Rietveld and Pair distribution function (PDF) analysis workshop

Course description:Â In crystallography, the Rietveld method revolutionized the way in which we study the structure of materials to understand their properties. It is the aim of this intensive course to impart the Rietveld method in theory and practice. Using selected examples the entire process from profile fitting using fundamental parameters towards crystal structure determination and refinement will be explained. Now more than ever, it is important to consider structure characterization methods for nanostructured and amorphous materials that diffract poorly. This workshop will also serve as an introduction to the pair distribution function (PDF) method, a technique for determining the local structure in disordered materials. We will cover the basic theory of the method, data processing, and an in-depth tutorial on structure refinement implemented in TOPAS v.7.Â

In particular, the following topics will be covered:Â

ï‚· Basics of powder diffraction and Rietveld Refinement

ï‚· The profile of a Bragg reflection

ï‚· Determination of the Instrument Resolution Function (IRF) for powder diffractometers

ï‚· Whole Powder Pattern-Fitting techniques (WPPF)

ï‚· The intensity of a Bragg reflection

ï‚· Correction factors for diffraction angles and intensity

ï‚· Methods to develop a starting model for crystal structure determination

ï‚· Penalty-functions, constraints, restraints

ï‚· Rigid Bodies (RB) (flexible polyhedra, molecules, z-matrices)

 Strategies for structure determination, global optimization in direct space, Charge-Flipping (CF)

ï‚· Difference-Fourier-analysis in combination with Rietveld refinement

ï‚· Isotropic and anisotropic microstructural parameters

ï‚· Using the ICDD PDF5+ database for phase identification and str file export

ï‚· Quantitative Phase Analysis (QPA)

ï‚· Different methods for quantifying the amorphous content

ï‚· Alternative ways of describing crystal structures

ï‚· Sequential and parametric Rietveld refinementsÂ

ï‚· Stacking faulted superstructures

ï‚· The making of Rietveld-Plots for publication

ï‚· Basics of total scattering and pair distribution function analysis

ï‚· Obtaining the pair distribution function from total scattering data

ï‚· Determining and accounting for effects of instrumental resolution

ï‚· Small-box crystal structure refinement

ï‚· Modelling nanoparticle structures and particle size distributions

ï‚· Simulated annealing and large-box approachÂ

Main tutors:Â

Sebastian Bette (MPI-FKF), Robert E. Dinnebier (MPI-FKF), Martin Etter (DESY), John Evans (Uni. Durham), Paolo Scardi (Uni. Trento), Maxwell W. Terban (Momentum Transfer)Â Â