Kazuo Inamori School of Engineering, Alfred University, Alfred, NY, 14802, USA.
Sci Rep. 2017 Jul 19;7(1):5920. doi: 10.1038/s41598-017-06407-5.
Compounds with the formulae CaZrCeTiO with x = 0.1-0.5 were synthesized by solid state reaction. Cerium was used as a surrogate for actinide elements. A transition from the 2M polymorph to the 4M polymorph (expanded unit cell due to cation ordering) in zirconolite was observed with increasing cerium content. The presence of both tri- and tetravalent Ce, contrary to formulation, was confirmed using X-ray absorption near edge spectroscopy, suggesting substitution on both Ca and Zr sites. Sintering was carried out via spark plasma sintering, during which the perovskite phase (CaCeTiO) was stabilized due to the reducing conditions of this technique. Scanning electron microscopy and energy dispersive spectrometry revealed that the 2M polymorph was dilute in Ce content in comparison to the 4M-zirconolite. High temperature X-ray diffraction was used to detail the kinetics of perovskite to zirconolite transition. It was found that CaCeTiO (cubic pyrochlore) formed as an intermediate phase during the transition. Our results show that a transition from 2M- to 4M-zirconolite occurs with increasing Ce content and can be controlled by adjusting the P and the heat treatment temperature.
采用固态反应法合成了通式为 CaZrCeTiO（x=0.1-0.5）的化合物。铈被用作锕系元素的替代物。随着铈含量的增加，钙钛矿型锆石中的 2M 多晶型向 4M 多晶型（由于阳离子有序而使单位晶胞膨胀）转变。使用 X 射线吸收近边光谱证实了不仅存在三价铈，而且还存在四价铈，这与分子式不符，这表明在 Ca 和 Zr 位都发生了取代。通过火花等离子烧结进行烧结，由于该技术的还原条件，稳定了钙钛矿相（CaCeTiO）。扫描电子显微镜和能谱分析表明，2M 多晶型的 Ce 含量比 4M-锆石型要低。高温 X 射线衍射用于详细研究钙钛矿向锆石的转变动力学。结果发现，在转变过程中形成了立方尖晶石型 CaCeTiO（钙钛矿型）作为中间相。我们的结果表明，随着 Ce 含量的增加，2M-向 4M-锆石型的转变会发生，并且可以通过调整 P 和热处理温度来控制。
