Large conductivity enhancement in polycrystalline 12CaO · 7Al2O3 thin films induced by extrusion of clathrated O2− 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 O2− 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.