J. Ravi , M. Paulraj, K. Raveendranath , M.R. Tomy , S. Jayalekshmi and S.T. Lee
AMERICAN JOURNAL OF PHYSICS 90, 16 (2007)
Optical absorption spectra of cubic spinel LiMn2O4 and its delithiated form lambda-MnO2 are determined using photoacoustic spectroscopy. Eight absorption peaks, in the wavelength range of 375-800 nm, associated with the O 2(p)-Mn t(2g), O 2(p)-Mn e(g), and Mn t(2g)-Mn e(g) band transitions are identified for LiMn2O4 and lambda-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. (c) 2007 American Institute of Physics.