Kinetics of the electronic center annealing in Al2O3 crystals

Authors are greatly indebted to A. Ch. Lushchik, V. Kortov, M. Izerrouken and R.Vila for stimulating discussions. This work has been carried out within the framework of the Eurofusion Consortium and has received funding from the Euroatom research and training programme 2014–2018 under grant agreement No 633053 . The views and opinions expressed herein do not necessarily reflect those of the European Commission. The calculations were performed using facilities of the Stuttgart Supercomputer Center (project DEFTD 12939 ).The experimental annealing kinetics of the primary electronic F, F+ centers and dimer F2 centers observed in Al2O3 produced under neutron irradiation were carefully analyzed. The developed theory takes into account the interstitial ion diffusion and recombination with immobile F-type and F2-centers, as well as mutual sequential transformation with temperature of three types of experimentally observed dimer centers which differ by net charges (0, +1, +2) with respect to the host crystalline sites. The relative initial concentrations of three types of F2 electronic defects before annealing are obtained, along with energy barriers between their ground states as well as the relaxation energies.Euroatom 2014–2018 agreement No 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Kinetics of the electronic center annealing in Al2O3 crystals

Authors are greatly indebted to A. Ch. Lushchik, V. Kortov, M. Izerrouken and R.Vila for stimulating discussions. This work has been carried out within the framework of the Eurofusion Consortium and has received funding from the Euroatom research and training programme 2014–2018 under grant agreement No 633053 . The views and opinions expressed herein do not necessarily reflect those of the European Commission. The calculations were performed using facilities of the Stuttgart Supercomputer Center (project DEFTD 12939 ).The experimental annealing kinetics of the primary electronic F, F+ centers and dimer F2 centers observed in Al2O3 produced under neutron irradiation were carefully analyzed. The developed theory takes into account the interstitial ion diffusion and recombination with immobile F-type and F2-centers, as well as mutual sequential transformation with temperature of three types of experimentally observed dimer centers which differ by net charges (0, +1, +2) with respect to the host crystalline sites. The relative initial concentrations of three types of F2 electronic defects before annealing are obtained, along with energy barriers between their ground states as well as the relaxation energies.Euroatom 2014–2018 agreement No 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Kinetics of dimer F2 type center annealing in MgF2 crystals

Authors are greatly indebted to V. Lisitsyn, A. Ch. Lushchik and R.Vila for stimulating discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The calculations were performed using facilities of the Stuttgart Supercomputer Center (project DEFTD 12939).In this paper, we analyzed experimental annealing kinetics of the primary electronic F centers and dimer F2 centers observed in MgF2 at higher radiation doses and temperatures. The developed phenomenological theory takes into account the interstitial ion diffusion and recombination with the F2-centers, as well as mutual sequential transformation with temperature growth of three types of experimentally observed dimer centers: F2(1), F2(2), F2(3) (which differ tentatively by charges (0, +1, +2) with respect to the host crystalline sites). The results of the electron, neutron and ion irradiation are compared. As the result, the relative initial concentrations of three types of F2 electronic defects before annealing are obtained, along with energy barriers between their ground states as well as the relaxation energies.European Union’s Horizon 2020 agreement number 633053; Stuttgart Supercomputer Center project DEFTD 12939; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Kinetic Monte Carlo modeling of Y2O3 nano-cluster formation in radiation resistant matrices

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.As known, Y2O3 nano-clusters considerably increase radiation resistance of reactor construction materials. To model the nano-cluster formation kinetics, we propose the simplest possible mathematical model and perform kinetic Monte Carlo (KMC) simulations. We extended the KMC simulated results to the experimentally relevant times using autoregressive integrated moving average forecasting. Within the model, we have studied prototypical attractive interaction energies and particle concentrations, and compared the simulations with experiments. We have observed the standard Lifshitz-Slyozov-Wagner (LSW) theory, predicting the average cluster radius growth with time, , with in the long-time limit, for weak (0.1 eV) mutual particle attraction. However, the respective cluster growth rates in these KMC simulations are overestimated compared to the experiments. The best agreement with experiment is obtained for a medium (0.3 eV) and strong (0.5 eV) attractions, when nano-cluster formation occurs during intermediate asymptotic time scale, where power order p ranges from 5 to 7.6 depending on interaction, without reaching actually the LSW long-time limit. Such a stronger interaction leads also to a more compact {110}–faceted nano-clusters.EUROfusion Consortium; Euratom research and training programme 2014-2018 under grant agreement No 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Peculiarities of the diffusion-controlled radiation defect accumulation kinetics under high fluencies

We are grateful to A. Lushchik and E. Shablonin for numerous and valuable discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.Theory is developed for kinetics of the diffusion-controlled radiation defect accumulation in crystalline solids under high fluencies taking into account recently observed correlation between the defect diffusion energy and pre-exponential (known as the Meyer-Neldel rule in chemical kinetics) and their dependence on the radiation fluence (Kotomin et al., J Phys Chem A 122 (2018) 28). The predicted accumulation kinetics could be applied to all kinds of solids. It considerably differs from the commonly used, in particular, suggesting that concentration growth at high fluencies could be nonmonotonous and the saturation defect concentrations independent on the temperature.EUROfusion Consortium Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Distinctive features of diffusion-controlled radiation defect recombination in stoichiometric magnesium aluminate spinel single crystals and transparent polycrystalline ceramics

This work has been performed within the framework of the EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02 “Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion application”. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Research of A.L, E.F.,, V.S and E.S has been partly supported by the Estonian Research Council grant (PUT PRG619); has been also carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.MgAl2O4 spinel is important optical material for harsh radiation environment and other important applications. The kinetics of thermal annealing of the basic electron (F, F+) and hole (V) centers in stoichiometric MgAl2O4 spinel irradiated by fast neutrons and protons is analyzed in terms of diffusion-controlled bimolecular reactions. Properties of MgAl2O4 single crystals and optical polycrystalline ceramics are compared. It is demonstrated that both transparent ceramics and single crystals, as well as different types of irradiation show qualitatively similar kinetics, but the effective migration energy Ea and pre-exponent D0 are strongly correlated. Such correlation is discussed in terms of the so-called Meyer-Neldel rule known in chemical kinetics of condensed matter. The results for the irradiated spinel are compared with those for sapphire, MgO and other radiation-resistant materials.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Two-Species Annihilation with Drift: A Model with Continuous Concentration-Decay Exponents

We propose a model for diffusion-limited annihilation of two species, $A+B\to A$ or $B$, where the motion of the particles is subject to a drift. For equal initial concentrations of the two species, the density follows a power-law decay for large times. However, the decay exponent varies continuously as a function of the probability of which particle, the hopping one or the target, survives in the reaction. These results suggest that diffusion-limited reactions subject to drift do not fall into a limited number of universality classes.Comment: 10 pages, tex, 3 figures, also available upon reques

Exact Solutions of Anisotropic Diffusion-Limited Reactions with Coagulation and Annihilation

We report exact results for one-dimensional reaction-diffusion models A+A -> inert, A+A -> A, and A+B -> inert, where in the latter case like particles coagulate on encounters and move as clusters. Our study emphasized anisotropy of hopping rates; no changes in universal properties were found, due to anisotropy, in all three reactions. The method of solution employed mapping onto a model of coagulating positive integer charges. The dynamical rules were synchronous, cellular-automaton type. All the asymptotic large-time results for particle densities were consistent, in the framework of universality, with other model results with different dynamical rules, when available in the literature.Comment: 28 pages in plain TeX + 2 PostScript figure

Anisotropic Diffusion-Limited Reactions with Coagulation and Annihilation

One-dimensional reaction-diffusion models A+A -> 0, A+A -> A, and $A+B -> 0, where in the latter case like particles coagulate on encounters and move as clusters, are solved exactly with anisotropic hopping rates and assuming synchronous dynamics. Asymptotic large-time results for particle densities are derived and discussed in the framework of universality.Comment: 13 pages in plain Te