Abstract. The infrared spectra of natural quartz, and synthetic quartz produced in
conditions relevant to natural environments, generally contain some
association of OH-stretching absorption bands at 3596, 3585, 3483, 3431,
3379 and 3313 cm−1, and/or a broad band at ∼ 3400 cm−1. In this study, a series of OH-bearing defects has been
theoretically investigated from first principles within the density
functional theory framework. The optimized structure, infrared spectroscopic
properties and relative energy of defect configurations have been
determined. Comparison with experimental observations enables the
identification of atomic-scale configurations related to the
experimentally observed OH-stretching bands. Consistent with previous
interpretations, the results confirm the assignment of the bands at 3596 and
3483 cm−1 to OH defects associated with B3+ substituting for
Si4+ and to OH defects associated with Li+ cations located in the structural channels,
respectively. They also confirm the assignment of the bands at 3313 and 3379 cm−1 to OH associated with the Al3+-for-Si4+ substitution
and, by implication, the previously given interpretation of the 3431 cm−1 band in terms of Fermi resonance. The band at 3585 cm−1 does
not appear to be related to a hydrogarnet-type defect, as has been proposed
previously, but potentially corresponds to isolated OH− groups bridging
two Si atoms, where the charge compensation is ensured by a nonlocal
mechanism.
Variations of OH defects and chemical impurities in natural quartz within igneous bodies
