Abstracts Book - IMRC 2018

• SD6-O012 Invited Talk
SIZE EFFECTS IN DIFFRACTION ANALYSIS OF NANOCRYSTALLINE
POWDER SAMPLES
Ismail Noyan 1
1 Columbia University in the City of New York, Dept. of Appl. Phys. & Appl. Math., United States.
Most formalisms utilized for diffraction analysis of the structure of
nanocrystalline powder samples are based on basic concepts developed over
the past century. Commercial or open-source programs based on these
formalisms are included with most laboratory-based diffraction systems. In
most of these codes the algorithms used for the propagation of errors
associated with the computed structural parameters are not explicitly described
but, in general, these are based on photon counting statistics and peak-fits. This
approach can cause problems in determining the degree of uncertainty of
published results, since for non-ideal samples both photon statistics and Bragg
sampling influence the measured Bragg peak intensities [1]. In the past decade
we have used rigorous forward modelling of diffraction powder samples to
investigate the diffraction process [2-4]. Our simulations showed that the
sampling rules and statistics for powder diffraction, and concepts like reflection
multiplicity, the “Lorentz factor”, sampling statistics, etc. are different when the
diffraction signal originates nanocrystalline powders. In this lecture we will
discuss these results and show that quantifying uncertainty budgets for powder
diffraction experiments through rigorous forward modeling is essential for
understanding the data x-ray diffraction experiments.
References
[1] Alexander L. et. al., “Statistical Factors Affecting the Intensity of X-Rays
Diffracted by Crystalline Powders”, Journal of Applied Physics, 19, 1948.
[2] Öztürk H., Yan H., Hill, J. P., Noyan I. C. , “Sampling Statistics of Diffraction
Nanoparticle Powder Aggregates”, Journal of Applied Crystallography, 47,
2014.
[3] Öztürk H., Yan H., Hill J. P., Noyan I.C., “Correlating Sampling and Intensity
Statistics In Nanoparticle Diffraction Experiments”, Journal of Applied
Crystallography, 48, 2015.
[4] Öztürk H., and Noyan, I. C., “Expected Values and Variances Of Bragg Peak
Intensities Measured In a Nanocrystalline Powder Diffraction Experiment”,
Journal of Applied Crystallography, 50, 2017.