
Introduction: Rietveld refinement of Xray powder diffraction data can yield considerable amount of crystallographic information, in addition to quantitative phase estimation. The Rietveld method is a whole pattern fitting least squares technique and uses the entire pattern rather than a limited number of reflections to extract required information. In this method, the observed pattern for each phase is compared with the calculated one(modeled using single crystal structural data), and any differences between the two are minimized by refining structural as well as profile related parameters. Since the method uses all lines, severely overlapping reflections are not a problem. The method can obtain the following crystallographic information from data collected on any type of Xray diffractometer.
Lattice parameters Since systematic errors (for example, sample displacement) are refined during the refinement, accurate values up to one part in 1000 can be obtained on solid samples without an internal standard. Additionally, accurate cell dimensions can be computed on low symmetry materials.
Accurate phase quantification Scale factors are refined and are related to weight percentage of each phase. Complex mixtures with phases containing overlapping reflections are quantified with a high degree of accuracy (~2 wt.%)
Crystallite size and strain A mathematical function is used to model the profiles and to separate diffraction peak broadening due to size from that due to strain. Size and microstrain values are derived simultaneously from the XRD pattern.
Site occupancies Yields quantitative information as to the extent of solid solution or isomorphous substitution (Zr to Ti).
Preferred orientation Since preferred orientation on a unique axis can be refined, a relative measure of degree of orientation can be obtained.


