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.