Eu3+/Eu2+ redox energy in a new lithium intercalation compound LixEuTa7O19 (0 <= x <= 1)

Abstract

Electrochemical lithium intercalation is observed in LixEuTa7O19 with 0 <= x <= 1; the voltage profiles show a 4f(6)/4f(7) Eu3+/Eu2+ redox plateau at 1.85 V versus Li+/Li-0. The shift of 1 V in the Eu3+/Eu2+ redox plateau relative to that found in the layered perovskite LiEuTiO4 (0.85 V versus Li+/Li-0) can be attributed to a capacitance energy stored in the three parallel planes (Eu2O2)(2+)-(TiO2)(0)-(Li2O2)(2-) in LiEuTiO4. Optical measurements show that the energy gaps between the Eu: 4f(6) and O:2p(6) band edges for LiEuTiO4 and EuTa7O19 are 3.86 and 3.94 eV, respectively.