We have measured water uptake and hydration enthalpy in 50% La and Nd doped CeO₂, also to be taken as compositions in the series La_2−xNd_xCe₂O₇ (x = 0.0, 0.5, 1.0 and 2.0) using combined thermogravimetry (TG) and differential scanning calorimetry (DSC), TG-DSC. The TG-DSC data unambiguously yield standard molar hydration enthalpies of ~−74 kJ/mol independent of water uptake. The interpretation of the TG results, however, does not fit a classical model of hydration of all oxygen vacancies. Instead, the hydration appears to be limited to a small fraction of the free vacancies. Hydration further decreases as the Nd content (x) and long-range order increases and regions of disorder decrease. We propose a new model explaining why hydration occurs only in a small fraction of the nominally free vacancies: The higher basicity of La/Nd compared to Ce promotes protonation at oxide ion sites with high coordination to La/Nd, and the observed water uptake and modelling suggests that mainly oxide ions fully coordinated to 4 La/Nd neighbours become protonated. The statistical variation of coordination around oxygen sites in a disordered fluorite oxide creates a limited number of such oxide ions sites which results in limited hydration. The model matches well the experimental results and DFT calculations of proton trapping at the fully La-coordinated sites for 50% La-doped CeO₂, and also rationalizes conductivity data.

我们已经测量了掺有50％La和Nd的CeO _2中的吸水率和水合焓，也将La _{2− x} Nd _x Ce ₂ O ₇（x  = 0.0、0.5、1.0和2.0）系列中的组成作为组合使用热重法（TG）和差示扫描量热法（DSC），TG-DSC。TG-DSC数据清楚地表明，与吸水量无关，标准摩尔水合焓为〜-74 kJ / mol。然而，TG结果的解释并不适合所有氧空位的水合的经典模型。相反，水合似乎仅限于自由空位的一小部分。随着Nd含量（x），远程顺序增加，无序区域减少。我们提出了一个新的模型，解释了为什么水合仅发生在名义上空位的一小部分：与Ce相比，La / Nd的更高的碱度促进了与La / Nd高度配位的氧化物离子位点的质子化，并且观察到了水的吸收和建模表明，主要与4个La / Nd邻域完全配位的氧化物离子会质子化。在无序的萤石氧化物中氧位点周围配位的统计变化产生了数量有限的这种氧化物离子位点，从而导致水化作用受限。该模型与50％La掺杂的CeO ₂在完全La配位的位置处的质子俘获的实验结果和DFT计算非常吻合，并且使电导率数据合理化。