Non-ideal thermodynamics of solid solutions can greatly impact materials degradation behavior. We have investigated an actinide silicate solid solution system (USiO₄–ThSiO₄), demonstrating that thermodynamic non-ideality follows a distinctive, atomic-scale disordering process, which is usually considered as a random distribution. Neutron total scattering implemented by pair distribution function analysis confirmed a random distribution model for U and Th in first three coordination shells; however, a machine-learning algorithm suggested heterogeneous U and Th clusters at nanoscale (~2 nm). The local disorder and nanosized heterogeneous is an example of the non-ideality of mixing that has an electronic origin. Partial covalency from the U/Th 5f–O 2p hybridization promotes electron transfer during mixing and leads to local polyhedral distortions. The electronic origin accounts for the strong non-ideality in thermodynamic parameters that extends the stability field of the actinide silicates in nature and under typical nuclear waste repository conditions.

固溶体的非理想热力学会极大地影响材料的降解行为。我们研究了锕系硅酸盐固溶体系统 (USIO ₄ –ThSiO ₄ )，证明热力学非理想性遵循独特的原子级无序过程，这通常被认为是随机分布。通过对分布函数分析实现的中子总散射证实了前三个配位壳中 U 和 Th 的随机分布模型；然而，机器学习算法提出了纳米级（~2 nm）的异构 U 和 Th 簇。局部无序和纳米级异质是具有电子起源的非理想混合的一个例子。来自 U/Th 5 f –O 2 的部分共价p杂化在混合过程中促进电子转移并导致局部多面体扭曲。电子起源解释了热力学参数的强烈非理想性，这些参数扩展了自然界和典型核废料储存库条件下锕系硅酸盐的稳定性场。