Anomalous Phase Diagram and Conformational Behaviors of n-Hexane at High Temperatures and High Pressures

n-Hexane has been widely used in the fields of chemistry and energy sources, as well as in studies of ultrafast dynamics of quantum dots at high pressures/temperatures. Here, we report the solid–liquid phase diagrams of n-hexane from room temperature to 651 K within 10 GPa by using in situ Raman spectroscopy and microscopic photography techniques. An anomalous melting phenomenon has been observed in n-hexane, that is, the solid–liquid phase transition critical point at the same pressure is different in the processes of heating and cooling, and there is a great relaxation process. This may be attributed to that the temperature and pressure can affect the equilibrium of the internal conformation of n-hexane. As the pressure increases, the relaxation effect will gradually increase. In addition, the internal conformational database of n-hexane under control of temperature and pressure was obtained through Raman results.