Vinograd Victor L, Bukaemskiy Andrey A, Modolo Giuseppe, Deissmann Guido, Bosbach Dirk
Institute of Energy and Climate Research IEK 6, Nuclear Waste Management and Reactor Safety, Forschungszentrum Jülich, Jülich, Germany.
Front Chem. 2021 Nov 8;9:705024. doi: 10.3389/fchem.2021.705024. eCollection 2021.
Available data on the dependence of the equilibrium chemical potential of oxygen on degrees of doping, , and non-stoichiometry, , , in U O fluorite solid solutions and data on the dependence of the lattice parameter, , on the same variables are combined within a unified structural-thermodynamic model. The thermodynamic model fits experimental isotherms of the oxygen potential under the assumptions of a non-ideal mixing of the endmembers, UO, UO, UO, O, and UO, and of a significant reduction in the configurational entropy arising from short-range ordering (SRO) within cation-anion distributions. The structural model further investigates the SRO in terms of constraints on admissible values of cation coordination numbers and, building on these constraints, fits the lattice parameter as a function of , and . Linking together the thermodynamic and structural models allows predicting the lattice parameter as a function of , and the oxygen partial pressure. The model elucidates contrasting structural and thermodynamic changes due to the doping with LaO, on the one hand, and with NdO and GdO, on the other hand. An increased oxidation resistance in the case of Gd and Nd is attributed to strain effects caused by the lattice contraction due to the doping and to an increased thermodynamic cost of a further contraction required by the oxidation.
关于UO萤石固溶体中氧的平衡化学势对掺杂度、以及非化学计量比、、的依赖性的现有数据，与晶格参数对相同变量的依赖性数据，被整合到一个统一的结构 - 热力学模型中。该热力学模型在端元UO、UO、UO、O和UO非理想混合，以及阳离子 - 阴离子分布内短程有序（SRO）导致的构型熵显著降低的假设下，拟合了氧势的实验等温线。结构模型进一步根据对阳离子配位数允许值的限制来研究SRO，并基于这些限制，将晶格参数拟合为、和的函数。将热力学模型和结构模型联系起来，可以预测晶格参数作为、和氧分压的函数。该模型阐明了一方面用LaO掺杂，另一方面用NdO和GdO掺杂所导致的截然不同的结构和热力学变化。在Gd和Nd的情况下抗氧化性增强，归因于掺杂引起的晶格收缩所导致的应变效应，以及氧化所需的进一步收缩的热力学成本增加。
