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

Marcial, J.; Zhang, Yuanpeng; Zhao, X.; Xu, H.; Mesbah, A.; Nienhuis, E. T.; Szenknect, S.; Neuefeind, Joerg C.; Lin, J.; Qi, L.; Migdisov, A. A.; Ewing, R. C.; Dacheux, N.; McCloy, J. S.; Guo, X.

doi:10.1038/s41529-021-00179-0

DOE OSTI · 1817570

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

Marcial, J.·Zhang, Yuanpeng·Zhao, X.·Xu, H.·Mesbah, A.·Nienhuis, E. T.·Szenknect, S.·Neuefeind, Joerg C.·Lin, J.·Qi, L.·Migdisov, A. A.·Ewing, R. C.·Dacheux, N.·McCloy, J. S.·Guo, X.

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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 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.

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Marcial, J., Zhang, Yuanpeng, Zhao, X., Xu, H., Mesbah, A., Nienhuis, E. T., Szenknect, S., Neuefeind, Joerg C., Lin, J., Qi, L., Migdisov, A. A., Ewing, R. C., Dacheux, N., McCloy, J. S., Guo, X.. 2021-06-18. Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions. https://doi.org/10.1038/s41529-021-00179-0

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