Investigation of thermally induced anion disorder in fluorites using neutron scattering techniques

Hutchings, M. T.; Clausen, K.N.; Dickens, Michael; Hayes, W.; Kjems, Jørgen; Schnabel, Peter; Smith, Chris

doi:10.1088/0022-3719/17/22/011

Cited by 148 publications

(104 citation statements)

References 50 publications

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“…This mechanism is often called exchange, although some authors distinguish direct exchange of two ions and ring substitution of more than two ions. Exchange diffusion probably occurs in natural crystals, which is supported by experimental observation of short-lived anti-Frenkel pair formation in UO 2 and similar crystals CaF 2 , PbF 2 and SrCl 2 of fluorite structure [48,3].…”

Section: Quasi-infinite Crystals Under Pbcsupporting

confidence: 53%

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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Section: Quasi-infinite Crystals Under Pbcsupporting

confidence: 53%

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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“…Vacancy concentration can be directly measured in a wide temperature range by technique of high-temperature diffraction and inelastic neutron scattering (see, e.g., [43]), which allows to determine the energy of AFD formation. Note that interpretation of available data remains ambiguous due to the complexity of measurement conduction and analysis, as well as significant statistical errors.…”

Section: Lattice Statics Calculation Of Defect Formation Energiesmentioning

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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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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“…The SrCl 2 has the cubic fluorite structure with the space group of Fm3m [13]. Its lattice constant of the face-centred cube is 0.70 nm at 293 K and its melting temperature is 1146 K [13,14].…”

Section: Crystal Structure and Experimental Aspectsmentioning

confidence: 99%

“…Its lattice constant of the face-centred cube is 0.70 nm at 293 K and its melting temperature is 1146 K [13,14]. It may be viewed as a simple cubic array of anions (chlorine ions), with alternate cube centres occupied by cations (strontium ions).…”

Section: Crystal Structure and Experimental Aspectsmentioning

confidence: 99%

Electron Magnetic Resonance of Eu²⁺in SrCl₂:Eu Single Crystal

Lee¹,

Yeom²,

Kim³

2012

Journal of Magnetics

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Investigation of thermally induced anion disorder in fluorites using neutron scattering techniques

Cited by 148 publications

References 50 publications

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

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

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

Electron Magnetic Resonance of Eu²⁺in SrCl₂:Eu Single Crystal

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Investigation of thermally induced anion disorder in fluorites using neutron scattering techniques

Cited by 148 publications

References 50 publications

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

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

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

Electron Magnetic Resonance of Eu2+in SrCl2:Eu Single Crystal

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Electron Magnetic Resonance of Eu²⁺in SrCl₂:Eu Single Crystal