A review of the colossal permittivity of electronic conductors, specifically metals and carbons

The colossal permittivity of electronic conductors (specifically metals and carbons) is reviewed. Relative permittivity (even 10⁸) was predicted theoretically by Jonscher in 1999. The measured values that emerged in 2019 are up to 10⁶. The colossal permittivity is attributed to (i) charge-carrier polarization, and (ii) space charge polarization associated with the carrier-atom interaction at heterogeneities. Due to this interaction, the permittivity is more sensitive to the microstructure than the resistivity is, being increased by grain size reduction or cold work. The fraction of carriers that participate in the interaction under alternating current is low (up to 10⁻⁹ for graphite) and even lower (10⁻¹⁶) under direct current. The fraction is higher for carbons than metals. Ferroelectric behavior was not observed in the carbons, but in tin-silver (Sn-4Ag, a metal). The colossal permittivity of electronic conductors is consistent with the dominance of the absorption loss over reflection loss in the radio-wave regime.