Formation of oxygen vacancies in ceria-zirconia nanocrystals studied by spectroscopic techniques

Abstract

Incorporation of doped ions with different ionic radius (like Zr⁴⁺) or valence state (like Eu³⁺) into CeO₂ structure leads to sufficient modification of the processes of oxygen transport due to formation of additional oxygen vacancies (Ov). These vacancies can form complexes with doped ions (RE-Ov-RE) or cerium ions (Ce³⁺-Ov-Ce³⁺) determining the oxygen mobility in these structures. In the paper the formation of oxygen vacancies in ceria (CeO₂-x) and ceria-zirconia (CeO₂-ZrO₂) nanocrystals was studied by conventional spectroscopic techniques. Ratio between intensities of ⁵D₀->⁷F₁ and ⁵D₀→⁷F₂ spectral lines of Eu³⁺ ions was used for determination of the content of oxygen vacancies and their location within ceria-zirconia nanocrystal. It was shown that while high-temperature treatment of 50 nm ceria nanocrystal in reducing atmosphere leads only to slight change of the content of oxygen vacancies which are formed preferably near its surface, incorporation of 20 % of zirconium ions is manifested in almost tenfold increase of the content of oxygen vacancies as compared to CeO₂-x nanocrystal, and these vacancies are formed within whole nanoparticle.