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Photo-Induced Insulator-Semiconductor Transition in 12CaO·7Al2O3 (C12A7)

Published online by Cambridge University Press:  11 February 2011

Katsuro Hayashi
Affiliation:
Transparent Electro-Active Materials Project, Japan Science and Technology Corporation, KSP C-1232, 3–2–1 Sakado, Tatatsu-ku, Kawasaki 213–0012, Japan.
Satoru Matsuishi
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226–8503, Japan.
Toshio Kamiya
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226–8503, Japan.
Masahiro Hirano
Affiliation:
Transparent Electro-Active Materials Project, Japan Science and Technology Corporation, KSP C-1232, 3–2–1 Sakado, Tatatsu-ku, Kawasaki 213–0012, Japan.
Hideo Hosono
Affiliation:
Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226–8503, Japan.
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Abstract

We report the first electronic conduction in main group metal oxides (MGOs) or light-metal oxides, which are represented by alkaline-earth oxides, alumina, and silica. They are believed to be never converted to an electronic conductor. One of the MGOs, 12CaO·7Al2O3 (C12A7), has optical transparency, but electrical insulation limits intrinsic form. It is characterized by sub-nanometer sized cages in the lattice framework. Hydride ion, H- was incorporated into the cage by a thermal treatment of C12A7 single crystals or ceramics in hydrogen atmosphere. The product, C12A7:H, was colorless, transparent and a good insulator having electronic conductivity less than 10-10 S·cm-1. We found that the C12A7:H exhibits a coloration of yellowish green corresponding to optical absorptions at 2.8 and 0.4 eV with simultaneous conversion into an electronic conductor with 0.3 S·cm-1 at 300 K upon a irradiation of ultraviolet light. The conductive state continued even after the irradiation was stopped. Inversion to the insulator occurred when heated more than ∼320°C accompanying with rapid decay of the optical absorptions. When temperature rose above 550°C, H2 gas was released from the sample and the photosensitivity was lost. We consider that high concentration of F+-like centers are created by photo-released electrons from the H- anions being captured by empty cages. Further, a migration of the electrons at the F+-like centers may be responsible for the conduction. The visible light absorption loss is estimated to be only 1% for a 200 nm thick conductive C12A7:H films. The present properties provides novel applications such as direct optical writing of conducting wires on insulating transparent media.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

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