Further findings of X-ray absorption near-edge structure in lithium manganese spinel oxide using first-principles calculations

Abstract

X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides Li_xMn₂O₄ (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn₂O₄ models, the contributions of the Mn³⁺ ion and Mn⁴⁺ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn³⁺Mn⁴⁺)O₄ and de-intercalated Li_0.5(Mn³⁺_0.5Mn⁴⁺_1.5)O₄ and Mn⁴⁺₂O₄ (λ-MnO₂). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn₂O₄ to tetragonal I4₁/amd Li₂Mn₂O₄) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.