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Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor


Materials that are good electrical conductors are not in general optically transparent, yet a combination of high conductivity and transparency is desirable for many emerging opto-electronic applications1,2,3,4,5,6. To this end, various transparent oxides composed of transition or post-transition metals (such as indium tin oxide) are rendered electrically conducting by ion doping1,2,3,4,5,6. But such an approach does not work for the abundant transparent oxides of the main-group metals. Here we demonstrate a process by which the transparent insulating oxide 12CaO·7Al2O3 (refs 7–13) can be converted into an electrical conductor. H- ions are incorporated into the subnanometre-sized cages of the oxide by a thermal treatment in a hydrogen atmosphere; subsequent irradiation of the material with ultraviolet light results in a conductive state that persists after irradiation ceases. The photo-activated material exhibits moderate electrical conductivity (0.3 S cm-1) at room temperature, with visible light absorption losses of only one per cent for 200-nm-thick films. We suggest that this concept can be applied to other main-group metal oxides, for the direct optical writing of conducting wires in insulating transparent media and the formation of a high-density optical memory.

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Figure 1: Incorporation of H- ions in C12A7.
Figure 2: Insulator–conductor conversion of C12A7:H.
Figure 3: Electronic conduction in C12A7:H.
Figure 4: F+ centre in C12A7:H.


  1. Ginley, D. S. & Bright, C. Transparent conducting oxides. MRS Bull. 25, 15–21 (2000)

    Article  CAS  Google Scholar 

  2. Hamberg, I. & Granqvist, C. G. Evaporated Sn-doped In2O3 films: Basic optical properties and applications to energy-efficient windows. J. Appl. Phys. 60, R123–R160 (1986)

    Article  ADS  CAS  Google Scholar 

  3. Robertson, J. Electronic structure of SnO2, GeO2, PbO2, TeO2 and MgF2 . J. Phys. C 12, 4767–4776 (1979)

    Article  ADS  CAS  Google Scholar 

  4. Kawazoe, H. et al. P-type electrical conduction in transparent thin films of CuAlO2 . Nature 389, 939–942 (1997)

    Article  ADS  CAS  Google Scholar 

  5. Kawazoe, H., Yanagi, H., Ueda, K. & Hosono, H. Transparent p-type conducting oxides: Design and fabrication of p-n heterojunctions. MRS Bull. 25, 28–37 (2000)

    Article  CAS  Google Scholar 

  6. Thomas, G. Invisible circuit. Nature 389, 907–908 (1997)

    Article  ADS  CAS  Google Scholar 

  7. Bartl, H. & Scheller, T. Zur Struktur des 12CaO·7Al2O3 . N. Jb. Miner. Mh. 35, 547–552 (1970)

    Google Scholar 

  8. Imlach, J. A., Glasser, L. S. D. & Glasser, F. P. Excess oxygen and the stability of “12CaO·7Al2O3”. Cement Conc. Res. 1, 57–61 (1971)

    Article  CAS  Google Scholar 

  9. Jeevaratnam, J., Glasser, F. P. & Glasser, L. S. D. Anion substitution and structure of 12CaO·7Al2O3 . J. Am. Ceram. Soc. 47, 105–106 (1964)

    Article  CAS  Google Scholar 

  10. Hosono, H. & Abe, Y. Occurrence of superoxide radical ion in crystalline 12CaO·7Al2O3 prepared via solid-state reaction. Inorg. Chem. 26, 1192–1195 (1987)

    Article  CAS  Google Scholar 

  11. Hayashi, K., Hirano, M., Matsuishi, S. & Hosono, H. Microporous crystal 12CaO·7Al2O3 encaging abundant O- radicals. J. Am. Chem. Soc. 124, 738–739 (2002)

    Article  CAS  Google Scholar 

  12. Watauchi, S., Tanaka, I., Hayashi, K., Hirano, M. & Hosono, H. Crystal growth of Ca12Al14O33 by the floating zone method. J. Cryst. Growth 237, 496–502 (2002)

    ADS  Google Scholar 

  13. Li, Q.-X. et al. Absolute emission current density of O- from 12CaO·7Al2O3 . Appl. Phys. Lett. 80, 4259–4261 (2002)

    Article  ADS  CAS  Google Scholar 

  14. Henderson, B. & Wertz, J. E. Defects in the alkaline earth oxides. Adv. Phys. 17, 749–855 (1968)

    Article  ADS  CAS  Google Scholar 

  15. Agullo-Lopez, F., Catlow, C. R. A. & Townsend, P. D. Point Defects in Materials Ch. 5 (Academic, London, 1988)

    Google Scholar 

  16. Williams, R. T. & Friebele, E. J. CRC Handbook of Laser Science and Technology (ed. Weber, M. J.) Part I Vol. III (CRC, Boca Raton, FL, 1986)

    Google Scholar 

  17. Hosono, H., Asada, N. & Abe, Y. Properties and mechanism of photochromism in reduced calcium aluminate glasses. J. Appl. Phys. 67, 2840–2847 (1990)

    Article  ADS  CAS  Google Scholar 

  18. Giamello, E., Paganini, M. C., Murphy, D. M., Ferrari, A. M. & Pacchioni, G. A. Combined EPR and quantum chemical approach to the structure of surface FS+(H) centres on MgO. J. Phys. Chem. 101, 971–982 (1997)

    Article  CAS  Google Scholar 

  19. Oliver, D., Hofmann, P. & Knözinger, E. H2 chemisorption and consecutive uv stimulated surface reactions on nanostructured MgO. Phys. Chem. Chem. Phys. 1, 713–721 (1999)

    Article  Google Scholar 

  20. Hayward, M. A. et al. The hydride anion in an extended transition metal oxide array: LaSrCoO3H0.7 . Science 295, 1882–1884 (2002)

    Article  ADS  CAS  Google Scholar 

  21. Mott, N. F. & Davis, E. A. Electronic Processes in Non-crystalline Materials, 2nd edn (Oxford Univ. Press, Oxford, 1979)

    Google Scholar 

  22. Weil, J. A., Bolton, J. R. & Wertz, J. E. Electron Paramagnetic Resonance (Wiley, 1994)

    Google Scholar 

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We thank I. Tanaka and S. Watauchi for growing the single crystals, S. Takeda for NMR measurements, and M. Sadakata, Q.-X. Li and T. Nishioka for TOF-MS measurements.

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Correspondence to Katsuro Hayashi.

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Hayashi, K., Matsuishi, S., Kamiya, T. et al. Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor. Nature 419, 462–465 (2002).

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