Powder Diffraction and Rietveld Tutorials



Powder Diffraction and Rietveld School April 2014 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 z:\licence\rietveld\rietveld_setup.bat there will be a shortcut to this on your desktop. Lecture notes and other useful files will belinked here. 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 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 13. 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. 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 Xray and neutron data. Also discusses structure solution from Xray 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 as 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 2theta 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 zmatrix description of local bodies to constrain internal symmetry. Data recorded on id31. Session 22  Neutron and Xray Combined Refinement How to perform a combined refinement using neutron and Xray data. Tutorial 17  Combined Refinement: Builds from earlier tutorial on ZrW2O8 and shows how to simultaneously fit Xray and neutron data. Also discusses structure solution from Xray 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. GSAS and Fullprof, for example, handle magnetic refinements which currently can't be done in topas. The packages come with many of their own builtin 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 Fullprof 1  Y2O3 lab data in fullprof Session 24  Spot the Errors These tutorials are designed to teach you how to troubleshoot 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 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 symmetrymode amplitudes rather than traditional atomic xyz coordinates of a distorted superstructure. Example based on simulated lab xray diffraction data from lowtemperature orthorhombic LaMnO3. The symmetry modes are obtained using the ISODISTORT software. Tutorial 37  Structural transformations. Directly refine symmetrymode amplitudes rather than traditional atomic xyz coordinates of a distorted superstructure. Example based on laboratory xray diffraction data from roomtemperature monoclinic WO3. The symmetry modes are obtained using the ISODISTORT software. Tutorial 38  Structural transformations. A more advanced symmetrymode refinement example based on roomtemperature WO3. Fit both neutron and Xray data. Try to determine spacegroup symmetry at high temperature using ISODISTORT. 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.


Modified 29Mar2014 by John S.O. Evans. 
