Electron Carrier Generation in a Refractory Oxide 12CaO·7Al 2 O 3 by Heating in Reducing Atmosphere: Conversion from an Insulator to a Persistent Conductor

Electron carriers were generated in refractory oxide 12CaO·7Al 2 O 3 (C12A7) through a thermal treatment in a reducing CO/CO 2 atmosphere, and the reduction process was thermodynamically analyzed. Electrical‐conductive C12A7, which had an electron concentration of ∼8 × 10 19 cm −3 and an electrical conductivity of ∼4 S/cm at 300 K, was obtained by extracting free O 2− ions in sub‐nanometer‐sized cages in the C12A7 lattice and leaving electrons behind. The enthalpy for this substitutive reaction is +425 kJ/mol, suggesting that stoichiometric C12A7 is more stable in air than the C12A7 electride.