阳离子有序相Ce2Zr2O7.97的石墨还原制备及其结构表征

采用石墨还原法探索了CeO₂-ZrO₂二元体系在不同还原温度、还原时间条件下的物相组成及结构，借助X射线衍射、红外振动光谱等手段对还原样品进行了物相表征及结构分析。实验结果表明：通过石墨还原能在较低温度（T_red＝1050 ℃）、较短时间（t＝24 h）内合成纯相Ce₂Zr₂O_7.97，较传统先还原（95%Ar+5%H₂，T_red≥1400℃，t＞48 h）后氧化（O₂或空气气氛）工艺更简单经济；Ce₂Zr₂O_7.97相能在1050～1300 ℃、24～72 h还原条件下稳定存在并保留至室温而不发生相分解，其机制可能归因于石墨所形成的弱还原环境；Ce₂Zr₂O_7.97相拥有与烧绿石Ce₂Zr₂O₇相近的有序阳离子亚晶胞结构，但由于其氧空位（O3、O4、O11）被大部分氧离子所填充，导致该相结构对称性降低。本文提出的石墨还原法制备富氧相Ce₂Zr₂O_7.97有望成为一种较传统制备工艺更简单经济的新方法，而Ce₂Zr₂O_7.97相能在还原气氛中稳定存在，可为An₂Zr₂O_7+x固化体的存放环境提供借鉴和参考。

Fabrication by Graphite Reduction and Structure Characterization ofCe2Zr2O7.97 Phase Possessing Ordered Cation Ions

The phase composition and phase structure of CeO₂-ZrO₂ binary system were studied via graphite reduction method under different reducing temperatures and time. The various reduced products were characterized by powder X-ray diffraction and infrared spectra. Experimental results show that Ce₂Zr₂O_7.97 phase can be synthesized successfully at a relative low temperature (T_red＝1050 ℃) and short time (t＝24 h) by graphite reduction method, which is more simplified and economic than traditional reduction-reoxidation method with Ar-H₂ (5% V/V hydrogen in argon) reduction atmosphere. Ce₂Zr₂O_7.97 phases prepared in a temperature range of 1050-1300 ℃ for 24-72 h are stable and can be retained until room temperature without phase decomposition. The mechanism may be attributed to a weak reduction environment formed by graphite. Ce₂Zr₂O_7.97 phase with an ordered cation sub unit cell structure is similar with pyrochlore Ce₂Zr₂O₇, but the structure symmetry of Ce₂Zr₂O_7.97 phase is lower than that of pyrochlore Ce₂Zr₂O₇ due to the oxygen vacancy (O3, O4, O11) filled partially. Graphite reduction method is expected to become a new, simple and economical preparation method comparing with the traditional preparation process for Ce₂Zr₂O_7.97. The Ce₂Zr₂O_7.97 phase retained at room temperature in a weak reducing atmosphere can provide a reference for the storage environment of An₂Zr₂O_7+x waste forms.