Extending the single-crystal quartz pressure gauge up to hydro­static pressure of 19 GPa

In situ high-pressure diffraction experiments on single-crystal α-quartz under quasi-hydrostatic conditions up to 19 GPa were performed with diamond-anvil cells. Isotropic pressures were calibrated through the ruby-luminescence technique. A 4:1 methanol–ethanol mixture and the densified noble gases helium and neon were used as pressure media. The compression data revealed no significant influence of the pressure medium at room temperature on the high-pressure behavior of α-quartz. In order to describe its compressibility for use as a pressure standard, a fourth-order Birch–Murnaghan equation of state (EoS) with parameters K_T0 = 37.0 (3) GPa, K_T0′ = 6.7 (2) and K_T0′′ = −0.73 (8) GPa⁻¹ was applied to fit the data set of 99 individual data points. The fit of the axial compressibilities yields M_T0 = 104.5 (8) GPa, M_T0′ = 13.7 (4), M_T0′′ = −1.04 (11) GPa⁻¹ (a axis) and M_T0 = 141 (3) GPa, M_T0′ = 21 (2), M_T0′′ = 8.4 (6) GPa⁻¹ (c axis), confirming the previously reported anisotropy. Assuming an estimated standard deviation of 0.0001% in the quartz volume, an uncertainty of 0.013 GPa can be expected using the new set of EoS parameters to determine the pressure.