Incorporation of Sb⁵⁺into CeO₂: local structural distortion of the fluorite structure from a pentavalent substituent

Abstract

Hydrothermal crystallisation of CeO2 from aqueous sodium hydroxide solution at 240 °C using CeCl3·7H2O in the presence of hydrogen peroxide with addition of either SbCl3 or SbCl5 yields polycrystalline samples of antimony-containing ceria directly from solution. Powder X-ray diffraction shows a contraction of the cubic lattice parameter with increasing Sb content, and also a broadening of Bragg peaks, from which Scherrer analysis yields crystallite domain sizes of 5-20 nm. Scanning transmission electron microscopy provides consistent results with observation of highly crystalline particles of a few nm in diameter. X-ray absorption near edge structure spectroscopy at the Ce LIII- and Sb K-edges reveals the presence of Ce4+ and Sb5+ in the solids. To balance charge the presence of co-included Na is proposed, corroborated by elemental analysis. The general chemical formula of the materials can thus be written as (Ce1-xSbx)1-yNayO2-δ (where x < 0.4 and y ≥ x/3). Sb K-edge extended X-ray absorption fine structure spectroscopy of the substituted ceria samples shows that the local structure of Sb resembles that in NaSbO3, where six-coordinate metal sites are found, but with evidence of a longer interatomic correlation due to surrounding Ce/Sb atoms in the fluorite structure; this implies that the Sb is displaced from the ideal eight-coordinate site of the fluorite structure. This structural distortion gives materials that are unstable under reducing conditions, coupled by the ease of reduction to elemental antimony, which is extruded leading to phase separation.

Solvothermal Synthesis Routes to Substituted Cerium Dioxide Materials

“…This was found the oxygen storage capacity of these materials. Unlike bismuth, which is found in the +3 oxidation state when included in ceria, the earlier member of Group 15, antimony, has been shown to be present in the +5 oxidation state: this is the case whether SbCl 3 or SbCl 5 is used under hydrothermal conditions in the presence of NaOH and H 2 O 2 [99]. Here, like the case of niobium mentioned above, the co-substitution of sodium is found to balance the charge of the pentavalent substituent, resulting in chemical formulae (Ce 1−x Sb x ) 1−y Na y O 2−δ (where x < 0.4 and y ≥ x/3).…”

Determining the maximum lanthanum incorporation in the fluorite structure of La-doped ceria nanocubes for enhanced redox ability

“…Ceria nanomaterials have attracted much attention due to their extraordinary reactivity, stemming from the capacity to store and release oxygen ions depending on the oxygen partial pressure of the environment. [1][2][3][4][5][6] This reactivity originates from the labile and reversible redox cycle between Ce 4+ and Ce 3+ , which is enhanced at the nanoscale and generates the equilibrium given in eqn (1), using the Kröger-Vink notation:…”