Remarkable Effects of Lanthanide Substitution for the Y-Site on the Oxygen Storage/Release Performance of YMnO3+δ

摘要

Lanthanide-substituted YMnO_(3+δ) nanoparticles with the hexagonal phase, denoted as R_(0.25)Y_(0.75)MnO_(3+δ) (R = Er, Dy, Tb, Gd, and Sm), have been successfully synthesized by the polymerized complex method. The substitutions did not largely affect the morphologies and specific surface area of the obtained R_(0.25)Y_(0.75)MnO_(3+δ) nanoparticles. From the evaluation for the oxygen storage/release properties, the oxygen storage capacity (OSC) increased significantly by the Tb substitution, and the oxygen absorption/release rate strongly depended on the ion size of the substituted lanthanides. It was found that Tb~(4+) existed in Tb_(0.25)Y_(0.75)MnO_(3+δ) after oxygen absorption, demonstrating that the remarkable increase in the OSC of the Tb-substituted sample was due to the oxidation of not only Mn~(3+) to Mn~(4+) but also Tb~(3+) to Tb~(4+). In addition, the unit cell volume increasing with the R ion size, which can lead to the promotion of the oxygen diffusion in the crystal structure, was the factor leading to the increase of the oxygen absorption rate. Especially, Sm_(0.25)Y_(0.75)MnO_(3+δ) showed an excellent OSC of 3 + δ = 3.34 (the weight increase rate was 2.64 wt %) even under a rapid temperature swing rate of 20 °C/min.