2008 年 29 巻 1 号 p. 2-9
12CaO·Al2O3 (C12A7) crystal is a constituent of alumina cements and an electrical insulator with a large band gap of ∼7 eV. It is possible to replace almost all the O2− ions in its crystallographic cages with electrons by reduction treatments. As a result, C12A7 is converted to a metallic conductor C12A7:e− with a low work function of ∼2.4 eV via an insulator-metal transition. We have developed a technique to prepare C12A7:e− thin films. The electrical and optical properties, and also an application to an electron injection layer for an organic light emitting device are reviewed.