1. Rietveld Refinement

2. Why do Reitveld Refinement?

3. What are the limitations of Rietveld?
Phase detection limit of 1-5%
Impurity atom determination
New/unknown crystal structures
Determination of disorder parameter
Multiple parameters can have same effect diffraction patterns
Equipment (powder vs. single crystal, x-rays vs. neutrons)
Garbage in, garbage out! (noisy data, poor quality sample, poor sample prep)

4. Basic refinement procedure
Background
Lattice parameters
Peak intensities
Peak shapes
Peak positions
Phase fractions
Experimental diffraction pattern
Starting crystal structure (.cif, ICSD)
Refinement program: GSAS, FullProf
Assess:
Goodness of fit/R factors
Impurity phases
Peak/background shapes
Difference pattern
Instrument file (.inst, LaB6 standard)

5. Some common challenges/problems
False minimas
Refinement diverges (“blows up”)
Which goodness of fit to choose? R vs. Chi sq?
Preferred orientation
Large amorphous background
Incorrect starting crystal structure or lattice parameter
Poor quality data!

6. Resources and links
GSAS/EXPGUI:
GSAS tutorials:
FullProf:
PowDLL (file conversion):
Lots of info about fitting parameters:
People: Lauryn Baranowski Lakshmi Krishna