Abstract

Optical absorption spectra of cubic spinel LiMn2O4 and its delithiated form λ-MnO2 are determined using photoacoustic spectroscopy. Eight absorption peaks, in the wavelength range of 375-800 nm, associated with the O 2p-Mn t2g, O 2 p-Mn eg, and Mn t2g-Mn eg band transitions are identified for LiMn2O4 and λ-MnO2. Upon deintercalation of LiMn2O4, the peaks at the high energy side of the absorption spectrum (375-565 nm) are blueshifted, whereas those at the low energy side (570-800 nm) are redshifted. The observed effects are explained on the basis of nonrigid band model, suggesting a change in oxygen ionicity during lithium deintercalation. © 2007 American Institute of Physics.