Control of oxygen vacancies and Ce+3 concentrations in doped ceria nanoparticles via the selection of lanthanide element

Abstract

The effect of lanthanides that have positive association energies with oxygen vacancies, such as samarium and neodymium, and the elements with negative association energies, such as holmium and erbium, on ionization state of cerium and, consequentially, the oxygen vacancy concentration in doped ceria nanoparticles are investigated in this article. Structural and optical characterizations of the doped and undoped ceria nanoparticles, synthesized using chemical precipitation, are carried out using transmission electron microscopy, X-ray diffractometry, optical absorption spectroscopy, and fluorescence spectroscopy. It is deduced that the negative association energy dopants decrease the conversion of Ce ?4 into Ce ?3 and, hence, scavenge the oxygen vacancies, evidenced by the observed increase in the allowed direct bandgap, decrease in the integrated fluorescence intensity, and increased the size of doped nanoparticles. The opposite trends are obtained when the positive association dopants are used. It is concluded that the determining factor as to whether a lanthanide dopant in ceria acts as a generator or scavenger of oxygen vacancies in ceria nanoparticles is the sign of the association energy between the element and the oxygen vacancies. The ability to tailor the ionization state of cerium and the oxygen vacancy concentration in ceria has applications in a broad range of fields, which include catalysis, biomedicine, electronics, and environmental sensing.

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

“…Since only isolated defects were calculated, this could account for the disparity between the experimental and calculated frequencies. The possibility of the intrinsic surface peroxide species being present in reduced CeO 2 at high oxygen partial pressures may be significant for understanding CeO 2 catalysis, as previous studies have only considered reactions through the O vacancy [17,13,41] or through adsorbed peroxo/superoxo species. [42,43,40] Having demonstrated that alternative oxygen states to the O vacancy are valid defect structures on reduced pure CeO 2 surfaces, the La-doped CeO 2 surfaces were also investigated to examine whether these peroxide species are a viable mechanism for charge compensation.…”

Effect of Mg doping and sintering temperature on structural and morphological properties of samarium-doped ceria for IT-SOFC electrolyte

“…The weak intensities occurring in the range 3550-3400 and 1600-1300 cm -1 can be assigned to O-H stretching vibrations of hydroxyl group, probably due to moisture content of KBr, as KBr is hydroscopic absorbs more humidity in the atmosphere. The strong bands at around 850-450 cm -1 can be attributed to characteristic Ce-O vibrations (Shehata et al 2012;Ainirad et al 2011;Arabaci and Oksuzomer 2012). The intensities of all other bands at 3550-3400 and 1600-1300 cm -1 have been reduced significantly because of high sintering temperature of 1100°C due to which the adsorbed water has been removed and improving the crystallinity of the samples.…”

Mg Doping Induced Effects on Structural, Optical, and Electrical Properties as Well as Cytotoxicity of CeO2 Nanostructures

“…Furthermore, Mg doping can lead to a higher abundance of Ce 4+ ions as compared to Ce 3+ ions in the CeO 2 matrix, which can also result in widening of its band gap. [39] To study the Mg doping induced effects on the electrical characteristics of CeO 2 nanostructures, the AC conductivities of all the prepared samples have been determined and shown in Figure 5. Figure 5 shows the variation of AC conductivity of all the prepared nanostructures as a function of AC frequency at room temperature.…”