Fundamental lattice vibrations in quartz

The fundamental lattice vibrations in quartz (normal modes) were examined in an attempt to find better test methods to characterize impurities. A computer model of alpha quartz was constructed using the atomic positions in the quartz unit cell and a Keating-type interatomic potential. Using this model, the infrared (IR) absorption was calculated for the fundamental modes. This perfect (no defect) model was compared with experimental IR absorption results and with experimental data taken from the literature, and was found to be in qualitative agreement with both. Another model was also constructed which simulated an aluminum substantial defect by changing the mass of one of the three silicon atoms in the unit cell to the mass of aluminium. This represents an Al to Si concentration of 33%. The IR absorption results of the `defect´ model showed very little change in the absorption peaks. Even though this method was found to be impractical for aluminum detection, it did result in the construction of a relatively good numerical model for studying the fundamental atomic vibrations in quartz