Elasticity of single-crystal quartz to 10 GPa

Abstract

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 pres- sure trends. A decrease in the magnitudes of C14 and C66 with pressure is observed, while C 44 shows a weak pressure dependence. Our measured elastic constants are more con- sistent 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 adia- batic bulk modulus, K 0S ʹ, and shear modulus, G 0 ʹ, of α-quartz of 6.2(2) and 0.9(1), respectively. The equation of state obtained from our data is consistent with static X-ray diffrac- tion data. A finite-strain extrapolation of our data predicts a violation of a Born stability criterion, indicating a mechani- cal 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.