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

The influence exerted by specific synthesis protocol conditions on the crystal, local atomic and electronic struc-tures 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) spec-troscopies, and simultaneous thermal analysis. Cerium chromate heptahydrate [Ce+(3) (2) (Cr+O-6(4))3(H2O)(5)]center dot 2H(2)O with the monoclinic structure (sp. gr. P-21/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 degrees C leads to the formation of a mixture of CeO2 and Cr2O3 phases. The calcination in vacuum at 1200 degrees C affords CeCrO3 (with the orthorhombic structure, sp. gr. Pnma(62)), which upon repeated heating to above 650-700 degrees 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+.

Automated summary

The study investigates the influence of specific synthesis conditions on the crystal, atomic, and electronic structures of Ce chromates/chromites prepared using coprecipitation. Various analytical techniques, including synchrotron X-ray diffraction, X-ray absorption fine structure (XAFS), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and simultaneous thermal analysis, were used. It was found that different synthesis conditions resulted in the formation of different phases, such as CeO2, Cr2O3, and CeCrO3, and accompanied redox transformations of Cr6+ -> Cr3+ and Ce3+ <-> Ce4+.