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

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

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Article number34
Journalnpj Materials Degradation
Issue number1
StatePublished - Dec 2021
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry
  • Materials Science (miscellaneous)
  • Chemistry (miscellaneous)


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