Optical Studies on the Phase Transitions in YBaMn2O6 Single Crystals

The double perovskite YBaMn2O6 exhibited complex structural, magnetic, and charge/orbital ordering phase transitions. In this paper, we investigated the correlation between the temperature-dependent optical response and complex phase transitions of YBaMn2O6 single crystals through spectroscopic ellipsometry and Raman scattering spectroscopy. The room temperature optical absorption spectrum of YBaMn2O6 revealed three bands of approximately 1.50, 4.05, and 5.49 eV. The lowest optical absorption band was assigned to on-site d-d transitions in Mn ions, whereas the other two optical features were assigned to charge-transfer transitions between the 2p states of O and 3d states of Mn. The room temperature Raman scattering spectrum revealed 25 phonon modes. Notably, the MnO6 octahedral tilting and bending modes between 360 and 440 cm-1 increased in intensity at temperatures