Diffraction practical: Particle size broadening

Experiment

1. Take a coarse diffractogram (20^o to 80 in 0.1^o steps) of the corundum calibration standard. Locate the major Bragg peaks.
2. Take detailed diffractograms (about 4^o wide, 0.02^o step widh) of a few major peaks, spread over the whole angular range. This will be your measure of instrumental broadening.
3. Take coarse diffractograms of three samples:
   • nano-alumina from Nanophase
   • nano-alumina from our own production
   • partially sintered refractory analogue, "A50Z50"
4. Home in about three major Bragg peaks (avoid ones that overlap badly) in each sample and take detailed diffractograms of each of them.

Report

1. Measure the FWHM (full width at half magnitude) of each of the Bragg peaks in the detailed diffractograms. If peaks overlap, you will need to fit the combined peaks with a sum of Gaussians plus linear background.
2. From the corundum standard, work out an angle dependent instrument broadening by linear regression.
3. Work out the particle size by using the Scherrer formula. Remember to correct for the instrumental broadening. Leave the shape factor k=1.
4. Is the apparent particle size dependent on crystal orientation? If so, why?
5. Explain the broad background around 20-40^o in some of the samples.

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