Simulation of diffusion of oxygen and uranium in uranium dioxide nanocrystals

Kupryazhkin, A. Ya.; Zhiganov, A. N.; Risovany, D.V.; Nekrassov, K.A.; Risovany, V.D.; Golovanov, V. N.

doi:10.1016/j.jnucmat.2007.03.176

Cited by 38 publications

(28 citation statements)

References 9 publications

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“…Such charts for self-diffusion of oxygen anions in UO 2 are given in several papers [18][19][20][21][22][23][24][25]. However, as it can be seen from Table 1, all the results obtained there (except [20]) have such limitations as a small number of temperature points (with a coarse step of 100-250 K) and narrow range of temperatures (only one or two points below 2200 K).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the influence of potentials and boundary conditions upon the model was not studied. Later the anion self-diffusion in nanocrystals was also studied with Walker-81 and Nekrasov-08 SPPs [22], but that work lacked segmentation of diffusion mechanisms and the aforementioned issues were not overcome. Finally, the approximation of rigid ions and pair interactions (RIPI) under periodic boundary conditions (PBC), which was used in most of the previous works, could affect the results of diffusion simulation.…”

Section: Introductionmentioning

confidence: 99%

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High-precision molecular dynamics simulation of UO2–PuO2: Anion self-diffusion in UO2

Potashnikov

Boyarchenkov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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h i g h l i g h t s" We perform MD simulation of oxygen diffusion in UO2 (up to 50 000 ions and 1 ls time)." We reached 1400 K and 10 À12 cm 2 /sec, which allowed direct comparison to experiments." S-shaped T-dependence of activation energy and k-peak of its derivative were obtained. " Continual superionic phase transition (rather than first or second order) was proved. t r a c tOur series of articles is devoted to high-precision molecular dynamics simulation of mixed actinide-oxide (MOX) fuel in the approximation of rigid ions and pair interactions (RIPI) using high-performance graphics processors (GPU). In this article we study self-diffusion mechanisms of oxygen anions in uranium dioxide (UO 2 ) with the 10 recent and widely used sets of interatomic pair potentials (SPP) under periodic (PBC) and isolated (IBC) boundary conditions. Wide range of measured diffusion coefficients (from 10 À3 cm 2 /s at melting point down to 10 À12 cm 2 /s at 1400 K) made possible a direct comparison (without extrapolation) of the simulation results with the experimental data, which have been known only at low temperatures (T < 1500 K). A highly detailed (with the temperature step of 1 K) calculation of the diffusion coefficient allowed us to plot temperature dependences of the diffusion activation energy and its derivative, both of which show a wide ($1000 K) superionic transition region confirming the broad k-peaks of heat capacity obtained by us earlier. It is shown that regardless of SPP the anion self-diffusion in model crystals without surface or artificially embedded defects goes on via exchange mechanism, rather than interstitial or vacancy mechanisms suggested by the previous works. The activation energy of exchange diffusion turned out to coincide with the anti-Frenkel defect formation energy calculated by the lattice statics.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-precision molecular dynamics simulation of UO2–PuO2: Anion self-diffusion in UO2

Potashnikov

Boyarchenkov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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“…For example, our experiments have shown that non-equilibrium cubic crystals (as in [18]) loose the original shape after 100 ps (at 2000 K) from the start; at that, not only surface atoms rearrange, but also the deeper layers. As a result, the original layering of the crystal becomes invalid, and the calculated diffusion coefficients become overestimated.…”

Section: Calculation Of the Diffusion Coefficients Of Bulk And Surfacmentioning

confidence: 89%

“…In 2008 the first attempt of calculation of cation diffusion coefficient (DC) in such nanocrystals was made [18]. The diffusion coefficients obtained for cations in the bulk were about 10 -9 -10 -7 cm 2 /s and seemed independent of interatomic potentials (Walker-81 and Nekrasov-08) and of system size (4116 and 6144 ions).…”

Section: Introductionmentioning

confidence: 99%

“…Besides, UO 2 nanocrystals of the cubic shape used there have considerable excess energy and, as shown in [19], such crystals are subject to a process of structural relaxation. This process does not affect the faster diffusion of anions (see the comparison of diffusion in the cubic and octahedral crystals [4]), however, led to a significant overestimation of cation DCs obtained in [18]. In [20] the uranium diffusion in the presence of grain boundaries was simulated.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Boyarchenkov

Potashnikov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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a b s t r a c tThis article is devoted to investigation of cation self-diffusion mechanisms, taking place in UO 2 , UO 2+x , and UO 2Àx crystals simulated under periodic (PBC) and isolated (IBC) boundary conditions using the method of molecular dynamics in the approximation of rigid ions and pair interactions. It is shown that under PBC the cations diffuse via an exchange mechanism (with the formation of Frenkel defects) with activation energy of 15-22 eV, while under IBC there is competition between the exchange and vacancy (via Schottky defects) diffusion mechanisms, which give the effective activation energy of 11-13 eV near the melting temperature of the simulated UO 2.00 nanocrystals. Vacancy diffusion with lower activation energy of 6-7 eV was dominant in the non-stoichiometric crystals UO 2.10 , UO 2.15 and UO 1.85 . Observations showed that a cation vacancy is accompanied by different number of anion vacancies depending on the deviation from stoichiometry: no vacancies in UO 2.15 , single vacancy in UO 2.00 and four vacancies in UO 1.85 . The corresponding law of mass action formulas derived within the Lidiard-Matzke model allowed explaining the obtained activation energies and predicting a change in the activation energy within the temperature range of the superionic phase transition. The diffusion of cations on the surface of nanocrystals had activation energy of 3.1-3.6 eV.

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Intrinsic Defects: Diffusion

2009

Charged Semiconductor Defects

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Simulation of diffusion of oxygen and uranium in uranium dioxide nanocrystals

Cited by 38 publications

References 9 publications

High-precision molecular dynamics simulation of UO2–PuO2: Anion self-diffusion in UO2

High-precision molecular dynamics simulation of UO2–PuO2: Anion self-diffusion in UO2

Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics

Intrinsic Defects: Diffusion

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