Diffraction practical: Thermal expansion

Experiment

1. Place a 2p copper coin on a few layers of paper or some cardboard (for thermal insulation) and place it on the diffractometer turntable. Take a coarse diffractogram (40^o to 75 in 0.1^o steps). You should see three Bragg peaks.
2. Take a detailed diffractogram of each peak (about 5^o wide, 0.02^o step widh).
3. Take away and replace the coin and take another coarse diffractogram of one of the peaks a few times to judge the error resulting from repositioning the coin.
4. Fix the thermocouple to the turntable.
5. Heat the coin as much as possible, using the hot plate provided. Transfer it carefully to the turntable.
6. Collect data at 0.02^o resolution on each of the three peaks in turn while noting the change of temperature at the start of each diffractogram.

Report

1. Is the position of the Bragg peaks sensitive to the height of the surface of the coin? If so why?
2. Work out the linear thermal expansion coefficients along the crystallographic orientations probed by the three Bragg peaks. You may need to look up Bragg's law...
3. Can you work out the volume expansion coefficient?
4. Compare your results with literature data.
5. Sketch the unit cell of copper at room temperature and at the highest temperature used in the experiment.

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