Pressure sensor based on the Raman shift of the 128-cm-1 band of quartz for pressure measurements in hydrothermal diamond-anvil cells

To interpret data collected from high-pressure (P)-temperature (T) experiments simulating geological processes, pressure information during these experiments is crucial. Traditionally, the Raman shifts of the quartz 464-cm(-1) band are commonly used as a hydrostatic-pressure calibrant in such experiments, particularly in those performed using hydrothermal diamond-anvil cells (HDACs). In this study, we conducted experiments using HDAC and a Raman spectrometer to investigate the sensitivity of the quartz 128-cm(-1) Raman band to changes in P and T. We found that the Raman shift of this band exhibits higher sensitivity to changes in P and T than the 464-cm(-1) band at Ts above 200 degrees C. Changes in the Raman shift of the 128-cm(-1) band with Ps and Ts are 9-16 cm(-1)/GPa and similar to (50-40) x 10(-3) cm(-1)/degrees C, respectively, at 200-700 degrees C and < 1.0 GPa; the corresponding values for the 464-cm(-1) band are similar to 9 cm(-1)/GPa and similar to 14 x 10(-3) cm(-1)/degrees C, respectively. The experimental data of Ps, Ts, and the Raman shifts of the quartz 128 cm(-1) band relative to that at 0.1 MPa and 23 degrees C (Delta omega(128)) were fitted into an equation to express their relation: Delta omega(128) (cm(-1)) = 1.20176 x 10(-10) x T-4-1.64508 x 10(-7) x T-3 + 2.0665 x 10(-5) x T-2-0.02134 x T + 0.00599 x P + 1.60394 x 10(-5) x T x P + 0.48515, where 23 <= T (degrees C) <= 700, P (MPa) < 1000, and R-2 = 0.9986. Based on the scattered experimental data, the error of this equation is +/- 20 MPa. Based on this equation, the hydrostatic P can be calculated at a specific T when Delta omega(128) is obtained in high P-T experiments using HDAC or other types of optical cells.