Submitted by Maggie Geselbracht / Reed College on Fri, 02/22/2008 - 19:01
My Notes
Categories
Prerequisites
General Chemistry
Course Level
Second year
Topics Covered
Diffraction
Physical methods / analytical techniques
Subdiscipline
Solid State and Materials Chemistry
Description
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.  
Attachment Size
Lab handout for the students 253 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)

Related activities
Determining Molecular Structure: An Experimental Simulation of X-ray Diffraction
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
Web Resources
Link to download free UnitCell software
Link to resource on Miller Indices
Evaluation
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
Attribution, Non-Commercial, Share Alike CC BY-NC-SA