Influence of grain size on the vibrational properties in Mn2O3 nanocrystals

The influence of grain size on the vibrational properties of Mn2O3 nanocrystals has been investigated by transmission electron microscopy, Raman and infrared (IR) spectroscopy. It is found that the vibrational properties are sensitively dependent on the grain sizes of Mn2O3 nanocrystals. Raman spectra studies indicate that with decreasing grain sizes, allowing the transition of phonons with q ≠ 0 contributes to the Raman spectrum, which leads to the broadening of the Raman peaks in the lower frequency region. IR spectra exhibit the remarkable differences in the shapes with different grain sizes of Mn2O3 nanocrystals. The shape of the band in the 570–670 cm−1 ranges is strongly evocative of transverse-optical (TO) and longitudinal-optical (LO) splitting. This splitting appears more and more clear with the decreasing grain size of Mn2O3 nanocrystals.