Adiabat-reduced isotherms at 100GPa pressures

The method of deriving shock wave reduced isotherms (SWRIs) as pressure standards up to 150GPa in a diamond anvil cell (DAC) is discussed. This method is applicable to any adiabatic compression. Hugoniots and isentropes can both be used as reference curves in this analysis. While only Hugoniots have been used to date, isentropes will probably be used in future to develop standards above 200GPa. Accuracies of SWRIs of Al, Cu, Ta, W, Au, Mo, and Pt are discussed. Hugoniots of diamond and MgO are in excellent agreement with their respective isotherms measured in DAC up to 140 and 55GPa, respectively. The equation of state of a weakly compressible material is sensitive to pressure and weakly sensitive to temperature. Thus, strong crystals, such as diamond, MgO, and BN, can be used as pressure standards and temperature can be measured independently. Future experiments to improve accuracies of static-pressure standards are suggested.