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Effect of Powder Sample Granularity on Fluorescent Intensity and on Thermal Parameters in X-Ray Diffraction Rietveld Analysis

Published online by Cambridge University Press:  06 March 2019

C. J. Sparks ,
R. Kumar ,
E. D. Specht ,
P. Zschack ,
G. E. Ice ,
T. Shiraishi  and
K. Hisatsune
C. J. Sparks
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
R. Kumar
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
E. D. Specht
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
P. Zschack
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
G. E. Ice
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
T. Shiraishi
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
K. Hisatsune
Affiliation:
Oak Ridge National Laboratory P.O. Box 200S Oak Ridge, Tennessee 37831-6118
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Abstract

The effect of sample granularity on diffracted x-ray intensity was evaluated by measuring the 2θ dependence of x-ray fluorescence from various samples. Measurements were made in the symmetric geometry on samples ranging from single crystals to highly absorbing coarse powders. A characteristic shape for the absorption correction was observed. A demonstration of the sensitivity of Rietveld refined site occupation parameters is made on CuAu and Cu50Au44Ni6 alloys refined with and without granularity corrections. These alloys provide a good example of the effect of granularity due to their large linear x-ray absorption coefficients. Sample granularity and refined thermal parameters obtained from the Rietveld analysis were found to be correlated. Without a granularity correction, the refined thermal parameters are too low and can actually become negative in an attempt to compensate for granularity, A general shape for granularity correction can be included in refinement procedures. If no granularity correction is included, data should be restricted to above 30° 2θ, and thermal parameters should be ignored unless extreme precautions are taken to produce <5 (μm particles and high packing densities.

Type
I. Whole Pattern Fitting, Rietveld Analysis and Calculated Diffraction Patterns
Information
Advances in X-Ray Analysis , Volume 35 , Issue A: First Pacific-International Congress on X-ray Analytical Methods (PICXAM). Fortieth Annual Conference on Applications of X-ray Analysis, August 7-16, 1991 , 1991 , pp. 57 - 62
Copyright
Copyright © International Centre for Diffraction Data 1991

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