Three Dimensional Superconductivity in FeSe with Tczero Up to 10.9 K Induced by Internal Strain

Polycrystalline sample FeSe was synthesized by a self-flux solution method which shows a zero resistance temperature up to 10.9 K and a Tconset (90% \rhon, \rhon: normal state resistivity) up to 13.3 K. The decrease of superconducting transition temperature by heat treatment indicates that internal crystallographic strain which plays the same effect as external pressure is the origin of its high Tc. The fluctuation conductivity was studied which could be well described by 3D Aslamazov-Larkin (AL) power law. The estimated value of coherence length \xic=9.2 \AA is larger than the distance between conducting layers (~6.0 \AA), indicating the three-dimensional nature of superconductivity in this compound.Comment: 5 figure

Disordered structure for long-range charge density wave order in annealed crystals of magnetic kagome FeGe

Recently, charge density wave (CDW) has been observed well below the order of antiferromagnetism (AFM) in kagome FeGe in which magnetism and CDW are intertwined to form an emergent quantum ground state. The mechanism of CDW precipitating from an A-type AFM of Fe kagome sublattice is intensively debated. The structural distortion originating from the CDW has yet to be accurately determined in FeGe. Here we resolved the structure model of the CDW in annealed FeGe crystals through single crystal x-ray diffraction via a synchrotron radiation source. The annealed crystals exhibit strong CDW transition signals exemplified by sharp magnetic susceptibility drop and specific heat jump, as well as intense superlattice reflections from 2 $\times$ 2 $\times$ 2 CDW order. Occupational disorder of Ge atoms resulting from short-range CDW correlations above $T_\mathrm{CDW}$ has also been identified from the structure refinements. The dimerization of Ge atoms along c axis has been demonstrated to be the dominant distortion for CDW. The Fe kagome and Ge honeycomb sublattices only undergo subtle distortions. Occupational disorder of Ge atoms is also proved to exist in the CDW phase due to the random selection of partial Ge sites to be dimerized to realize the structural distortion. Our work paves the way to understanding the unconventional nature of CDW in FeGe not only by solving the structural distortion below $T_\mathrm{CDW}$ and identifying fluctuations above it but also by rationalizing the synthesis of high-quality crystals for in-depth investigations in the future.Comment: 18 pages, 4 figures. Comments are welcom

Transient behavior and reaction mechanism of CO catalytic ignition over a CuO–CeO2 mixed oxide

As a key heterogeneous process, the catalytic oxidation of CO is essential not only for practical applications such as automotive exhaust purification and fuel cells but also as a model reaction to study the reaction mechanism and structure-reactivity correlation of catalysts. In this study, the variation in activity-controlling factors during CO catalytic ignition over a CuO-CeO 2 catalyst was investigated. The activity for CO combustion follows the decreasing order of CuO-CeO 2 > CuO > CeO 2. Except for inactive CeO 2, increasing temperature induces CO ignition to achieve self-sustained combustion over CuO and CuO-CeO 2. However, CuO provides enough copper sites to adsorb CO, and abundant active lattice oxygen, thus obtaining a higher hot zone temperature (208.3 °C) than that of CuO-CeO 2 (197.3 °C). Catalytic ignition triggers a kinetic transition from the low-rate steady-state regime to a high-rate steady-state regime. During the induction process, Raman, X-ray photoelectron spectroscopy, CO temperature-programmed desorption and IR spectroscopy results indicated that CO is preferentially adsorbed on oxygen vacancies (Cu +-[Ov]-Ce 3+) to yield Cu +-[C≡O]-Ce 3+ complexes. Because of the self-poisoning of CO, the adsorbed CO and traces of adsorbed oxygen react at a relative rate, which is entirely governed by the kinetics on the CO-covered surface and the heat transport until the pre-ignition regime. The Cu +-[C≡O]-Ce 3+ complex is a major contributor to CO ignition. The step-response runs and kinetic models showed that after ignition, a kinetic phase transition occurs from a CO-covered surface to an active lattice oxygen-covered surface. During CO self-sustained combustion, the rapid gas diffusivity and mass transfer is beneficial for handling the low coverage of CO. The active lattice oxygen of CuO takes part in CO oxidation

Precise in-situ infrared spectra and kinetic analysis of gasification under the H2O or CO2 atmospheres

Studying the mechanisms of bagasse conversion into syngas is essential to sustain the growing use of biomass in energy economy production. In this work, the precise kinetics of bagasse gasification with various gasification agents was firstly investigated employing insitu infrared spectra with Coats-Redfern integration, combining qualitative infrared spectroscopy allowed for kinetic analysis, so as to explore how the intermediate species vary in each basic reaction. The results demonstrate that the CO2 agent reduces the activation energy of nitryl after amino oxidation, making the lignin involved in gasification more easily as well as causing higher gasification efficiency. On the one hand, steam serving as a gasification agent enhances the concentration of hydroxyl groups and produces H2-rich syngas. On the other hand, the strong oxidizing hydroxyl group reduces the energy barrier of carbonyl and carboxyl groups in cellulose, which facilitates the gasification process. Furthermore, this study compared the effects of gasification agent (H2O or CO2) on syngas composition, reactor temperature distribution, carbon conversion rate, gasification efficiency, as well as low calorific value, providing essential information for understanding the micro-reaction pathways and pathway regulation during bagasse gasification. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Self-sustained CO Combustion Induced by CuCe0.75Zr0.25Oy Catalysts with Different Pore-forming Methods

CO self-sustaining combustion, induced by a CuCe0.75Zr0.25Oy catalyst, has been confirmed experimentally as an effective strategy to reduce serious environmental pollution and energy waste, which is caused by direct combustion of conventional converter gas in the steelmaking industry. In this paper, the effects of CuCe0.75Zr0.25Oy catalysts prepared by a sol-gel method via three different pore-forming agents (oxalic acid, cellulose and thermal decomposition) were investigated for their catalytic activity of self-sustained CO combustion. Additionally, characterization methods were used to obtain the structural properties of each catalyst. The results obtained show that the CuCe0.75Zr0.25Oy catalyst, as a sol-gel pore-forming agent, prepared from cellulose exhibits the highest activity among the three catalysts. Under the condition of a reaction gas (3% CO+5% O-2/N-2), the T-10 (70 degrees C), T-50 (73 degrees C) and T-90 (78 degrees C) of the cellulose catalyst are obviously lower than those of the other catalysts, where T-10, T-50 and T-90 denote the reaction temperature corresponding to the CO conversion of 10%, 50% and 90%, respectively. The reason is that the cellulose pore-forming agent promotes the formation of a multistage porous structure, which strengthens the synergistic effect between the Cu and Ce catalysts and changes the redox property of the overall catalyst. On the one hand, the strong synergy between CuO and CeO2 adjusts the dispersion and chemical state of copper nanoparticles. On the other hand, the oxygen vacancies generated locate at the copper-cerium interface enhance the ability of oxygen storage and oxygen release of the catalyst

Simultaneous catalytic elimination of CO, toluene and NH₃ over multifunctional CuCeZr based catalysts

Catalytic oxidation technology is a promising strategy to eliminate carbon monoxide (CO), volatile organic compounds (VOC) and other emissions from industrial boilers and to address ammonia (NH3) escape. Herein, we demonstrate the potential of copper-cerium-zirconium mixed oxides or those supported on TiO(2 )or ZSM-5 substrates for the simultaneous catalytic removal of CO, toluene and NH3. Among them, CuCeZr/ZSM-5 exhibits the best co-processing ability for mixed gases. In situ infrared spectroscopy analyses suggest that there is a competitive adsorption among CO, toluene and NH3, and the inhibition is in descending order of toluene>CO> NH3. Based on the physical-chemical characterizations, the Cu-Ce interfacial structure plays an important role in CO ignition at low temperatures. More importantly, the abundant acidic sites on the ZSM-5 support can improve the stability of adsorbed NH3 at high temperatures, resulting in the best NH3 catalytic oxidation performance of CuCeZr/ZSM-5 with no secondary pollutants of NOx. This study provides a strategy for the catalyst design to eliminate multiple pollutants targeting the properties of pollutants

The transport properties in antimony doped iron selenide Fe(Se1-xSbx)(0.92) system

status: publishe

Spin dependence of the magnetization step in the Pr-doped manganites

Magnetic measurements were performed to study a single crystal Pr0.5Sr0.5MnO3 and polycrystalline Pr0.6Ca0.4MnO3. Magnetic-field$\hbox{--}$induced magnetization step is observed at low temperature for Pr-doped phase-separated manganites. Magnetization measurements indicate that the spin-stiffness constant D exhibits large magnetic-field dependence. Moreover, there exists a remarkable change of the spin-stiffness constant corresponding to the variety of the step-like magnetization. Our results suggest that the spin-wave inherent to the coexistence of the antiferromagnetic and ferromagnetic phases plays a crucial role in the mechanism of these magnetic transformations