Synthesis and full characterization of the phase-pure pyrochlore Ce2Zr2O7 and the K-Ce2Zr2O8 phases

The K-Ce2Zr2O8 phase has been synthesized starting from t-Ce0.5Zr0.5O2 solid solution which is reduced by hydrogen at high temperatures to form the pyrochlore Ce2Zr2O7 phase (pyr-Ce2Zr2O7) with high degree of ordering of the cationic sublattice. The final step in the synthesis of the K-Ce2Zr2O8 phase includes a mild re-oxidation of pYr-Ce2Zr2O7 at around 600 C under atmospheric conditions. Yet, the synthesis of phase-pure K-Ce2Zr2O8 phase (Phase-pure and with highest ordering) is still not settled since most of the previous studies used reduction temperatures of 1300 degrees C and below. We show in this contribution that 1300 degrees C is not sufficient to warrant the preparation of phase-pure pyr-Ce2Zr2O7 and K-Ce(2)Zr(2)O8, but that rather temperatures as high as 1500 degrees C are required to assure phase purity of both phases. This conclusion is drawn from extended X-ray diffraction and X-ray absorption spectroscopy analyses together with Raman spectroscopy, providing in-depth details of the structure on the level of both, the evolution of the special periodic structure and the coordination of the metal atoms. (C) 2016 Elsevier B.V. All rights reserved.