What happens to many substances under pressures greater than one million bars?

Under pressures exceeding one million bars, matter undergoes significant physical and structural transformations as atoms are forced closer together, reducing volume and shortening interatomic distances.12

Key effects include:

• Structural Phase Transitions: Materials often undergo transitions to denser, more closely packed atomic arrangements. For example, ionic compounds like rock-forming minerals may rearrange their structures to increase the coordination number of atoms.1
• Metallization: It is predicted that all matter will ultimately become metallic at sufficiently high pressures due to the forced overlap of electron orbitals, which induces electron delocalization. This transition from insulator to metal has been observed in various elements—including silicon, germanium, and hydrogen—as well as in numerous chemical compounds.1
• Property Changes: These extreme conditions induce dramatic changes in physical properties, such as electric conductivity, thermal conductivity, and viscosity. While some materials exhibit smoothly varying trends, others display sharp, reproducible discontinuities in volume and electric resistance, signaling phase transitions.2

These phenomena are essential for understanding the composition and behavior of materials within the deep interiors of the Earth and other planets.3