Improving pressure and temperature metrology in laser-heated diamond anvil cell experiments: a new perspective on KCl as a pressure marker

The laser-heated diamond anvil cell is widely used for experiments under extreme conditions, though pressure and temperature measurements often remain sources of error and inconsistency across studies. This work emphasizes the importance of accurately measuring the temperature distribution across the sample using an enhanced laser-heating setup and a four-color pyrometry system. Pressure calibration was improved by developing a dedicated protocol based on X-ray diffraction measurements of recrystallizing KCl in contact with the sample, bringing pressure and temperature readings closer to the actual sample conditions. When recrystallized KCl is not visible in diffraction patterns, we propose a thermal-pressure correction based on finite element simulations and validated against KCl metrology, which provides greater accuracy than previous methods. As a case study, the methodology was applied to determine the melting curves of Fe-FeO iron-wüstite and FeO wüstite.