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

Changes in structure and conduction type upon addition of Ir to ZnO thin films

Zn-Ir-O (Zn/Ir ≈ 1/1) thin films have been reported to be a potential p-type TCO material. It is, however, unknown whether it is possible to achieve p-type conductivity at low Ir content, and how the type and the magnitude of conductivity are affected by the film structure. To investigate the changes in properties taking place at low and moderate Ir content, this study focuses on the structure, electrical and optical properties of ZnO:Ir films with iridium concentration varying between 0.0 and 16.4 at.%. ZnO:Ir thin films were deposited on glass, Si, and Ti substrates by DC reactive magnetron co-sputtering at room temperature. Low Ir content (up to 5.1 at.%) films contain both a nano-crystalline wurtzite-type ZnO phase and an X-ray amorphous phase. The size of the crystallites is below 10 nm and the lattice parameters a and c are larger than those of pure ZnO crystal. Structural investigation showed that the film's crystallinity declines with the iridium concentration and films become completely amorphous at iridium concentrations between 7.0 and 16.0 at.%. An intense Raman band at approximately 720 cm− 1 appears upon Ir incorporation and can be ascribed to peroxide O22– ions. Measurable electrical conductivity appears together with a complete disappearance of the wurtzite-type ZnO phase. The conduction type undergoes a transition from n- to p-type in the Ir concentration range between 12.4 and 16.4 at.%. Absorption in the visible range increases linearly with the iridium concentration.VMTKC project 18, agreement No. 1.2.1.1/16/A/005; 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

ODS ferritic steels obtained from gas atomized powders through the STARS processing route: Reactive synthesis as an alternative to mechanical alloying

Oxide Dispersion Strengthened Ferritic Stainless Steels (ODS FS) are candidate materials for structural components in fusion reactors. Their ultrafine microstructure and the presence of a very stable dispersion of Y-Ti-O nanoclusters provide reasonable fracture toughness, high mechanical and creep strength, and resistance to radiation damage at the operation temperature, up to about 750 °C. An innovative route to produce ODS FS with composition Fe-14Cr-2W-0.3Ti-0.3Y2O3 (wt.%), named STARS (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), is presented. This route avoids the mechanical alloying (MA) of the elemental or prealloyed powders with yttria to dissolve the yttrium in the ferritic matrix. In this study, starting powders containing Ti and Y are obtained by gas atomization at laboratory and industrial scale. Then, a metastable Cr- and Fe- rich oxide layer is formed on the surface of the powder particles. During consolidation by HIP the metastable oxide layer at Prior Particle Boundaries (PPBs) dissociates, the oxygen diffuses towards saturated solutions or metallic Ti- and Y-rich particles, and Y-Ti-O nano-oxides (mainly Y2TiO5) precipitate in the ferritic matrix. Detailed Microstructural characterization by X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of powders and consolidated materials is presented and correlated with mechanical behaviour

The local atomic structure and thermoelectric properties of Irdoped ZnO: hybrid DFT calculations and XAS experiments

We greatly acknowledge the financial support via the ERAF Project No. 1.1.1.1/18/A/073. Calculations have been performed under the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H2020 Programme. A. C. gratefully acknowledges the technical support received from KTH-PDC. 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 CAMART2We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOx polyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O22−). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx (x = 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (μF) falls in the range of 0–0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80–89 μV K−1 slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence of S on μF in this range for two complexes with the formation of peroxide ions (O22−). We predicted also that peroxide ions O22− are characterized by the calculated phonon frequencies of 810–942 cm−1 in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculated S(μF) dependences to the atomic and electronic structure.--//--This is the preprint version of the following article: Andrei Chesnokov, Denis Gryaznov, Natalia V. Skorodumova, Eugene A. Kotomin, Andrea Zitolo, Martins Zubkins, Alexei Kuzmin, Andris Anspoks, Juris Purans; The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiment, Journal of Materials CHemistry C: Volume 14, 2021, which has been published in final form at https://pubs.rsc.org/en/content/articlelanding/2021/tc/d1tc00223f#!divAbstract This article may be used for non-commercial purposes in accordance with Royal Society of Chemistry Terms and Conditions for Sharing and Self-Archiving.ERAF Project No. 1.1.1.1/18/A/073; Project HPC-EUROPA3 (INFRAIA-2016-1-730897) under EC Research Innovation Action under H2020; 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

Analysis of extended x-ray absorption fine structure data from copper tungstate by the reverse Monte Carlo method

The static disorder and lattice dynamics of crystalline materials can be efficiently studied using reverse Monte Carlo simulations of extended x-ray absorption fine structure spectra (EXAFS). In this work we demonstrate the potentiality of this method on an example of copper tungstate CuWO4. The simultaneous analysis of the Cu K and W L3 edges EXAFS spectra allowed us to follow local structure distortion as a function of temperature

ODS ferritic steels obtained from gas atomized powders through the STARS processing route: Reactive synthesis as an alternative to mechanical alloying

Oxide Dispersion Strengthened Ferritic Stainless Steels (ODS FS) are candidate materials for structural components in fusion reactors. Their ultrafine microstructure and the presence of a very stable dispersion of Y-Ti-O nanoclusters provide reasonable fracture toughness, high mechanical and creep strength, and resistance to radiation damage at the operation temperature, up to about 750 °C. An innovative route to produce ODS FS with composition Fe-14Cr-2W-0.3Ti-0.3Y2O3 (wt.%), named STARS (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), is presented. This route avoids the mechanical alloying (MA) of the elemental or prealloyed powders with yttria to dissolve the yttrium in the ferritic matrix. In this study, starting powders containing Ti and Y are obtained by gas atomization at laboratory and industrial scale. Then, a metastable Cr- and Fe- rich oxide layer is formed on the surface of the powder particles. During consolidation by HIP the metastable oxide layer at Prior Particle Boundaries (PPBs) dissociates, the oxygen diffuses towards saturated solutions or metallic Ti- and Y-rich particles, and Y-Ti-O nano-oxides (mainly Y2TiO5) precipitate in the ferritic matrix. Detailed Microstructural characterization by X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of powders and consolidated materials is presented and correlated with mechanical behaviour