Combustion synthesis, structural and magnetic characterization of Ce_(1−x)Pr_xO_2 system

摘要

The current work describes the synthesis of Ce_(1−x)Pr_xO_2 (x = 0.0, 0.2, 0.4, 0.6, 0.8) and Pr_6O_(11) systems by the combustion method, using citric acid as chelating agent. The obtained solids after combustion and calcination processes were characterized by thermal analysis (TGA-DTA) and infrared spectroscopy (FT-IR) to evaluate the chemical process during the combustion reaction. The surface area analysis using isotherms of nitrogen adsorption, reveal that all samples exhibit values between 70 and 135 m~2 g~(−1), with a pore volume that allows its classification as mesoporous materials. The structural analysis by X-ray diffraction (XRD) and Rietveld refinement, revealed the obtention of a pure cubic structure Fm3m (225) along all cerium oxide modifications with nanocrystalline domain sizes, except for the praseodymium oxide that shows two crystalline phases in a monoclinic crystalline phase P12_1/c 1 (14) in the case of Pr_6O_(11) and a cubic phase Fm3m (225) for PrO_2 oxide. The oxygen storage capacity measurements performed in all samples, demonstrate that exchange of Ce ions by Pr increases the storage capacity of samples over the reference values in accordance with the synthesis method. The characterization by high-resolution transmission electron microscopy, confirmed that the solids are composed by nanometric aggregates with d spacing between 0.29 and 0.31 nm along main diffraction signals, in accordance with the experimental XRD results. Finally, the magnetic characterization in a ZFC configuration and a M-H mode, shows a strong paramagnetic behavior in all systems except in CeO_2 oxide, which exhibited a prevalent diamagnetic behavior.