Advanced Certificate in Powder Diffraction on the Web Chapter 23 School of Crystallography, Birkbeck College, University of London

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Aims & Objectives

The aim of this chapter is to provide you with the necessary information to produce, and interpret, reports on the results of crystallographic work using the technique of powder diffraction and analysis by Rietveld refinement. The class of report focussed on is an article for a scientific journal, but the production and deciphering of Crystallographic Information Files (CIF) is also discussed. The purpose and usage of structural databases is described, as these have many uses, particularly in the production of articles. Many aspects of the material you have covered in this course will be touched upon in this section and it may be necesssary for you to review certain sections as you proceed.

More specific objectives are given below:

• You will learn about the necessary sections that need to be included in an article and what to look for in other peoples articles under these same sections. Details of the information you should provide on the experimental details, including sample preparation and data collection, on structural model determination and the Rietveld refinement itself are covered, as well as what should be reported in the results of the refinement and the derived geometric parameters. The final important section of article preparation covered is how to describe the structure, with necessary graphics, and to compare the structure you are reporting with others found in the literature. The points you should consider when interpreting and assessing other peoples work are emphasised in each section.
• You will learn about powder Crystallographic Information Files (CIF), what they are, the general terms used in their production, and examples of these terms put into practice in various sections of a CIF.
• The uses of structural databases will be presented to you along with very general searching strategies you might want to use to search the databases. The main databases you might need to use are described, and an example of the data you can retrieve and type of analysis that can be done for one of the databases is presented.

After completing this chapter you should be able to:

• Produce a full journal article describing the Rietveld refinement of a polycrystalline material;
• Understand what is being discussed in other articles reporting the Rietveld refinement of a polycrystalline material and be able to assesss the quality of the work that is being reported;
• Describe what a powder CIF is, understand its format and be able to produce certain sections of a CIF;
• Know when you need to refer to a structural database, and what searches you might use to extract the information;
• Identifiy the database you need for your particular research area and form an idea of the type of output that you would expect from an entry from any structural database.

If you have any questions, points requiring clarification or the like, please email your questions to the notice board.

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