DEVIATORIC STRESS IN A QUASI-HYDROSTATIC DIAMOND-ANVIL CELL - EFFECT ON THE VOLUME-BASED PRESSURE CALIBRATION

The deviatoric stress in gold as a function of pressure and temperature, in a diamond anvil cell with neon as the pressure medium, is measured based on gold diffraction peaks. We find that the deviatoric stress becomes detectable at a pressure of about 15 GPa and reaches 0.62 GPa by 30 GPa. Upon heating, the deviatoric stress decreases rapidly and disappears at a temperature of about 650 K. The effect of deviatoric stress on the unit cell volume measurement and further on the volume-based pressure calibration is directly proportional to K/mu of the measured material, and it is also related to the anisotropy, as well as the sip of die deviatoric stress and the orientation of the x-ray diffraction. We find that the measured unit cell volume of gold is very sensitive to the deviatoric stress due to a high value of K/mu. Although the observed deviatoric stress may be insignificant for most samples, it causes a significant systematic error on die pressure calibration based on the unit cell volume of gold.