铈锆固溶体中的相分离和表面偏析
Phase separation and surface segregation in ceria-zirconia solid solutions
摘要：
结合使用密度泛函理论计算和统计力学，我们表明，范围广泛的中间组成的氧化铈-氧化锆固溶体是热力学亚稳相对于相分离成富铈和富锆的氧化物。我们估计，在1373 K的CeO 2中的Zr的最大平衡浓度为~ 2%，因此具有较高Zr含量的平衡样品预计将表现出在原子尺度上的异质性。我们还表明，在（111）表面附近，在高温下的阳离子再分布将发生显着的Ce富集的表面，我们归因于更多的Zr-O键的共价特性相比，Ce-O键。尽管阳离子扩散的动力学屏障通常防止氧化铈-氧化锆固溶体在典型催化应用中的分解/分离，但本文所述的分离行为可预期发生在现代三元催化转化器中，其中达到非常高的温度。
英文摘要：
Using a combination of density functional theory calculations and statistical mechanics, we show that a wide range of intermediate compositions of ceria - zirconia solid solutions are thermodynamically metastable with respect to phase separation into Ce-rich and Zr-rich oxides. We estimate that the maximum equilibrium concentration of Zr in CeO2 at 1373 K is ~2%, and therefore equilibrated samples with higher Zr content are expected to exhibit heterogeneity at the atomic scale. We also demonstrate that in the vicinity of the (111) surface, cation redistribution at high temperatures will occur with significant Ce enrichment of the surface, which we attribute to the more covalent character of Zr-O bonds compared to Ce-O bonds. Although the kinetic barriers for cation diffusion normally prevent the decomposition/segregation of ceria-zirconia solid solutions in typical catalytic applications, the separation behaviour described here can be expected to occur in modern three-way catalytic converters, where very high temperatures are reached.
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