Vibrational spectrum and X-ray diffraction studies of CeZrO4 phase with an ordered arrangement of Ce and Zr ions prepared by graphite reduction

Abstract

A series of binary CeO2–ZrO2 compounds with the composition of Ce/Zr = 1:1 (molar ratio) were reduced by graphite powders at various reducing temperatures (1173 ≤ Tred. ≤ 1573 K) for 24 h in a self-made reducing device. The reduced products obtained at various Tred. were characterized by X-ray diffraction and Vibration Spectrum. In the case of 1223 ≤ Tred. ≤ 1573 K, the reduced phase is identified as the k-CeZrO4 phase with the space group of P213, in which Ce and Zr ions are in an ordered arrangement similar to that of the pyrochlore Ce2Zr2O7, and the ordering level between Ce and Zr ions in the pyrochlore-type k-CeZrO4 phase decreased with the decreasing Tred.. The phase is stabilized without decomposition down to room temperature; the reason is attributed to the reducing atmosphere retention caused by graphite until the end of experiment. In the case of Tred. < 1223 K, a phase transition from k-CeZrO4 phase to t′-Ce0.5Zr0.5O2 phase was observed. The formation of t′ phase is due to the fact that the reducing atmosphere is too weak to severe enough to yield Zr4+/Ce4+ cation ordered configurations. The graphite reducing mechanism is discussed in the paper.