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Accurate Modeling of Size and Strain Broadening in the Rietveld Refinement: The “Double-Voigt” Approach

Published online by Cambridge University Press:  06 March 2019

Davor Baizar  and
Hassel Ledbetter
Davor Baizar
Affiliation:
Department of Materials Research and Electronics, Ruder Boškovič Institute PO. Box 1016, 41001 Zagreb, Croatia
Hassel Ledbetter
Affiliation:
Materials Science and Engineering Laboratory, National Institute of Standards and Technology, 325 Broadway, BoulderColorado 80303, U.S.A.
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Abstract

In the “double-Voigt” approach, an exact Voigt function describes both size- and strainbroadened profiles. The lattice strain is defined in terms of physically credible mean-square strain averageid over a distance in the diffracting domains. Analysis of Fourier coefficients in a harmonic approximation for strain coefficients leads to the Warren-Averbach method for the separation of size and strain contributions to diffraction line broadening. The model is introduced in the Rietveld refinement program in the foliowing way: Line widths are modeled with only four parameters in the isotropic case. Varied parameters are both surface- and volumeweighted domain sizes and root-mean-square strains averaged over two distances. Refined parameters determine the physically broadened Voigt line profile. Instrumental Voigt line profile parameters are added to obtain the observed (Voigt) line profile. To speed computation, the corresponding pseudo-Voigt function is calculated and used as a fitting function in refinement. This approach allows for both fast computer code and accurate modeling in terms of physically identifiable parameters.

Type
V. Residual Stress, Crystallite Size and rms Strain Determination by Diffraction Methods
Information
Advances in X-Ray Analysis , Volume 38: Forty-third Annual Conference on Applications of X-ray Analysis , 1994 , pp. 397 - 404
Copyright
Copyright © International Centre for Diffraction Data 1994

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