Diffraction practical: Phase identification

Experiment

1. Take diffractograms of the full pattern (5^o to 80^o in 0.1^o steps) of pure alpha and beta silicon nitride.
2. Compare the two pattern and decide which peaks are best suited to distinguish the two. These should be the strongest peaks available with little overlap between the two forms.
3. Prepare mixtures of the two alpha and beta phases of silicon nitride. Starting from a 50-50 mixture, work towards progressively purer beta-Si3N4, and work out how much of the beta-form you can identify with any certainty in a mixture. You should aim for five to six different mixing ratios. For each mixture, take detailed diffractograms around your chosen peaks (about 5^o wide, 0.02^o step widh); more patterns of the full angular range aren't needed.
4. If you have time left, extend the series towards pure alpha-Si3N4.

Report

1. Look up the crystal structures of the alpha and beta forms of silicon nitride and explain the differences between their diffraction patterns.
2. Explain which peaks you've chosen to determine the presence of the minority component, and why.
3. Integrate the peaks and determine whether the ratio of the peak areas of both components follows the mixing ratio.

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