Raman spectroscopy study of in situ change in laser irradiated LiMn2O4

A spinel LiMn2O4 is investigated via Raman spectroscopy at 514.5-nm excitation and X-ray diffraction. The dependence of Raman spectra on the different irradiated laser powers is determined and found to be different from that at 632.8-nm excitation. Based on our extensive analysis, our experimental results can be attributed to the laser heating effect, which reduces the Mn4+ cation concentration in the local area. Consequently, the decrease in average Mn valence in the local area unavoidably induces the Jahn-Teller effect and local lattice distortion, which accounts for the evolution of the measured Raman spectra of spinel LiMn2O4.