Department of Physics and Astronomy, Uppsala University, Box 516, 75121 Uppsala, Sweden.
Phys Chem Chem Phys. 2018 May 3;20(17):11805-11818. doi: 10.1039/c8cp01029c.
We present the phase diagram of Ce1-xGdxO2-x/2 (CGO), calculated by means of a combined Density Functional Theory (DFT), cluster expansion and lattice Monte Carlo approach. We show that this methodology gives reliable results for the whole range of concentrations (x ≡ xGd ≤ 1). In the thermodynamic equilibrium, we observe two transitions: the onset of oxygen-vacancy (O-Va) ordering at ca. 1200-3300 K for concentrations xGd = 0.3-1, and a phase separation into CeO2 and C-type Gd2O3 occurring below ca. 1000 K for all concentrations. We also model 'quenched' systems, with cations immobile below 1500 K, and observe that the presence of random-like cation configurations does not prevent C-type vacancy ordering. The obtained transition temperatures for Va ordering agree rather well with existing experimental data. We analyse the effect of vacancy ordering and composition on the lattice parameters and relaxation pattern of cations.
我们提出了 Ce1-xGdxO2-x/2 (CGO) 的相图，通过组合密度泛函理论（DFT）、团簇展开和晶格蒙特卡罗方法计算得到。我们表明，这种方法对于整个浓度范围（x ≡ xGd ≤ 1）都能给出可靠的结果。在热力学平衡中，我们观察到两个转变：大约在 1200-3300 K 时氧空位（O-Va）有序开始，对于浓度 xGd = 0.3-1，以及低于大约 1000 K 时分为 CeO2 和 C 型 Gd2O3 的相分离。我们还模拟了在 1500 K 以下阳离子不移动的“淬火”系统，并观察到随机阳离子构型的存在并不能阻止 C 型空位有序化。Va 有序化的转变温度与现有的实验数据相当吻合。我们分析了空位有序化和组成对晶格参数和阳离子弛豫模式的影响。
