Hydrostaticity of Pressure Media in Diamond Anvil Cells

Hydrostaticity under high pressure of several materials from solid, fluid to gas, which are widely used as pressure media in modern high-pressure experiments, is investigated in diamond anvil cells. Judging from the R-line widths and R₁-R₂ peak separation of Ruby fluorescence, the inert argon gas is hydrostatic up to about 30GPa. The behavior of silicon oil is found to be similar to argon at pressures less than 10GPa, while the widening of R-lines and increase of R₁-R₂ peak separation at higher pressure loads indicate a significant degradation of hydrostaticity. Therefore silicon oil is considered as a good pressure medium at pressures less than 10GPa but poor at higher pressures.