Local structural studies of Fe-based superconductors

In the framework of high temperature superconductors, the Fe-based systems are the rst magnetic materials that exhibit a critical temperature above 50 K. These systems are characterized by strong interplay between electronic, spin and lattice degrees of freedom and the macroscopic functional properties arise from the competitions between them. All the theoretically and experimental results point out on the diff iculty to separate the effects of disorder, doping and magnetism on the superconducting properties. The presence of multiple bands crossing the Fermi level makes the electronic structure very sensitive to the structural details, particulary to the changes on the local atomic arrangement in the Fe-Pn/Ch slabs. The aim of this work is to study the local structure and discuss possible implications on the electronic properties in the Fe-based superconductors. This has important implications, both in theoretical and in practical terms: a close relationship between structure and superconductivity, direct or indirect, places constraints on both the theoretical understanding of the pairing interaction and the promise of superconductors with higher TC values. The proposed sensitivity of electronic structure and/or magnetic interactions to the details of the internal structure of the Fe-As layers is likely relevant to unraveling this puzzle

Microwave-assisted synthesis and electrochemical evaluation of VO2 (B) nanostructures

Understanding how intercalation materials change during electrochemical operation is paramount to optimizing their behaviour and function and in situ characterization methods allow us to observe these changes without sample destruction. Here we first report the improved intercalation properties of bronze phase vanadium dioxide VO2 (B) prepared by a microwave-assisted route which exhibits a larger electrochemical capacity (232 mAh g-1) compared with VO2 (B) prepared by a solvothermal route (197 mAh g-1). These electrochemical differences have also been followed using in situ X-ray absorption spectroscopy allowing us to follow oxidation state changes as they occur during battery operation

Decoupling the effect of vacancies and electropositive cations on the anionic redox processes in Na based P2-type layered oxides

The activation of anionic redox couple is recognized as one of the best way to increase the energy density of positive electrode materials in both Li and Na-ion batteries. However, for such hope, to materialize a better understanding of the parameters governing the activation, reversibility and efficiency of the anionic redox in NaMO2 layered compounds is still sorely needed. Herein, we report a new P2–Na0.63[□0.036Mg0.143Mn0.820]O2 compound that combines vacancies and Mg doping as well-known sources for anionic redox activation and benchmark its electrochemical performances against P2–Na0.72[Mg0.31Mn0.69]O2. We found that vacancies and Mg doping trigger independently anionic redox processes that differ in terms of redox voltage and reversibility. The one associated to vacancies occurs at the lowest potential and is irreversible. Moreover, we evidenced by monitoring the structural evolution of the pristine phase during cycling the benefice of anionic processes in ensuring the stabilization of P2-type structure at high voltage over a wide range in Na content. These findings highlight the importance of the anionic redox process origin (e.g. vacancies vs. highly electropositive cations) in governing the material electrochemical properties, while providing a new way to efficiently stabilize, without capacity loss, the P2-type structure through the charge process in non A-rich compounds

Impact of Solution Chemistry on Growth and Structural Features of Mo-Substituted Spinel Iron Oxides

International audienceThe effect of crystallizing solution chemistry on the chemistry of subsequently as-grown materials was investigated for Mo-substituted iron oxides prepared by thermally activated co-precipitation. In the presence of Mo ions, we find that varying the oxidation state of the iron precursor from Fe(II) to Fe(III) causes a progressive loss of atomic long-range order with the stabilization of 2–4 nm particles for the sample prepared with Fe(III). The oxidation state of the Fe precursor also affects the distribution of Fe and Mo cations within the spinel structure. Increasing the Fe precursor oxidation state gives decreased Fe-ion occupation and increased Mo-ion occupation of tetrahedral sites, as revealed by the extended X-ray absorption fine structure. The stabilization of Mo within tetrahedral sites appears to be unexpected, considering the octahedral preferred coordination number of Mo(VI). The analysis of the atomic structure of the sample prepared with Fe(III) indicates a local ordering of vacancies and that the occupation of tetrahedral sites by Mo induces a contraction of the interatomic distances within the polyhedra as compared to Fe atoms. Moreover, the occupancy of Mo into the thermodynamic site preference of a Mo dopant in Fe2O3 assessed by density functional theory calculations points to a stronger preference for Mo substitution at octahedral sites. Hence, we suggest that the synthetized compound is thermodynamically metastable, that is, kinetically trapped. Such a state is suggested to be a consequence of the tetrahedral site occupation by Mo ions. The population of these sites, known to be reactive sites enabling particle growth, is concomitant with the stabilization of very small particles. We confirmed our hypothesis by using a blank experiment without Mo ions, further supporting the impact of tetrahedral Mo ions on the growth of iron oxide nanoparticles. Our findings provide new insights into the relationships between the Fe-chemistry of the crystallizing solution and the structural features of the as-grown Mo-substituted Fe-oxide materials

Efficient artificial mineralization route to decontaminate Arsenic(III) polluted water -the Tooeleite Way

Increasing exposure to arsenic (As) contaminated ground water is a great threat to humanity. Suitable technology for As immobilization and removal from water, especially for As(III) than As(V), is not available yet. However, it is known that As(III) is more toxic than As(V) and most groundwater aquifers, particularly the Gangetic basin in India, is alarmingly contaminated with it. In search of a viable solution here, we took a cue from the natural mineralization of Tooeleite, a mineral containing Fe(III) and As(III)ions, grown under acidic condition, in presence of SO42- ions. Complying to this natural process, we could grow and separate Tooeleite-like templates from Fe(III) and As(III) containing water at overall circumneutral pH and in absence of SO42- ions by using highly polar Zn-only ends of wurtzite ZnS nanorods as insoluble nano-acidic-surfaces. The central idea here is to exploit these insoluble nano-acidic-surfaces (called as INAS in the manuscript) as nucleation centres for Tooeleite growth while keeping the overall pH of the aqueous media neutral. Therefore, we propose a novel method of artificial mineralization of As(III) by mimicking a natural process at nanoscale

Anionic Redox Activity in a Newly Zn-Doped Sodium Layered Oxide P2-Na2/3 Mn1− y Zn y O2 (0 < y < 0.23)

The revival of the Na‐ion battery concept has prompted intense research activities toward new sustainable Na‐based insertion compounds and their implementation in full Na‐ion cells. Efforts are parted between Na‐based polyanionic and layered compounds. For the latter, there has been a specific focus on Na‐deficient layered phases that show cationic and anionic redox activity similar to a Na0.67Mn0.72Mg0.28O2 phase. Herein, a new alkali‐deficient P2‐Na2/3Mn7/9Zn2/9O2 phase using a more electronegative element (Zn) than Mg is reported. Like its Mg counterpart, this phase shows anionic redox activity and no O2 release despite evidence of cationic migration. Density functional theory (DFT) calculations show that it is the presence of an oxygen nonbonding state that triggers the anionic redox activity in this material. The phase delivers a reversible capacity of 200 mAh g−1 in Na‐half cells with such a value be reduced to 140 mAh g−1 in full Na‐ion cells which additionally shows capacity decay upon cycling. These findings establish Na‐deficient layered oxides as a promising platform to further explore the underlying science behind O2 release in insertion compounds based on anionic redox activity

The Director’s Method in Contemporary Visual Effects Film: The Influence of Digital Effects on Film Directing

The director’ s method – meant as the organisation of the filmmaking process – is usually characterised by common procedures such as work on the script, shot design and the actors’ performance. For films involving a large-scale use of digital effects, directors consistently approach such procedures with a particular attitude dictated by the digital pipeline, the step-by-step technical procedure through which computer-generated images are created. In light of this, the use of digital effects might influence the director’s method. This thesis aims to define what is considered to be a consensual methodological approach to direct films with no or few digital effects and then compares this approach to when such effects are conspicuously involved. This analysis is conducted through interviews with working directors, visual effects companies and practitioners, and integrated with the current literature. The frame of the research is represented by a large spectrum of contemporary films produced in western countries and which involve digital effects at different scales and complexity but always in interaction with live-action. The research focuses on commercial films and excludes computer-animated and experimental films. The research is intended to address an area in production studies which is overlooked. In fact, although the existent literature examines both digital effects and film directing as distinct elements, there is to date no detailed analysis on the influence that the former has on the latter. In light of this, this dissertation seeks to fill a gap in production studies. The research looks to argue that the director’s method has been changed by the advent of digital effects; it describes a common workflow for digital effects film and notes the differences between this method and the method applied when digital effects are not involved. This is of significant importance for a film industry which is heavily dependent on such effects, as the analysis on contemporary filmmaking reveal

Unraveling the Charge Storage Mechanism of Ti3C2Tx MXene Electrode in Acidic Electrolyte

Two-dimensional Ti3C2Tx MXenes have been extensively studied as pseudocapacitive electrode materials. This Letter aims at providing further insights into the charge storage mechanism of the Ti3C2Tx MXene electrode in the acidic electrolyte by combining experimental and simulation approaches. Our results show that the presence of H2O molecules between the MXene layers plays a critical role in the pseudocapacitive behavior, providing a pathway for proton transport to activate the redox reaction of the Ti atoms. Also, thermal annealing of the samples at different temperatures suggests that the presence of the confined H2O molecules is mainly controlled by the surface termination groups. These findings pave the way for alternative strategies to enhance the high-rate performance of MXenes electrodes by optimizing their surface termination groups

Report on CERIC's Expert Group on Batteries

The report is a part of the efforts of CERIC-ERIC, a distributed research infrastructure in the field of materials characterisation and modification, to produce its Research and Infrastructure Roadmap. General Assembly has in 2019 approved a pilot action on Batteries, in order to identify the bottlenecks and needs for upgrades of CERIC-ERIC in this domain. To this end, an expert group consisting of Antonella Iadecola, Lorenzo Stievano and Benedetto Bozzini was contracted and the group submitted their report May 18th 2020. The activity is supported by the project ACCELERATE, co-funded by the European Union Framework Programme for Research and Innovation Horizon 2020 under grant agreement 731112 and coordinated by CERIC

Li deinsertion mechanism and Jahn–Teller distortion in LiFe0.75Mn0.25PO4: an operando x-ray absorption spectroscopy investigation

International audienceThe electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by operando x-ray absorption spectroscopy (XAS) at both Fe and Mn K edges. XAS data were interpreted using an innovating chemometric approach, allowing the detailed reconstruction of the rather complicated reaction mechanism involving two different metal centres. In this way it was possible to precisely describe the Jahn–Teller effect occurring upon oxidation of the manganese centres. The thorough comprehension of the electrochemical mechanism is of high interest for studying the effect of lithium extraction in the olivine structure in the presence of Mn, which is known to partially hamper the complete lithiation of such mixed metal systems