Hydrostaticity in high pressure experiments: some general observations and guidelines for high pressure experimenters

ABSTRACT The characteristics of hydrostatic stress conditions are discussed and compared with real experimental observations made under high pressure with a diamond-anvil cell. While fluid pressure-transmitting media give a well-defined single stress condition, solid pressure-transmitting media give a variety of stress conditions within the limit of their shear strength under high pressure. Owing to its low shear strength, solid helium would be the best choice for a pressure-transmitting medium to at least 100 GPa. However, helium is so compressible that care should be taken on minimizing irregular deformation of a gasket hole, which often causes complicated stress states. A review is given on the quasi-hydrostatic limits of solidified pressure-transmitting media, and some ways to reduce nonhydrostaticity are discussed including the case of low-temperature experiments.