Fundamental infrared absorption features of α-quartz: An unpolarized single-crystal absorption infrared spectroscopic study

With an unpolarized light normally directed to three alpha-quartz crystal plates cut perpendicularly (Z-cut) or parallel to the optical axis (X-cut and Y-cut), single-crystal absorption infrared spectra from similar to 1300 to 50 cm(-1) were measured. To obtain optimal results, thin sections with different thicknesses (similar to 100, 50, 20 and 6 mu m) were prepared and probed. On the basis of symmetry analysis and pertinent knowledge in the literature, the effect of possible interference in the absorbance spectra was evaluated and tentatively removed, and optimal spectroscopic results (peak position, peak intensity, and peak width) were obtained for the fundamental IR-active modes of alpha-quartz, including all four A(2) modes and seven E modes. In particular, the present contribution directly observed those extremely strong light-absorbing IR peaks in the similar to 1300-1000 cm(-1) region, which had not been experimentally detected before. Supplementary Raman data were collected from these well-polished crystal plates. Our exercise eventually led to a full description of the vibrational features of alpha-quartz. The full characterization of the vibrational properties of alpha-quartz should shed lights on better understanding of the structural and vibrational features of alpha-quartz, its polymorphs, vitreous silica, and even other silicate minerals.