| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1490487 | Materials Research Bulletin | 2011 | 7 Pages |
Nickel manganite powder synthesized by calcination of a stoichiometric mixture of manganese and nickel oxide was additionally mechanically activated in a high energy planetary ball mill for 5–60 min in order to obtain a pure NiMn2O4 phase. The as-prepared powders were uniaxially pressed into disc shape pellets and then sintered for 60 min at 1200 °C. Changes in the particle morphology induced by mechanical activation were monitored using scanning electron microscopy, while changes in powder structural characteristics were followed using X-ray powder diffraction. The ac impedance spectroscopy was performed on sintered nickel manganite samples at 25 °C, 50 °C and 80 °C. It was shown that mechanical activation intensifies transport processes causing a decrease in the average crystallites size, while longer activation times can lead to the formation of aggregates, defects and increase of lattice microstrains. The observed changes in microstructures were correlated with measured electrical properties in order to define optimal processing conditions.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The influence of mechanical activation on microstructure evolution in the nickel manganite powder was investigated as well as electrical properties of the sintered samples. ► Structural refinement obtained by Topas-Academic software based on Rietveld analysis showed that the milling process remarkably changed the powder morphology and microstructure. ► SEM studies of sintered samples also revealed the strong influence of milling time on ceramics density (increases with milling time). ► The electrical properties of ceramic samples are clearly conditioned by terms of synthesis, in our case the time of mechanical activation. ► The highest density and higher values of dielectric constant were achieved at the sample activated for 45 min.
