Angle-Resolved Photoemission Study of Lithium Solid-Electrolytes Bulk Single Crystals

We performed angle-resolved photoemission spectroscopy (ARPES) measurements of lithium solid-electrolytes LixLa(1−x)/3NbO3 (x ~ 0 [LNbO], 0.08 [LLNbO]) and Li3xLa2/3−xTiO3 (LLTO) (x ~ 0.06) to systematically study the valence band structure related to the ionic conduction properties. Under sufficiently suppressed photon flux condition (3E10 photons/s), we succeeded in observing valence band dispersions, which are similar between LNbO and LLNbO, while LLTO exhibits a clear difference. From a comparison with the DFT calculations, we found qualitative similarities with the ARPES results. However, the gap size and bandwidth exhibit a mismatch, possibly due to the electron correlation effect. Furthermore, under high-flux photon irradiation condition (1E12 photons/s), anomalous spectral modulations were observed for LLNbO and LLTO. A two-step model is discussed as the possible origin of the observed spectral modulation: (1) the formation of Li+ ions by the dissociation of Li bonding states and (2) diffusion/migration of Li+ ions to the surface.