22 Feb 2008

Introduction to Powder X-ray Diffraction

Lab Experiment

Submitted by Maggie Geselbracht, Reed College
This quick lab experiment is designed to introduce students to powder X-ray diffraction including sample preparation, data collection, and the analysis of diffraction data to refine lattice parameters.  Diffraction data is collected for a sample of the cubic perovskite SrTiO3 (useful data can be obtained in relatively short times) and compared to data collected previously (over 6 hours) for the orthorhombic perovskite CaTiO3.  Students index the diffraction pattern of SrTiO3 by comparison to  the JCPDS database, and use a free program, UnitCell, to refine the lattice parameter.  
Microsoft Office document icon Lab handout for the students253 KB
Learning Goals: 

A student should acquire hands-on experience:

  • Preparing samples for X-ray powder diffraction
  • Using the X-ray powder diffractometer to set-up and acquire diffraction data
  • Analyzing the raw diffraction data by applying the background subtraction and K-alpha 2 stripping algorithms, and running the peak-picking software
  • Indexing their diffraction pattern by comparison to a known pattern and refining the lattice parameters of their sample 
In addition, by comparing the diffraction patterns of SrTiO3 and CaTiO3, a student should be able to explain the effect of lowering the crystal symmetry (from cubic to orthorhombic) on the diffraction pattern.
Equipment needs: 

X-ray powder diffractometer

Sample of SrTiO3 (can be purchased or made by firing SrCO3 and TiO2 at temperatures > 1000˚C)

Implementation Notes: 
This lab experiment typically follows the Optical Transform experiment simulating X-ray diffraction and introduces students to the powder diffractometer, data collection and analysis, and the UnitCell program, which may be used in a subsequent experiment.  The UnitCell program can be somewhat buggy, particularly the PC version.  But it is a very helpful (and free!) program.
Time Required: 
1 hour lab time, 1 hour for analysis
Evaluation Methods: 
Typically, students complete the analysis in their lab notebooks and their answers to the discussion questions in the lab handout are assessed.
Evaluation Results: 
This lab is mostly about learning how to run the diffractometer and analyze data.  Most students acquire these skills with minimal difficulty.  If they do not, then we learn that pretty quickly in follow-up weeks when they are expected to collect powder diffraction data on their own as "experienced users."
Creative Commons License: 
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