Preparation and characterization of praseodymium calcium manganate

摘要

The magnetoresistive manganese oxide, Pr_(0.46)Ca_(0.54)MnO_3 was synthesized by a sol-gel process involving a stable metal chelate complex with acetylacetone. Manganese(Ⅲ), calcium(Ⅱ) 2,4-pentadionate and praseodymium nitrate were readily dissolved and mixed in solution. Since the type of ligand could affect the type of bonding in the mixed oxide materials, the structural evolution of the reaction mixture was monitered by carbon-13 nuclear magnetic resonance (~(13)C NMR) and Fourier transform infrared (FT-IR) spectroscopy. The calcining temperature was determined from differential scanning calorimetry (DSC) and thermogravimetric analysis. The crystallized powders were examined by X-ray diffractometry (XRD) and Rietveld profile fitting. The microstructure and morphology were characterized by scanning electron microscopy/energy-despersive (X-ray) spectrometry (SEM/EDS) and found to be homogeneous. Transmission electron microscopy/selected area diffraction (TEM/SAD) observed charge ordering at 180 K which disappeared by room temperature. The magnetic properties were investigated as a function of temperature and found to be consistent with TEM/SAD and XRD observations.