Fig. 2
From: Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa
Representative Raman spectra of different pressure conditions. Raman spectra were obtained from SA1 (SiO2 + 3.9 mol% Al2O3) and SA2 (SiO2 + 20.5 mol% Al2O3), respectively. They were measured from reflected light of the incident laser beam three times (a1, a2, a3, b1, b2, b3). Their differential spectra dI∕dv are also shown (a4, a5, a6, b4, b5, b6). The high-frequency edge of the Raman band was defined as the minimum of the dI∕dv. The red lines represent the fitting curves using Gaussian functions to determine the minimum position. Numbers in parentheses represent uncertainties in the last digit for both wave number and pressure. Uncertainties for the wave number of the minimum position of dI∕dv in each spectrum were derived from the errors of the curve fitting. The total uncertainties for pressure were finally estimated from the standard deviation (1σ) of each determined pressure value at each point