Modulation of the Optical Properties of Lithium Manganese Oxide via Li‐Ion De/Intercalation

Abstract The optical response of lithium manganese oxide (LiMn₂O₄, LMO) on intercalation with Li ions is quantitatively characterized. For this purpose, a layer of LMO and a layer of platinum, acting as current collector/reflector, are deposited on oxidized silicon wafers. The active layer is structurally characterized using X‐ray diffractogram and transmission electron microscopy. Well‐defined intercalation states are prepared electrochemically and investigated by optical spectrometry in reflectance geometry. The measured dispersion curves are described by the Clausius–Mossotti dispersion equation to derive the complex refractive index as a function of wavelength and intercalation state. The observed variation of the effective resonant wavelength is consistent with the change in the band structure of LMO with lithium intercalation. Furthermore, the electrochromic reversibility is demonstrated in situ during the electrochemical reaction. From the calculations, a 1350 nm thick layer of LMO is sufficient to cause a phase shift of π at a wavelength of 750 nm, which indicates the material as a promising candidate to perform reliable optical switching.