Transparent insulating oxide 12CaO·7Al
2O
3 (C12A7) is converted into electronic conductor by replacing the oxygen ions in the crystallographic cages with electrons. At the low electron concentration (
Ne) <-10
20 cm
-3, C12A7 exhibits semiconductive properties due to hopping of localized electron. With increase of
Ne, it becomes metallic state at a critical
Ne-1×10
21 cm
-3. Fully oxygen-replaced C12A7 (C12A7:
e-) may be regarded as a room-temperature-stable electride in which electrons serve as anions. Small work function of 2.4 eV comparable to that in metal potassium is a characteristic of C 12A7:
e- and makes it a promising candidate for electron emitting source.
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