Study of the thermochromic phase transition in CuMo1−xWxO4 solid solutions at the W L3-edge by resonant X-ray emission spectroscopy

This is the peer reviewed version of the following article: I. Pudza, A. Kalinko, A. Cintins, A. Kuzmin, Acta Mater. 205 (2021) 116581, which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S1359645420310181 This article may be used for non-commercial purposes in accordance with Elsevier Terrms and Conditions for Self-Archiving.Polycrystalline CuMo1−xWxO4 solid solutions were studied by resonant X-ray emission spectroscopy (RXES) at the W L3-edge to follow a variation of the tungsten local atomic and electronic structures across thermochromic phase transition as a function of sample composition and temperature. The experimental results were interpreted using ab initio calculations. The crystal-field splitting parameter Δ for the 5d(W)-states was obtained from the analysis of the RXES plane and was used to evaluate the coordination of tungsten atoms. Temperature-dependent RXES measurements were successfully employed to determine the hysteretic behaviour of the structural phase transition between the α and γ phases in CuMo1−xWxO4 solid solutions on cooling and heating, even at low (x 0.15 in the whole studied temperature range (90-420 K), whereas their coordination changes from tetrahedral to octahedral upon cooling for smaller (x ≤ 0.15) tungsten content. Nevertheless, some amount of tungsten ions was found to co-exists in the octahedral environment at room temperature for x < 0.15. The obtained results correlate well with the color change in these solid solutions.Financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2019/1 realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. The used infrastructure of the von Hamos spectrometer was realized in the frame of projects FKZ 05K13UK1 and FKZ 05K14PP1. The experiment at the PETRA III synchrotron was performed within the project No. I-20180615 EC.The synchrotron experiments have been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. The experiment at the Elettra synchrotron was performed within the project No. 20150303. 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 CAMART2

Low temperature X-ray absorption spectroscopy study of CuMoO4 and CuMo0.90W0.10O4 using reverse Monte-Carlo method

Reversible thermochromic phase transition between α- and γ-phases was studied in CuMoO4 and CuMo0.90W0.10O4 using X-ray absorption spectroscopy in the temperature range of 10–300 K. Reverse Monte Carlo modelling with evolutionary algorithm approach at several absorption edges simultaneously was applied to extract structural information encoded in the experimental EXAFS spectra. The obtained results show that an addition of 10 mol% of tungsten to CuMoO4 induces local distortions in the structure and stabilizes the γ-phase, leading to an increase of the phase transition temperature by ~50–100 K.This work was supported by Scientific Research Project for Students and Young Researchers Nr. SJZ/2017/5 realized at the Institute of Solid State Physics, University of Latvia . The experiment at HASYLAB/ DESY was performed within the project I- 20160149 EC . The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020; 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

X-ray absorption near edge spectroscopy of thermochromic phase transition in CuMoO4

Thermochromic phase transition was studied in CuMoO4 using the Cu and Mo K-edge x-ray absorption spec-troscopy in the temperature range of 10-300 K. The hysteretic behavior has been evidenced from the tempera-ture dependence of the pre-edge shoulder intensity at the Mo K-edge, indicating that the transition from brown-ish-red γ-CuMoO4 to green α-CuMoO4 occurs in the temperature range of 230-280 K upon heating, whereas the α-to-γ transition occurs between 200 and 120 K upon cooling. Such behavior of the pre-edge shoulder at the Mo K-edge correlates with the change of molybdenum coordination between distorted tetrahedral in α-CuMoO4 and distorted octahedral in γ-CuMoO4. This result has been supported by ab initio full-multiple-scattering x-ray ab-sorption near edge structure (XANES) calculations.Financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2017/5 realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. The experiment at HASYLAB/DESY was performed within the project I-20160149 EC; 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

Neural Network Approach for Characterizing Structural Transformations by X-Ray Absorption Fine Structure Spectroscopy

AIF acknowledge support by the US Department of Energy, Office of Basic Energy Sciences under Grant No. DE-FG02 03ER15476. AIF acknowledges support by the Laboratory Directed Research and Development Program through LDRD 18-047 of Brookhaven National Laboratory under U.S. Department of Energy Contract No. DE-SC0012704 for initiating his research in machine learning methods. The help of the beamline staff at ELETTRA (project 20160412) synchrotron radiation facility is acknowledged. RMC-EXAFS and MD-EXAFS simulations were performed on the LASC cluster-type computer at Institute of Solid State Physics of the University of Latvia.The knowledge of the coordination environment around various atomic species in many functional materials provides a key for explaining their properties and working mechanisms. Many structural motifs and their transformations are difficult to detect and quantify in the process of work (operando conditions), due to their local nature, small changes, low dimensionality of the material, and/or extreme conditions. Here we use an artificial neural network approach to extract the information on the local structure and its in situ changes directly from the x-ray absorption fine structure spectra. We illustrate this capability by extracting the radial distribution function (RDF) of atoms in ferritic and austenitic phases of bulk iron across the temperature-induced transition. Integration of RDFs allows us to quantify the changes in the iron coordination and material density, and to observe the transition from a body-centered to a face-centered cubic arrangement of iron atoms. This method is attractive for a broad range of materials and experimental conditions.Laboratory Directed Research and Development LDRD 18-047; U.S. Department of Energy DE-FG02 03ER15476; Brookhaven National Laboratory DE-SC0012704; 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

Understanding of conversion process of magnetron deposited thin films of amorphous ReOx to crystalline ReO3 upon thermal annealing

Financial support was provided by ERAF Project Nr. 1.1.1.1/18/A/073. Parts of this research were carried out at PETRA-III P64 beamline at DESY, a member of the Helmholtz Association (HGF). The synchrotron experiments have been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON2020.Thin films of rhenium trioxide (ReO3) were produced by reactive DC magnetron sputtering from metallic rhenium target followed by annealing in the air in the range of temperatures from 200C to 350C. Nanocrystalline single-phase ReO3 films were obtained upon annealing at about 250C. The thin films appear bright red in reflected light and blue-green in transmitted light, thus showing an optical transparency window in the spectral range of 475-525 nm. The film exhibits high conductivity, evidenced by macro- and nano-scale conductivity measurements. The long-range and local atomic structures of the films were studied in detail by structural methods as X-ray diffraction and X-ray absorption spectroscopy. The oxidation state (6+) of rhenium was confirmed by X-ray photoemission and X-ray absorption spectroscopies. The nanocrystalline morphology of the annealed films was evidenced by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The obtained results allowed us to propose the mechanism of rhenium oxide conversion from the initially amorphous ReOx phase to cubic ReO3.ERAF 1.1.1.1/18/A/073; CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON2020; 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

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

Probing the Thermochromic Phase Transition in CuMoO4\mathrm{CuMoO_{4}} by EXAFS Spectroscopy

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Mo K-edge is used to follow the thermochromic γ-to-α phase transition in copper molybdate (CuMoO4). The temperature dependence (10–300 K) of the radial distribution function (RDF) for the Mo–O atom pairs in the first coordination shell of molybdenum atoms is reconstructed by the regularization-like method from the experimental EXAFS spectra. The analysis of the RDFs suggests that the transition occurs gradually within the two-phase coexistence range of 225–275 K. The local environment of molybdenum atoms transforms upon the γ-to-α phase transition from strongly distorted octahedral to less distorted tetrahedral coordination

The influence of Zn2+Zn^{2+} ions on the local structure and thermochromic properties of Cu1−xZnxMoO4Cu_{1-x}Zn_{x}MoO_{4} solid solutions

The influence of zinc ions on the thermochromic properties of polycrystalline $Cu_{1-x}Zn_{x}MoO_{4}$ ($$=0.10,0.50, 0.90) solid solutions was studied by X-ray absorption spectroscopy at the Cu, Zn and Mo K-edges. Detailed structural information on the local environment of metal ions was obtained from the simultaneous analysis of EXAFS spectra measured at three metal absorption edges using the reverse Monte Carlo method. Thermochromic phase transition with the hysteretic behaviour between and phases was observed in Cu$_{0.90}$Zn$_{0.10}$MoO$_4$ solid solution. It was found that the local environment of molybdenum ions is most susceptible to the substitution of copper for zinc and, upon cooling, transforms from tetrahedral MoO$_4$ to distorted octahedral MoO$_6$

The influence of Zn2+ ions on the local structure and thermochromic properties of Cu1-xZnxMoO4 solid solutions

I. P., A. K. and A. K. would like to thank the support of the Latvian Council of Science project No. lzp-2019/1-0071. I.P. acknowledges the L‘OREAL Baltic “For Women In Science” Program with the support of the Latvian National Commission for UNESCO and the Latvian Academy of Sciences. The experiment at the PETRA III synchrotron was performed within project No. I-20190277 EC. The synchrotron experiments have been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. 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 CAMART2.The influence of zinc ions on the thermochromic properties of polycrystalline CuZnMoO (=0.10, 0.50, 0.90) solid solutions was studied by X-ray absorption spectroscopy at the Cu, Zn and Mo K-edges. Detailed structural information on the local environment of metal ions was obtained from the simultaneous analysis of EXAFS spectra measured at three metal absorption edges using the reverse Monte Carlo method. Thermochromic phase transition with the hysteretic behaviour between and phases was observed in Cu0.90Zn0.10MoO solid solution. It was found that the local environment of molybdenum ions is most susceptible to the substitution of copper for zinc and, upon cooling, transforms from tetrahedral MoO to distorted octahedral MoO. ---- / / / ---- This is the preprint version of the following article:Inga Pudza, Andris Anspoks, Arturs Cintins, Aleksandr Kalinko, Edmund Welter, Alexei Kuzmin, The influence of Zn2+ ions on the local structure and thermochromic properties of Cu1-xZnxMoO4 solid solutions, Materials Today Communications, Volume 28 (2021), 102607, DOI https://doi.org/10.1016/j.mtcomm.2021.102607, which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S2352492821005997.Latvian Council of Science project No. lzp-2019/1-0071; L‘OREAL Baltic “For Women In Science” Program with the support of the Latvian National Commission for UNESCO and the Latvian Academy of Sciences; project No. I-20190277 EC; project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020; 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 CAMART2