Control over crystal, local atomic and electronic structures of cerium chromates/chromites via the synthesis conditions

• Published in: Materials chemistry and physics 2023-02, Vol.296, p.127269, Article 127269
• Main Authors: Popov, V.V., Menushenkov, A.P., Zubavichus, Y.V., Dubyago, F.E., Yastrebtsev, A.A., Ivanov, A.A., Rudakov, S.G., Svetogorov, R.D., Khramov, E.V., Kolyshkin, N.A., Tsarenko, N.A., Shchetinin, I.V., Bordyuzhin, I.G.
• Format: Article
• Language: English
• Subjects: Cerium chromates/chromites; Crystal and local structures; FT-IR spectroscopy; Raman spectroscopy; Synchrotron XRD; X-ray absorption fine structure (XAFS)
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2022.127269

The influence exerted by specific synthesis protocol conditions on the crystal, local atomic and electronic structures of various types of Ce chromates/chromites prepared by the coprecipitation is studied using synchrotron X-ray diffraction, X-ray absorption fine structure (XAFS), Raman and Fourier transform infrared (FT-IR) spectroscopies, and simultaneous thermal analysis. Cerium chromate heptahydrate [Ce2+3(Cr+6O4)3(H2O)5]⋅2H2O with the monoclinic structure (sp. gr. P21/c) has been synthesized and characterized structurally for the first time. It has been established that calcination of all types of precursors in air at a temperature ≥ 450 °C leads to the formation of a mixture of CeO2 and Cr2O3 phases. The calcination in vacuum at 1200 °C affords CeCrO3 (with the orthorhombic structure, sp. gr. Pnma(62)), which upon repeated heating to above 650–700 °C in air tends to decompose into CeO2 and Cr2O3 phases. Long-range XRD data correlate well with the results of techniques sensitive to the local structure parameters, such as XAFS, Raman and FT-IR. XANES spectra measured at the Cr K- and Ce L3- edges strongly imply that the synthesis procedures are accompanied by concerted redox transformations Cr6+→ Cr3＋ and Ce3+⟷ Ce4+. [Display omitted] •The crystal, local and electronic structures of Ce chromates/chromites are studied.•A combination of s-XRD, XANES, Raman and FT-IR, STA techniques is applied.•Ce2+3(Cr+6O4)3⋅7H2O (monoclinic, P21/c) has been synthesized for the first time.•Vacuum calcination at 1200 °C affords CeCrO3 (orthorhombic, Pnma).•The synthesis is accompanied by concerted redox reactions Cr6+→ Cr3+ and Ce3+⟷ Ce4+.