Lattice and local-mode vibrations in anhydrous and protonized LiMn2O4 spinels from first-principles theory
Abstract
The phonon dispersion relations and density of states of anhydrous LiMn2O4 spinels have been studied using first-principles theory. Above the acoustic phonon branches, the heavy Mn ions and the light Li ions separately contribute primarily to the optic phonons of low (∼180 to 280 cm−1) and high (>400 cm−1) energies, respectively, whereas the O ions partake in lattice vibrations over a wide range of frequencies (180–644 cm−1). The measured phonon density of states of a LiMn2O4 powder corroborates the calculated results. Symmetry analysis of the calculated Brillouin-zone center modes allows a detailed comparison with the Raman- and infrared-active modes reported in the literature. First-principles calculations were also performed on protonized LiMn2O4 spinels. Each