Effect of an internal electric field on the redox energies of ALn TiO 4 (A = Na or Li, Ln = y or Rare-Earth)

Sang Hoon Song, Kyunghan Ahn, Mercouri G. Kanatzidis, José Antonio Alonso, Jin Guang Cheng, John B. Goodenough

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Abstract

The layered perovskite compounds NaLnTiO4 (Ln = Y, La-Tb) have Ln2O2 rock-salt layers alternating with Na 2O2 rock-salt layers on either side of a TiO2 sheet. The cation ordering introduces an internal electric field perpendicular to the layers. Ion exchange of Li+ for Na+ changes the rock-salt Na2O2 layers into OLi2O antifluorite layers but does not change the charge of the layers or, significantly, the internal electric field. The internal fields induce a ferroic displacement of the Ti(IV) ions toward the alkali-ion layers. Reversible Li insertion is observed in both NaLixLnTiO4 and Li 1+xLnTiO4 with 0 ≤ x ≤ 1; the voltage profiles show Ti(IV)/Ti(III) redox plateaus at 0.5 and 0.1 V vs Li+/Li0 and a 4f6/4f7 Eu3+/Eu2+ plateau at 0.8 V vs Li+/Li0. The shift of 1 eV in the Ti(IV)/Ti(III) redox energy relative to that found in the spinel Li4Ti 5O12 could be attributed to a capacitance energy associated with the formal +2e and -2e charges on the Ln2O 2 layers and the alkali-ion layers, respectively. Optical measurements showed that the energy gap between the Ti 3d0 and O 2p6 band edges is not significantly different in the layered and spinel titanates.

Original languageEnglish
Pages (from-to)3852-3857
Number of pages6
JournalChemistry of Materials
Volume25
Issue number19
DOIs
Publication statusPublished - Oct 8 2013

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Keywords

  • Li-insertion potentials
  • cation order
  • ion-exchange
  • layered titanates

ASJC Scopus subject areas

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

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