Short-range chemical environment versus long-range chemical homogeneity analyses in high-entropy transition metal AlB2-type diboride solid solutions

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Anisotropic Thermal Expansion in High-Entropy Multicomponent Alb2-Type Diboride Solid Solutions

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10−6 to 6.9 x 10−6 K−1 dependingon the combination of metals, with a variation of in-plane to out-of-plane TE ratio ranging from 1.5 to 2.8

Anisotropic Thermal Expansion in High-Entropy Multicomponent Alb2-Type Diboride Solid Solutions

High-entropy (HE) ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding. Among others, HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures. Herein, we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions, with four to seven transition metals, with the intent of understanding the thermal lattice expansion following different composition or synthesis process. As a result, we were able to control the average thermal expansion (TE) from 1.3 x 10−6 to 6.9 x 10−6 K−1 dependingon the combination of metals, with a variation of in-plane to out-of-plane TE ratio ranging from 1.5 to 2.8

High coercitivity carbon embedded L10-FePt ferromagnetic nanoparticles

Stoichiometric FePt nanoparticles in the tetragonal L10 phase, (Ku = 6.6?107 erg/cm3) are one of the leading candidates for next generation high-density recording media, allowing theoretical grain stability down to 3nm [1]. As-synthesized FePt nanoparticles produced by the conventional soft chemical route (polyol process) [2,3] shows disordered face centered cubic (fcc) structure with low Ku and superparamagnetic behavior at RT. The ordered L10 tetragonal structure is usually obtained by post-annealing in a reducing environment [4,5] giving rise to particle aggregation produced by sintering that affects significantly both the final particle size and the polidispersity. A preliminary work we performed pointed out that a direct synthesis of ferromagnetic particles, based on the decomposition of Fe(acac)3 and Pt(acac)2 in reducing solvent and inert atmosphere, is made possible by the increase of the reaction temperature at 290-330?C obtained by the use of Triton X-100 as solvent and polyvinylpyrrolidone (PVP) as protective agent. The resulting nanoparticles are ferromagnetic at RT with coercitive field (Hc) ranging from 0.4 to 1.0 KOe depending on the synthesis temperature. However, as evidenced by TEM analyses, they are magnetically aggregate and, for synthesis temperatures above 300?C, embedded in an amorphous matrix produced by partial decomposition of the solvent. These observations suggested us a novel approach to the synthesis of non-aggregate ferromagnetic nanoparticles. The basic idea is to block the nanoparticles in a rigid matrix, during the synthesis, before they become ferromagnetic, to prevent magnetic aggregation. Using PEG-600 as solvent and quickly raising the temperature above 300?C cause the polyol to condense in flakes. The rapid heating, joined to the increased viscosity, limits the diffusion of the nutrient phase to the growing nuclei, resulting in monodisperse nanoparticles, with a typical size ranging around 5nm (determined by XRD and TEM), randomly dispersed in the condensed matrix. In agreement with the XRD analysis, pointing out a disordered fcc structure, the magnetic measurements show at RT a superparamagnetic behaviour of the as-grown particles, with a blocking temperature TB of 60K and large distribution of energy barriers. The phase transformation to the ferromagnetic ordered tetragonal L10 structure is achieved by thermal annealing in dynamic high vacuum; the annealing transforms the organic matrix into amorphous carbon that preserves the original nanoparticle size and prevents the aggregation up to 1000?C, where it transforms into pyrolitic graphite. XRD shows the appearing of the L10 diffraction peaks after a 1 hour treatment at 650? and an almost complete phase transition after 4hours at the same temperature, where a coercitive field (Hc) of 2,5kOe at RT and 13kOe at 5K is detected. Annealing at higher temperatures, even if results in a further enhancement of the structural properties, gives rise to complex behaviour of the hysteresis, whose origin is still under investigation

Optimal hydrogen storage in sodium substituted lithium fullerides

A relevant improvement in the hydrogen storage capability of lithium fullerides is obtained by the co-intercalation of a small amount of sodium

Influence of Vacancies in Manganese Hexacyanoferrate Cathode for Organic Na‐Ion Batteries: A Structural Perspective

Manganese hexacyanoferrates (MnHCF) are promising positive electrode materials for non-aqueous batteries, including Na-ion batteries, due to their large specific capacity (>130 mAh g$^{–1}$), high discharge potential and sustainability. Typically, the electrochemical reaction of MnHCF associates with phase and structural changes, due to the Jahn-Teller (JT) distortion of Mn sites upon the charge process. To understand the effect of the MnHCF structure on its electrochemical performance, two MnHCF materials with different vacancies content are investigated herein. The electrochemical results show that the sample with lower vacancy content (4 %) exhibits relatively higher capacity retention of 99.1 % and 92.6 % at 2$^{nd}$ and 10$^{th}$ cycles, respectively, with respect to 97.4 % and 79.3 % in sample with higher vacancy content (11 %). Ex-situ X-ray absorption spectroscopy (XAS) and ex situ X-ray diffraction (XRD) characterization results show that a weaker cooperative JT-distortion effect and relatively smaller crystal structure modification occurred for the material with lower vacancies, which explains the better electrochemical performance in cycled electrodes

Extending the hydrogen storage limit in fullerene

Li6C60 has been chosen as the most representative system to study the hydrogenation mechanism in alkali-cluster intercalated fullerides. We present here a muon spin relaxation (mu SR) experiment that hints the chance to achieve a higher storage capacity on fullerene with respect to the values suggested in literature. Moreover, a linear relationship between the muonium adduct radical hyperfine frequency and the level of C-60 hydrogenation was found and it can be exploited to probe the C-60 hydrogenation level, giving more credit to this technique in the field of hydrogen storage materials. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Supporting Information: Unexpected chain of redox events in co-based Prussian blue analogues

Comprehensive characterizing information about the series of materials; crystal, composition, and hyperfine parameters of the 57Fe Mössbauer spectra of samples K2−δMn1–xCox[Fe(CN)6]; SAED and TGA patterns, HAADF-STEM images, ATR–FTIR, 57Fe Mössbauer spectra, and electrochemical galvanostatic profiles of the mentioned series of samples; calculated fit of XAS experiments; and plots of KCMF50 and KCF operando SXRD in a 10–54° 2Θ range (λ = 1.0332 Å).Peer reviewe

Dynamics and Spectroscopy with Neutrons—Recent Developments and Emerging Opportunities

This work provides an up-to-date overview of recent developments in neutron spectroscopic techniques and associated computational tools to interrogate the structural properties and dynamical behavior of complex and disordered materials, with a focus on those of a soft and polymeric nature. These have and continue to pave the way for new scientific opportunities simply thought unthinkable not so long ago, and have particularly benefited from advances in high-resolution, broadband techniques spanning energy transfers from the meV to the eV. Topical areas include the identification and robust assignment of low-energy modes underpinning functionality in soft solids and supramolecular frameworks, or the quantification in the laboratory of hitherto unexplored nuclear quantum effects dictating thermodynamic properties. In addition to novel classes of materials, we also discuss recent discoveries around water and its phase diagram, which continue to surprise us. All throughout, emphasis is placed on linking these ongoing and exciting experimental and computational developments to specific scientific questions in the context of the discovery of new materials for sustainable technologies.This research was funded by the Gipuzkoako Foru Aldundia under Grant Number 2020-CIEN-000009-01