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

Abstract

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 °C. Changes in the Raman shift of the 128-cm⁻¹ band with Ps and Ts are 9–16 cm⁻¹/GPa and ~ (50–40) × 10⁻³ cm⁻¹/°C, respectively, at 200–700 °C and < 1.0 GPa; the corresponding values for the 464-cm⁻¹ band are ~9 cm⁻¹/GPa and ~14 × 10⁻³ cm⁻¹/°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 °C (∆ω₁₂₈) were fitted into an equation to express their relation:

∆ω₁₂₈ (cm⁻¹) = 1.20176 × 10⁻¹⁰ × T⁴–1.64508 × 10⁻⁷ × T³ + 2.0665 × 10⁻⁵ × T²–0.02134 × T + 0.00599 × P + 1.60394 × 10⁻⁵ × T × P + 0.48515,

where 23 ≤ T (°C) ≤ 700, P (MPa) < 1000, and R² = 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 ∆ω₁₂₈ is obtained in high P–T experiments using HDAC or other types of optical cells.