Metallization pressure

Metallization pressure is the pressure at which an insulating or semiconducting material becomes metallic, typically because compression changes its electronic structure.

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Electronic band structure: The allowed electron energy states in a solid, organized by energy and crystal momentum. Pressure can shift and broaden bands until occupied and empty states overlap.
Hydrogen: The lightest chemical element, which forms molecular and atomic phases under different conditions. Its predicted transition to metallic states at extreme pressure remains a major experimental challenge.
Diamond anvil cell: A device that compresses tiny samples between opposing diamond tips to reach very high pressures. It makes laboratory measurements near predicted metallization pressures possible.
Electrical conductivity: A measure of a material’s ability to carry electric current. Conductivity thresholds help distinguish a true metallic state from a merely narrowed-gap semiconductor.
Band gap: The energy range separating a solid’s valence-band states from its conduction-band states. Closing this gap is one route by which compression produces metallic conduction.
Oxygen: A chemical element that is a diatomic gas at ordinary conditions and has multiple solid phases under pressure. Compressed solid oxygen becomes metallic in a high-pressure phase.
Shock compression: A method of producing extreme pressure and temperature by sending a shock wave through a material. It probes transient metallization in materials that are difficult to compress statically.
Optical reflectivity: The fraction of incident light reflected by a material at specified wavelengths and conditions. Reflectivity can reveal free-carrier behavior when direct electrical contacts are impractical.
Mott transition: A transition between insulating and metallic behavior driven by changes in electron correlation relative to electron mobility. Some pressure-driven insulator-to-metal transitions arise when compression weakens correlation effects.
Iodine: A halogen element that forms a molecular solid at ordinary pressure. Compression drives iodine from molecular insulating behavior toward metallic conduction.