peak-shape measurements is important in the separation of instrumental and sample contributions to profile shape, e.g., in crystallite size and strain measurements. The instrumental contribution must be determined accurately using a standard material free from significant sample-related effects, such as NIST SRM 660 (LaB6). Although full-pattern fitting methods for quantitative analysis are available, the presence of numerous systematic errors makes the use of an internal standard, such as a-alumina mandatory to ensure accuracy; accuracy is always suspect when using external-standard, constrained-total quantitative analysis methods. One of the most significant problems in quantitative analysis remains the choice of representative standards. Variations in sample chemistry, order-disorder, and preferred orientation can be accommodated only with a thorough understanding of the coupled effects of all three on intensities. It is important to recognize that sample preparation methods that optimize accuracy for one type of measurement may not be appropriate for another. For example, the very fine crystallite size that is optimum for quantitative analysis is unnecessary and can even be detrimental in d-spacing and peak shape measurements.

Type
II. Phase Analysis, Accuracy and Standards in Powder Diffraction
Information
Advances in X-Ray Analysis , Volume 38: Forty-third Annual Conference on Applications of X-ray Analysis , 1994 , pp. 47 - 57
Copyright
Copyright © International Centre for Diffraction Data 1994

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References

American Heritage Dictionary (1985) Houghton Mifflin Co., Boston, 73.Google Scholar
Beardon, J. A. (1974) X-ray wavelengths. International Tables for X-ray Crystallography, Vol. IV, The Kynoch Press, Birmingham, 6–43.Google Scholar
Bish, D. L., and Chipera, S. J. (1988) Problems and solutions in quantitative analysis of complex mixtures by X-ray powder diffraction. Adv. X-ray Anal., 31, 295–307.Google Scholar
Bish, D. L., and Howard, S. A. (1988) Quantitative phase analysis using the Rietveld method. J. Appl. Cryst., 21, 86–91.Google Scholar
Bish, D. L., and Post, J. E. (1993) Quantitative mineralogical analysis using the Riets'eld full-pattern fitting method, Amer. Mineral, 78, 932–940.Google Scholar
Bish, D. L., and Reynolds, R. C, Jr. (1989) Sample Preparation for X-ray Diffraction. Chap. 4 in Bish, D. L. and Post, J. E., eds., Modem Powder Diffraction. Mineralogical Society of America, Reviews in Mineralogy, 20, 73–99.Google Scholar
Bish, D. L., and Von Dreele, R. B. (1989) Rietveld refinement of non-hydrogen atomic positions in kaohnite. Clays & Clay Minerals, 37, 289–296.Google Scholar
Burnham, C. W. (1991) LCLSQ: Lattice parameter refinement using corrections terms for systematic errors, American Mineralogist, 76, 663–664.Google Scholar
Chipera, S. J., and Bish, D. L. (1995) Multireflection RIR and intensity normalizations for quantitative analyses: Applications to feldspars and zeolites. Powder Diffr., 10, in press.Google Scholar
Davis, B. L., and Smith, D. K. (1988) Tables of experimental reference intensity ratios. Powder Diffr., 3, 205–208.Google Scholar
Davis, B. L., Smith, D. K., and Holomany, M. A. (1989) Tables of experimental reference intensity ratios. Table No. 2, December 1989. Powder Diffr., 3, 205–208.Google Scholar
Deslattes, R. D. and Henins, A. (1973) X-ray to visible wavelength ratios. Phys. Rev. Letters, 31, 972–975.Google Scholar
Ghiorso, M. S., Carmichael, I. S. E., and Moret, L. K. (1979) Inverted high-temperature quartz, Contrib. Mineral. Petrol., 68, 307–323.Google Scholar
Hill, R. J., and Howard, C. J. (1987) Quantitative phase analysis from neutron powder diffraction data using the Rietveld method. J. Appl. Cryst., 9, 169–174.Google Scholar
Howard, S. A., and Snyder, R. L. (1589) The use of direct convolution products in profile and pattern fitting algorithms. I: Devslopment of the algorithms. J. Appl. Cryst., 22, 238–243.Google Scholar
Hurst, V. J., and Storch, S. P. (1981) Regional variation in the cell dimensions of metamorphic quartz. Amer Mineral., 66, 204–212.Google Scholar
Jenkins, R. (1983) Effects of diffractometer alignment and aberrations on peak positions and intensities. Adv. X-ray Anal., 26, 25–33.Google Scholar
Parrish, W, and Huang, T C. (1983) Accuracy and precision of intensities in X-ray polycrystalline diffraction. Adv. X-ray Anal., 26, 35–44.Google Scholar
Smith, D. K., Johnson, G. G., Scheible, A., Wims, A. M., Johnson, J. L., and Ullmann, G. (1987) Quantitative X-ray powder diffraction method using the full diffraction pattern. Powder Diffr., 2, 73–77.Google Scholar
Snyder, R. L. (1983) Accuracy in angle and intensity measurements in X-ray powder diffraction. Adv. X-ray Anal., 26, 1–10.Google Scholar
Suortti, E (1977) Accuracy of structure factors from X-ray powder intensity measurements. Acta Cryst., A33, 1012–1027.Google Scholar
Taylor, J. C., and Matulis, C. E. (1991) Absorption contrast effects in the quantitative XRD analysis of powders by full multiphase profile refinement. J. Appl. Cryst., 24, 14–17.Google Scholar
Wilson, A.J. C. (1980) Accuracy in methods of lattice-parameter measurement. Accuracy in Powder Diffraction, National Bureau of Standards Special Publication 567, 325–351.Google Scholar