Towards jointin situdetermination of pressure and temperature in the large volume press exclusively from X-ray diffraction

Abstract

Since high-pressure devices have been used at synchrotron facilities, accurate determination of pressure and temperature in the sample has been a crucial objective, particularly for experiments that simulate the Earth's interior. However, in some cases using a thermocouple may have a high likelihood of failure or is incompatible with a high-pressure assembly. To address these challenges and similar issues, we aim to expand a previously proposed solution: to jointly estimate pressure and temperature (PT) throughin situX-ray diffraction, to cover a wider range of internalPTcalibrants tested over largerPTranges. A modifiable Python-based software is offered to quickly obtain results. To achieve these aims,in sitularge volume press experiments are performed on pellets of intimately mixed powders of a halide (NaCl, KCl, KBr, CsCl) or MgO and a metal (Pt, Re, Mo, W, Ni) in the pressure range 3–11 GPa and temperature range 300–1800 K. Although the pressure range was chosen for practical reasons, it also covers an equally important depth range in the Earth (down to 350 km) for geoscience studies. A thermocouple was used to validate thePTconditions in the cell assemblies. The key results show that choosing the appropriate calibrant materials and using a jointPTestimation can yield surprisingly small uncertainties (i.e.<±0.1 GPa and <±50 K). This development is expected to benefit current and future research at extreme conditions, as other materials with high compressibility or high thermal pressure, stable over largePTranges, may be discovered and used asPTcalibrants.