Composites of equiatomic Y, La, Ce, Nd, and Gd rare earth oxides: Chemical-shift effects and valence spectra

Abstract

The core-electron and valence spectra of the composites of equiatomic rare earth oxides (equi-REO) were investigated using XPS. Equi-REOs fabricated by annealing at 1600 °C for 10 h after the synthesis by mechanical ball-milling and chemical sol-gel methods, exhibited the FCC bixbyite single phase. It was confirmed that Y and La sites had the higher oxidation state (Y > 3+ and La>3+) than Y2O3 (Y3+) and La2O3 (La3+), respectively, and both Gd and Nd sites had the lower oxidation state (Gd < 3+ and Nd<3+) than Gd2O3(Gd3+) and Nd2O3(Nd3+), one the other hand, in the Ce site, Ce3+ was increased compared to CeO2, and Ce3+ and Ce4+ were mixed. There were a significant changes in the electron DOS associated with O 2p – 4f hybridizations in the equi-REOs compared to the ideal mixture. Finally, we found that the chemical sol-gel process induces more changes of chemical and electronic states of the equi-REO than the mechanical ball milling process.