Effect of lithium concentration on the thermal and optical properties of LixMn2O4 by photoacoustic measurements

S.T. Lee , K. Raveendranath , M.R. Tomy , M. Paulraj, S. Jayalekshmi , K.P.R. Nair and J. Ravi
PHYSICAL REVIEW B 76, 11 (2007)

ABSTRACT

In the present work, pellets of LixMn2O4 polycrystalline powder samples with x=0.8, 0.9, 1.0, 1.1, and 1.2 are analyzed to understand the effect of lithium concentration on the thermal and optical properties, and the electronic structure of LixMn2O4 predicted in an earlier work using full-potential linear muffin-tin orbital (FP-LMTO) method is experimentally verified. The experimental tool used for the determination of the thermal and optical properties is the well-known photoacoustic technique. The variation of thermal diffusivity with changing x values in LixMn2O4 is extensively studied to explain the influence of lithium concentration on the thermal properties, and has been correlated with the structural asymmetry and defects in LixMn2O4. The optical absorption spectrum, being the signature of the electronic structure of materials, is recorded in the visible range (350-800 nm). Six prominent absorption peaks associated with the O 2p-Mn t(2g), O 2p-Mn e(g), and Mn t(2g)-Mn e(g) band transitions for LixMn2O4, with x <= 1, are observed experimentally, substantiating the electronic structure predicted by the FP-LMTO method. However, it is observed that there are more absorption peaks in the case of Li1.1Mn2O4 and Li1.2Mn2O4, which is attributed to the structural distortion from pure cubic spinel structure to a mixture of spinel and tetragonal structures, which is verified by the x-ray diffraction spectra.

DOI: http://dx.doi.org/10.1103/PhysRevB.76.115112



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