Far infrared and microstructural studies of mechanically activated nickel manganite

Nickel manganite powder synthesized by calcination of a stoichiometric mixture of manganese (MnO Aldrich 99.9%) and nickel oxide (NiO Merck, 99.5%) containing 0.5 wt% CoO and Fe2O3, was additionally mechanically activated in a high energy planetary ball mill for 5–60 min. The resulting powders were uniaxially pressed into disc shape pellets and then sintered for 60 min at 900 °C, 1050 °C and 1200 °C. Morphological changes of the obtained nickel manganite ceramics induced by mechanical activation were monitored using scanning electron microscopy, while changes in structural characteristics were followed using X-ray powder diffraction. Room temperature far infrared reflectivity spectra for all sintered samples were recorded in the frequency range between 50 cm−1and 1200 cm−1. The observed spectra for all samples showed the presence of the same oscillators, but their intensities depended on the sintering temperature and the time of mechanical acivation. Transversal and longitudinal optical modes were calculated for six ionic oscillators (four strong, and two shoulders) belonging to the nickel manganite partially inverse spinel structure.