Materials Under Extreme Conditions and Implications for Earth and Planetary Science

In chemistry under extreme conditions, shock compression forces to alter the chemical bonds by densification. A density increase does not always reduce the bond distance between atoms and often increases it due to an increase in the coordination number. In silicates, the connections among SiO4 tetrahedra with point-, edge-, and face-sharing affect the density increase by compression as well as the coordination changes associated with the shearing of the SiO6 octahedra at high pressures. These changes occur not only in crystals but also in amorphous states. The nature of the chemical bonds also alters at extreme states. The shock compression technique is currently the only way to generate the conditions at the center of the Earth’s core and the interior conditions of large planets, including Super-Earths. One of the most challenging subjects regarding the Earth’s core is the boundary condition between the liquid outer core and solid inner core. It is crucial to determine the core temperature profile based on the boundary condition, although it is affected by the amount and kind of coexisting additional light elements. Pressures within the mantles and cores of large planets are over 500 GPa, and the interior materials consist of low Z materials, silicates, carbides, and iron-nickel alloys. Their stabilities and properties under planetary interior conditions are important to model and understand their interiors and cores as the most likely candidates. There are several experimental data available for the potential materials. This chapter summarizes the recent data.