Powder Diffraction and Rietveld School April 2018

The links below should take you to problems for different sessions of the school. This page can be launched from the jedit Help/General/Links menu. Use the links in jedit to access the topas wiki for more help or to find international tables etc.

Tutorials are arranged according to the sessions on your timetable. Early in the school please try and tackle the tutorials associated with each session. We don't expect you to complete all the tutorials; later in the school there will be time for you to tackle those problems most relevant to your research.

You should save relevant files in the folder "j:\school_work" (right click on links and use "save as". Once you've run i:\licence\rietveld\rietveld_setup.bat there will be a shortcut to this on your desktop.

Lecture notes and other useful files will be linked here. Old school photos are linked here.

Session 7/8 - Least Squares Refinement - Excel

These tutorials are intended to introduce you to least squares refinement. We'll use the solver function of excel to perform various least squares fits. We'll start fitting a straight line then move on to fitting Gaussians and eventually performing a full Rietveld refinement. We'll use topas academic to perform equivalent refinements to those in excel.

Tutorial 1 - Fitting straight lines, quadratics and Gaussians in excel. N.B. you may need to install "solver" in excel - go here.

Tutorial 2 - How to perform the same fits from Tutorial 1 in Topas.

Tutorial 3 - How to refine unit cell parameters in excel.

Tutorial 4 - How to perform Pawley and Rietveld refinements in excel.

Tutorial 5 - Indexing: How to index a tetragonal powder pattern and refine unit cell parameters using excel.

Session 8 - Peak Positions/Indexing

Peak positions are one of the fundamental aspects of a diffraction pattern and are determined by the cell size and shape. These tutorials look at how unknown unit cells are obtained/refined. You can try these procedures on any of the other data sets provided. If you've never used topas/jedit before you might want to try e.g. tutorial 8 or tutorial 9 first which go through some of the mechanics of using jedit in a bit more detail.

Tutorial 6 - Peak Fitting: How to perform individual peak fitting in topas, often the first step before indexing.

Tutorial 7 - Indexing: How to index a powder pattern in topas.

Session 10 - Instrument Alignment and Internal Standards

The tutorials below give you an idea of how to check your instrument alignment or how to use an internal standard to obtain both precise and accurate cell parameters..

Tutorial 7.5 - Calibrating diffractometer using nist al2o3 standard and how to compare intensities and positions in excel..

Tutorial 7.6 - To be written. How to apply a 2-theta correction polynomial to obtain accurate cell parameters..

Session 14 - TA/Simple Rietveld refinement in jedit/Topas Academic

The tutorials below are intended to give you an introduction to Rietveld and Pawley refinement using the topas academic/jedit interface. The aim of the tutorial session is not to necessarily fully understand what your doing, but to make sure you're happy with the "mechanics" of the overall process of Rietveld refinement.

If you want even more basic tutorials on topas/jedit then take a look at the introductory tutorials on the web. The examples there have far more detail and contain screen shots of (approximately) what you should see at each stage.

Tutorial 8 - How to run a prewritten input file.

Tutorial 9 - TiO2 Rietveld: A simple Rietveld refinement of lab data.

Tutorial 10 - TiO2 Rietveld starting from a template file.

Tutorial 11 - Pawley Fitting: Pawley fitting is a structure-independent whole-pattern fitting method. It's a good way of finding if a unit cell is correct and also finding the "best possible" fit you'd get by Rietveld.

Tutorial 12 - ZrW2O8 Rietveld: Simple Rietveld refinements of lab data, constant wavelength neutron and time of flight neutron data - make sure you have john's local.inc on your computer.

Tutorial 13 - Multiphase Rietveld refinement

Tutorial 13.5 - LaMnO3 Rietveld with no detailed instructions.

Session 15 - Neutron/Synchrotron/Combined Refinement

How to perform Rietveld/Pawley refinements using neutron/sychrotron data. As well as these examples you might want to repeat/complete the exercises from session 14.

Tutorial 14 - Y2O3 data recorded on id31 at the esrf

Tutorial 15 - ZrW2O8 Rietveld: Simple Rietveld refinements of lab data, constant wavelength neutron and time of flight neutron data - make sure you have john's local.inc on your computer. Note this is the same as tutorial 12 above.

Tutorial 16 - PbSO4 neutron data Jeremy discussed are here.

Tutorial 17 - Combined Refinement: Builds from earlier tutorial on ZrW2O8 and shows how to simultaneously fit X-ray and neutron data. Also discusses structure solution from X-ray and neutron data. See also gsas 3 and gsas 4.

Session 20 - Peak Shapes

Peak shapes are another fundamental aspect of a diffraction pattern. These tutorials investigate some of the functions used in Rietveld packages and how peak shapes can be used to give size/strain information.

Tutorial 18 - This tutorial explores convolutions to fit a single peak in a pattern using the convolution approach discussed in lectures.

Tutorial 19 - In this tutorial you'll investigate the various peak shape functions that are used in Rietveld refinement packages. You'll use experimental fwhm vs 2-theta data in excel to come up with functions that might describe a real data set. You'll then try these functions in topas.

Tutorial 20 - Fundamental Parameters peak shape fitting.

Tutorial 21 - Size/Strain Analysis: Shows how size/strain can be determined in topas using the CeO2 round robin data.

Tutorial 22 - Nanoparticle Sizing: Determines the size of ~2 nm particles from diffraction data.

Session 21 - Restraints/Rigid Bodies

Use of extra chemical information such as restraints and rigid bodies is often important when analysing powder data. Several of the tutorials (e.g. the one on ZrW2O8 Rietveld) use bond distance and angle restraints. Tutorials in this section provide more examples.

Tutorial 23 - Rietveld refinement of an organic molecule using restraints and rigid bodies. See also gsas 7.

Tutorial 24 - A complex use of rigid bodies to refine 3 molecules in asymmetric unit with z-matrix description of local bodies to constrain internal symmetry. Data recorded on id31.

Session 22 - Neutron and X-ray Combined Refinement

How to perform a combined refinement using neutron and X-ray data.

Tutorial 17 - Combined Refinement: Builds from earlier tutorial on ZrW2O8 and shows how to simultaneously fit X-ray and neutron data. Also discusses structure solution from X-ray and neutron data. See also gsas 3 and gsas 4.

Session 21/22/25 - GSAS/Fullprof Examples

These examples are similar to those you have/will perform in the topas tutorials and are designed to give you a feel for other widely used (and free) Rietveld packages. It's very important to use a range of software as different packages have different strengths. The packages come with many of their own built-in tutorials. The examples below deliberately repeat the analyses done in topas.

GSAS 1 - Y2O3 laboratory data

GSAS 2 - PbSO4 neutron data

GSAS 3 - ZrW2O8 neutron data

GSAS 4 - ZrW2O8 restraints and combined refinement

GSAS 5 - Sc2(WO4)3 rigid bodies

GSAS 6 - CFBr3 organic

GSAS 7 - A medium sized organic using restraints

GSAS 8 - NiL2 coordination compound with restraints

GSAS 9 - Quantitative Rietveld

GSAS 10 - Y2O3 in GSAS-II

Fullprof 1 - Y2O3 lab data in fullprof

Session 24 - Spot the Errors

These tutorials are designed to teach you how to trouble-shoot Rietveld refinements.

Tutorial 25 - Trouble shooting.

Session 25 - Structure Solution

Structure solution is not formally part of the course, but you could try the tutorials below if you're interested. The tutorial on combined refinement of ZrW2O8 also explores these ideas.

Tutorial 26 - Structure Solution of an inorganic oxide: Takes the information from earlier tutorials and solves the structure of TiO2 using simulated annealing.

Tutorial 27 - Structure solution of a rigid organic molecule and other examples.

Tutorial 28 - Structure solution of inorganic materials.

Session 25 - Miscellaneous Examples

Tutorial 29 - Quantitative Rietveld refinement. This is extremely important in many industries. This example uses the Round Robin data of Ian Madsen and Nikki Scarlett.

Tutorial 30 - Size/Strain Analysis: Shows how size/strain can be determined in topas using the CeO2 round robin data.

Tutorial 31 - Nanoparticle Sizing: Determines the size of ~2 nm particles from diffraction data.

Tutorial 32 - Solving a structure from single crystal data using charge flipping

Tutorial 33 - Single crystal: How to do a simple single crystal refinement in topas.

Tutorial 33.5 - Using functions in Topas v5 to explore the fundamental equations used in crystallographic refinement.

Session 25 - Parametric/Surface Refinement

Tutorial 33.7 - How to refine multiple datasets sequentially in v6 with #list format or v4/v5 with command files.

Tutorial 34 - Parametric or surface Rietveld refinement - how to use surface fitting to analyse 100 patterns simultaneously to follow phase transitions in WO3.

Tutorial 35 - Parametric or surface Rietveld refinement - how to refine temperature using the ZrP2O7 example.

Session 25 - Symmetry Mode Refinements

Tutorial 36 - Structural transformations. Directly refine symmetry-mode amplitudes rather than traditional atomic xyz coordinates of a distorted superstructure. Example based on simulated lab x-ray diffraction data from low-temperature orthorhombic LaMnO3. The symmetry modes are obtained using the ISODISTORT software.

Tutorial 37 - Structural transformations. Directly refine symmetry-mode amplitudes rather than traditional atomic xyz coordinates of a distorted superstructure. Example based on laboratory x-ray diffraction data from room-temperature monoclinic WO3. The symmetry modes are obtained using the ISODISTORT software.

Tutorial 38 - Structural transformations. A more advanced symmetry-mode refinement example based on room-temperature WO3. Fit both neutron and X-ray data. Try to determine space-group symmetry at high temperature using ISODISTORT.

Tutorial 41 - By combining topas, ISODISTORT and some python scripts you can automatically search through different space group possibilities for samples which undergo symmetry-lowering phase transitions.

Session 25 - Magnetic Refinements

Tutorial 39 - Topas v5 will perform magnetic Rietveld refinement. This tutorial takes you through three different ways of describing the low temperature magnetic structure of LaMnO3.

Session 25 - Stacking Fault Refinements

Tutorial 40 - Topas v6 lets you calculate the diffraction of materials with stacking faults. This tutorial takes you through this type of analysis using examples from the DIFFaX software package.

[Modified 16-Apr-2018 by John S.O. Evans. Pages checked for Google Chrome.]