Molecular Dynamics Simulation of Oxygen Diffusion in (PuxTh1−x)O2 Crystals


Seitov D.D. Nekrasov K.A. Ustiuzhanin D.A. Boyarchenkov A.S. Kuznetsova Y.A. Pitskhelaury S.S. Gupta S.K.
November 2025Multidisciplinary Digital Publishing Institute (MDPI)

Crystals
2025#15Issue 11

Oxygen diffusion in (PuxTh1−x)O2 mixed oxide crystals was investigated using molecular dynamics simulation. The model systems were isolated nanocrystals of 5460 and 15,960 particles, featuring a free surface. The oxygen diffusion coefficient D increased with decreasing thorium content, in accordance with the decrease in the melting temperature of (PuxTh1−x)O2 as x varied from 0 to 1. The temperature dependences D(T) exhibited non-linearity in the Arrhenius coordinates lnD = f(1/kT). The three linear segments of the plots corresponded to the superionic state, a transitional region, and the low-temperature crystalline phase. The transitional region was characterized by maximum values of the effective diffusion activation energy ED(PuO2) = 3.47 eV, ED(ThO2) = 5.24 eV and a complex collective mechanism of oxygen migration, which involved the displacement of anions into interstitial sites. At lower temperatures, an interstitialcy mechanism of oxygen diffusion was observed. The temperature dependence of D(PuO2) showed quantitative agreement with low-temperature experimental data.

migration mechanisms , molecular dynamics , oxygen diffusion , plutonium dioxide , thorium dioxide

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Department of Nuclear Physics, New Materials, and Technology, School of Physics and Technology, L.N. Gumilyov Eurasian National University, 2, Satbayev Str., Astana, 010008, Kazakhstan
Institute of Physics and Technology, Ural Federal University Named After the First President of Russia B.N. Yeltsin, 21, Mira Str, Ekaterinburg, 620002, Russian Federation
OOO “VisionLabs”, Podsosensky Lane, Bld. 23, Str. 3, Moscow, 101000, Russian Federation
Computational Materials and Nanoscience Group, Department of Physics and Electronics, St. Xavier’s College, P.B. 4168, Navrangpura, Ahmedabad, 380009, India

Department of Nuclear Physics
Institute of Physics and Technology
OOO “VisionLabs”
Computational Materials and Nanoscience Group

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