Hydride ion as a two-electron donor in a nanoporous crystalline semiconductor 12CaO·7Al2O3

Katsuro Hayashi, Peter V. Sushko, Alexander L. Shluger, Masahiro Hirano, Hideo Hosono

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52 Citations (Scopus)


The 12CaO·7Al203 (C12A7) crystal with a nanoporous lattice framework exhibits high electrical conductivity with an activation energy of ∼ 1.5 eV when equilibrated in a hydrogen atmosphere above ∼800°C. The high conductivity is preserved in a quenched state below ∼600°C with a reduced activation energy of ∼0.8 eV, Such complex behavior in electrical conductivity is associated with incorporation of hydride ions (H-) in cages of the lattice framework. Electromotive force measurements reveal that the major carrier for the conductivity is electron with a small contribution by proton (H+), ruling out the possibility of direct intercage migration of the H- ion. A combination of these observations with the ab initio calculations leads to the conclusion that the electrons are thermally generated from the H- ion by the dissociation into two electrons and an proton, which is further converted to an OH- ion via reaction with an extraframework oxide ion (02-). The energy difference between the initial (H- + O2-) and the final (2e- + OH-) states as evaluated by the theoretical calculation is as small as ∼1 eV, which agrees well with an experimentally obtained enthalpy change, ∼1.4 eV. Thus, internal equilibration between the extraframework hydrogen and the oxygen species is responsible for the thermal generation of the carrier electron. It is also suggested that the same conductive (2e- + OH-) state is reached by the photoirradiation of H--containing C12A7. In this case the photoionization of H- forms an electron and an H o atom, which then forms an OH- ion and another electron with thermal assistance. The persistence of photoinduced conductivity is explained by the slow kinetics of the reverse process at room temperature.

Original languageEnglish
Pages (from-to)23836-23842
Number of pages7
JournalJournal of Physical Chemistry B
Issue number50
Publication statusPublished - Dec 22 2005
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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