Lattice Dynamics and Vibrational Spectra of Lithium Manganese Oxides:  A Computer Simulation and Spectroscopic Study

Abstract

The lattice vibrational modes of spinel-structured lithium manganese oxides have been calculated using atomistic modeling methods. The simulations allow the Raman and infrared spectra of lithiated, fully delithiated, and partially delithiated phases to be assigned for the first time. Calculations for the spinels LiMn2O4, λ-MnO2, and Li0.5Mn2O4 are compared with experimental Raman data measured for thin films of the oxides coated on a platinum electrode. The appearance of a number of new bands in the Raman spectrum of LiMn2O4 following partial extraction of lithium is shown to result from local lowering of the symmetry and Raman activation of modes which are optically inactive or only infrared active in LiMn2O4. The results support a model for the Li0.5Mn2O4 lattice in which the lithium ions are ordered. The deformation vibrations of lattice hydroxyl “defects” in λ-MnO2 have also been calculated; comparison of the calculated and experimental vibrational data supports a model in which hydroxyl species are localized at octahedral Mn vacancies.

Palladium doped perovskite-based NO oxidation catalysts: The role of Pd and B-sites for NOx adsorption behavior via in-situ spectroscopy

“…The former features at 210 and 421 cm −1 can be associated with A 1g and E g modes of oxygen cage rotation and vibration in LaMnO 3 perovskite, respectively [25]. Another Raman feature at 644 cm −1 can be attributed to a Mn-O-Mn stretching mode ( Mn-O-Mn ) in the perovskite structure in accordance with Li et al [26] who reported a similar peak at 654 cm −1 for Mn 3 O 4 , as well as Ammundsen et al [27] who also reported a Raman signal at 647 cm −1 for MnO 2 . Furthermore, this assignment is also consistent with the previously published Raman data on Pd/LaMnO 3 [28] which revealed a major signal at 653 cm −1 .…”

Electronic structure and optical band gap of CoFe2O4 thin films

“…In fact, except for small differences in phonon line parameters, the spectra and their variation as a function of the film thickness closely resemble to those of bulk . According to the factor group analysis these phonon lines correspond to the optical active Raman modes ( 3 ) of cubic spinel with 3 space group [13]. For cubic spinel, the mode is assigned to the motion of oxygen in the tetrahedra due to the symmetric stretching of oxygen atom with respect to metal ion in 6 tetrahedral void.…”

Modeling and Simulation in Spectroscopic Study

“…Two higher wave number modes at 517 and 633 cm −1 are attributed to T 1u (3) and T 1u (4), and two lower wave number modes at 287 and 383 cm −1 are ascribed to T 1u (1) and T 1u (2). Experimentally, the former , easily resolved in the mid-infrared region.…”

“…The A 1g and E g vibrations involve only oxide ion displacements. The T 2g (2) and T 2g (3) phonons are characterized by large oxygen motions and very small Li displacements, but the lowest energy T 2g (1) phonon derives predominantly from a vibration of the Li sublattice.…”