In-situ determination of the graphite-diamond transition at extreme temperature

The graphite-diamond transition is an important high-pressure phase transition because of its applications in geosciences, materials science, physics, and the diamond industry. Experiments on the phase transition have been limited to temperature below 2000 K. Here, we propose to precisely determine the graphite-diamond transition boundary at temperatures above 2000 K by in-situ X-ray diffraction measurements. We have developed an X-ray transparent boron-dopped diamond heater to achieve extreme temperature at high pressure. We will determine the transition boundary by detecting a resistance change of the heater, coupled with in-situ determination of pressure using the MgO pressure scale. The experimentally determined diamond-graphite boundary will represent the highest temperature-pressure achievable in large-volume press and fill the gap in the temperature range between 2000 K and the triple temperature. The result is expected to be extensively cited in multiple research disciplines.