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 language | English (US) |
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Pages (from-to) | 3852-3857 |
Number of pages | 6 |
Journal | Chemistry of Materials |
Volume | 25 |
Issue number | 19 |
DOIs | |
State | Published - Oct 8 2013 |
Keywords
- Li-insertion potentials
- cation order
- ion-exchange
- layered titanates
ASJC Scopus subject areas
- Chemistry(all)
- Chemical Engineering(all)
- Materials Chemistry