A density functional study of vacancy formation in grain boundaries of undoped α-alumina

Takafumi Ogawa, Akihide Kuwabara, Craig A.J. Fisher, Hiroki Moriwake, Katsuyuki Matsunaga, Kenji Tsuruta, Satoshi Kitaoka

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15 Citations (Scopus)

Abstract

Recent oxygen permeation experiments with α-alumina have shown that the two major diffusing species at the grain boundaries, i.e. oxygen and aluminum vacancies, switch over in terms of their dominance depending on the oxygen partial pressure at high temperatures (the so-called p-n transition). In order to investigate this transition behavior the formation energies of charged oxygen and aluminum vacancies at Al2O3 grain boundaries were evaluated using density functional theory. The electronic structures affecting the carrier concentrations are assessed for three types of grain boundaries. The ratios of the grain boundary band gaps relative to the bulk value lie in the range of 0.6-0.85 depending on the degree of grain boundary misorientation. From the formation energies we find that, at band gaps around 60% compared to the bulk value, the dominant vacancy alters depending on the pressure, consistent with the oxygen permeation experiments. Our results suggest that the band bap narrowing occurring at grain boundaries enhances the creation of oxygen vacancies and conduction electrons, facilitating the observed transition.

Original languageEnglish
Pages (from-to)365-371
Number of pages7
JournalActa Materialia
Volume69
DOIs
Publication statusPublished - May 2014

Keywords

  • Alumina
  • Density functional theory
  • Grain-boundary diffusion
  • Oxygen permeation
  • Vacancies

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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    Ogawa, T., Kuwabara, A., Fisher, C. A. J., Moriwake, H., Matsunaga, K., Tsuruta, K., & Kitaoka, S. (2014). A density functional study of vacancy formation in grain boundaries of undoped α-alumina. Acta Materialia, 69, 365-371. https://doi.org/10.1016/j.actamat.2014.01.059