Energetics of formation and oxidation of microporous calcium aluminates: A new class of electrides and ionic conductors

Olga Trofymluk, Yoshitake Toda, Hideo Hosono, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

Microporous calcium aluminates with a common formula [Ca 12Al 14O 33-δ] 2δ+(2δ e -), (0 < δ≤ 1), represent a new family of electrides with conducting extraframework electrons encaged within the framework. Their enthalpies of oxidation to eliminate these electrons and obtain a stoichiometric Ca 12Al 14O 33 compound, and formation enthalpies relative to the most stable annealed calcium aluminate Ca 12Al 14O 33.46 (which contains excess oxygen probably as O - and O 2 - species), are studied by transposed temperature drop calorimetry and drop solution calorimetry in molten lead borate at 1080 K. The standard enthalpy of oxidation per O 2 consumed is -579.4±9.4 kJ/mol (or -144.8±9.4 kJ per encaged electron). The enthalpies obtained for samples with variable amounts of electrons (and less than 33 oxygens per formula unit) are compared to that for oxidation of a stoichiometric Ca 12Al 14O 33 sample to an oxygenrich composition. The study supports the idea that the oxidation of the stoichiometric Ca 12Al 14O 33 sample results in formation of extraframework ions (O 2 - and O -) with a standard enthalpy at 298 K of - 161.9 ± 11.2 kJ per mol of O 2, which is in good agreement with previous data by Hayashi et al. (J. Phys. Chem. B 2004, 108 (26), 8920) obtained for the same reaction at 898 K by electron paramagnetic resonance. The energetics of oxidation of electron-rich samples are discussed in terms of an electride model and "ionic" bonding of an encaged electron in the framework.

Original languageEnglish (US)
Pages (from-to)5574-5579
Number of pages6
JournalChemistry of Materials
Volume17
Issue number22
DOIs
StatePublished - Nov 1 2005
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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