Christian Schmidt (hokie@gfz-potsdam.de) and Martin A. Ziemann (marti@gfz-potsdam.de)

GeoForschungsZentrum Potsdam, Telegrafenberg D329, Potsdam 14473, Germany

Comparison of spectroscopic pressure sensors for hydrothermal diamond-anvil cell experiments

The difficulty to determine the pressure accurately is perhaps the main limitation in the application of diamond-and cells in hydrothermal studies. A number of techniques for determining the pressure in these cells have been developed in the past.
In this study, some spectroscopic pressure sensors were tested against each other at simultaneously elevated pressures and temperatures.

Water (which served as the pressure medium), quartz, ruby, and Sm-doped YAG were placed in a hydrothermal
diamond-anvil cell. Spectra of the three solids were recorded at pressures less than 20 kbar and temperatures between
23°C and 405 °C using a Dilor XY Raman microprobe. The temperature-corrected frequency shifts of the R1 ruby and
the Y1 Sm:YAG fluorescence lines and the 206 and 464 cm^-1 Raman lines of quartz were used to calculate pressures.

The data obtained so far show the expected good agreement between these techniques at low temperatures (to 75 °C).
At higher temperatures (above about 200 °C), only the frequency shift of 464 cm^-1 Raman line of quartz could be determined
with an accuracy required to derive reliable pressure values. This is due to the rapid increase in linewidth of the other lines
with temperature and the insufficiently known nonlinear temperature dependence of the frequency shift of the 206 cm^-1
Raman mode of quartz as a function of pressure.