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Fundamentals of Rietveld Refinement I. XRD Pattern Simulation. An Introduction to Rietveld Refinement using PANalytical X’Pert HighScore Plus v3.0d Scott A Speakman, Ph.D. MIT Center for Materials Science and Engineering firstname.lastname@example.org. Outline.
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An Introduction to Rietveld Refinement
PANalyticalX’PertHighScore Plus v3.0d
Scott A Speakman, Ph.D.
MIT Center for Materials Science and Engineering
Bragg’s Law: λ= 2dhklsinθ
The atomic scattering factor f0 can be found using tables or equations determined experimentally or from quantum mechanical approximations
site occupancy factor, sof, is equivalent to N in the Fhkl equation
The symmetry explorer allows you to choose the space group and a specific origin, and to see information about the symmetry elements and special positions
k is the angle between the preferred orientation vector and the normal to the planes generating the diffracted peak
r is a refinable parameter in the Rietveld method
we will explore using the correction in our refinement on Tuesday
We now know how to calculate the diffraction peak intensity, but there a couple of more factors involved in simulating real diffraction data
mass absorption coefficient (sample transparency)
defect concentrationDiffraction peaks have profiles that must be empirically modeled
Rietveld refinement assumes that peak profiles vary systematically as a function of 2theta
Peak profile may also vary according to crystallographic direction [hkl]
Gaussian profile shape
Lorentzian profile shape
refinement of a polynomial function
refinement using a type I or II Chebyshev polynomial function
By amorphous sinc function
linear interpolation between base points
independent data collection run without the sample in place
Global parameters affect the entire sample rather than individual phases
POL (lorentz polarization factor)
selecting the Profile Function
Other parameters are set individually for each phase
preferred orientation (March-Dollase function)
atomic parameters are for each atom in the phase
position, SOF, thermal parameter
Peak Profile parameters
Cagliotti peak width function parameters U,V, and W
Profile shape parameters
peak asymmetry profile
anisotropic broadening function