Large conductivity enhancement in polycrystalline 12CaO · 7Al2O3 thin films induced by extrusion of clathrated O ions by hot Au implantation and ultraviolet light illumination

Large enhancement in electrical conductivity from <10^?10 S cm^?1 to 4 × 10^?2 S cm^?1 was achieved in polycrystalline 12CaO · 7Al₂O₃ (p-C12A7) thin films by hot Au⁺ implantation at 600 °C and subsequent ultraviolet (UV) light illumination. Although the as-implanted films were transparent and insulating, the subsequent UV-light illumination induced persistent electronic conduction and coloration. A good correlation was found between the concentration of photo-induced F⁺-like centers (a cage trapping an electron) and calculated displacements per atom, indicating that the hot Au⁺ implantation extruded free O^2? ions from the cages in the p-C12A7 films by kick-out effects and left electrons in the cages. These results suggest that H^? ions are formed by the Au⁺ implantation through the decomposition of preexisting OH^? ions. Subsequent UV-light illumination produced F⁺-like centers via photoionization of the H^? ions, which leads to the electronic conduction and coloration.