Grüneisen parameter as an important parameter in condensed matter has great significance for measuring thermodynamics, elasticity, and inelasticity of matter. In the study of properties of condensed matter at high temperature and high pressure, the Grüneisen parameter links the elastic and thermal properties, playing a crucial role in constructing the equation of state of matter and studying thermodynamics under high pressure. In the pressurization experiment, due to the slow pressurization rate, it is difficult to isolate the heat exchange between the sample and the surrounding environment. So, it is difficult to achieve the isentropic process needed by the direct measurement of Grüneisen parameters under high pressure, resulting in more reports on Guneisen parameters within the range of several tens of thousands of atmospheres. There are not any direct measurement experiments for Grüneisen parameters within a wider pressure range. Solving this problem is of great significance for studying thermal effects of matter under high pressure and the equation of state.

Recently, a research team, which was jointly formed by Nankai University, Center for High Pressure Science & Technology Advanced Research (HPSTAR) in Beijing, and Institute of Chemistry of the Chinese Academy of Sciences (corresponding authors: Su Lei, Dong Xiao and Yang Guoqiang), obtained the pressurization rate of several million atmospheres in milliseconds by using the self-designed dynamic diamond anvil cell (dDAC) and ultra-fast in-situ measurement system. Due to the time being very short, the heat exchange between the sample and the environment is small and negligible, leading to achieving quasi-isentropic compression of the sample and obtaining the Grüneisen parameters of the sample. The team chose the B1 phase of sodium chloride as the sample and measured its thermal effect during rapid loading, realizing Grüneisen parameter measurement of sodium chloride over a wide pressure range. This provides a new method for further studying the thermodynamics of matter. The research results with the title Expanding the Pressure Frontier in Grüneisen Parameter Measurement: Study of Sodium Chloride were published in the recent issue of Physical Review Letters, with Kong Jun, Shi Kaiyuan, and Dong Xingbang as the first co-authors, and Nankai University as the first authors affiliation.

（Edited and translated by Nankai News Team.)