Elasticity of single-crystal quartz to 10 GPa

The second-order elastic constants of quartz were determined by Brillouin spectroscopy to 10 GPa in a diamond anvil cell. All elastic constants exhibit smooth pressure trends. A decrease in the magnitudes of C (14) and C (66) with pressure is observed, while C (44) shows a weak pressure dependence. Our measured elastic constants are more consistent with previous density functional theory calculations than with earlier experimental results. Aggregate elastic moduli were calculated and fit to a finite-strain equation of state, yielding values for the pressure derivatives of the adiabatic bulk modulus, K E-0S(1), and shear modulus, G E-0(1), of alpha-quartz of 6.2(2) and 0.9(1), respectively. The equation of state obtained from our data is consistent with static X-ray diffraction data. A finite-strain extrapolation of our data predicts a violation of a Born stability criterion, indicating a mechanical instability in the structure, at 26 GPa which is broadly consistent with the pressure range at which a phase transition and pressure-induced amorphization in quartz are observed.