Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions

J. Marcial , Y. Zhang , X. Zhao , H. Xu , Adel Mesbah (1) , E. Nienhuis , S. Szenknect , J. Neuefeind , J. Lin , L. Qi , A. Migdisov , R. Ewing , N. Dacheux , J. Mccloy , X. Guo

1 LIME - Interfaces de Matériaux en Evolution

Abstract Non-ideal thermodynamics of solid solutions can greatly impact materials degradation behavior. We have investigated an actinide silicate solid solution system (USiO 4 –ThSiO 4 ), 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 5 f –O 2 p 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.

Domaines: Chimie

J. Marcial, Y. Zhang, X. Zhao, H. Xu, Adel Mesbah, et al.. Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions. npj Materials Degradation, 2021, 5 (1), ⟨10.1038/s41529-021-00179-0⟩. ⟨hal-03396300⟩