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91.
Zihan Wang Qiao Yuan Yunfei Zhang Min Ma Daojiang Gao Jian Bi Jiangtao Wu 《Ceramics International》2021,47(13):17877-17882
Despite being difficult to identify, extremely dilute oxygen vacancies have been widely reported to play an important role in enhancing magnetism in ZnFe2O4. The mechanisms underlying this enhanced magnetism have not been well understood for a long time and remain controversial because the formation of oxygen vacancy-rich ZnFe2O4 can be accompanied by changes in the chemical/physical characteristics, especially the composition, particle size, surface morphology and cation distribution, which can significantly affect the magnetization. An open and important question is whether and to what extent the enhanced magnetization can be attributed only to oxygen vacancies. In this study, the relationship between the magnetization and oxygen vacancies in ZnFe2O4 was definitively determined by using a carefully designed “shake-and-heat” treatment to prepare vacancy-rich samples while keeping the other crystal/surface parameters constant. Compared to the nearly vacancy-free paramagnetism samples, the vacancy-rich samples exhibited a higher magnetization of approximately 5 emu/g at both 300 K and 2 K. The Fe3+-O2--Fe3+ superexchange paths broken by oxygen vacancies then resulting in the Fe3+-Fe3+ ferromagnetism configuration. Meanwhile, the oxygen vacancy is highly diluted then the ferromagnetism configuration is confined in a single super-cell, favoring a short-range magnetic ordering at room temperature. The concentration of oxygen vacancies was calculated to be 0.68% by magnetization measurement. Our results may shed a light on how oxygen vacancies affect magnetism. 相似文献
92.
Yangsen Xu Xi Xu Ning Cao Xianfen Wang Xuehua Liu Marco Fronzi Lei Bi 《International Journal of Hydrogen Energy》2021,46(17):10293-10302
The electrochemical conversion of N2 to NH3 is an interesting research topic as it provided an alternative and energy-saving method compared with the traditional way of NH3 production. Although different materials have been proposed for N2 reduction, the use of defects in oxides was only reported recently and the relevant working mechanism was not fully revealed. In this study, Sr was used as the dopant for LaFeO3 to create oxygen vacancies, forming the Sr-doped LFO (La0.5Sr0.5FeO3-δ) perovskite oxide. The La0.5Sr0.5FeO3-δ ceramic oxide used as a catalyst achieves an NH3 yield of 11.51 μgh?1 mg?1 and the desirable faradic efficiency (F.E.) of 0.54% at ?0.6 V vs reversible hydrogen electrode (RHE), which surpassed that of LaFeO3 nanoparticles. The 15N isotope labeling method was employed to prove the La0.5Sr0.5FeO3-δ catalyst had the function of converting N2 into NH3 under the electrolysis condition. The first principle calculations were used to investigate the mechanism at the atomistic level, revealing that the free energy barriers changed significantly with the introduction of oxygen vacancies that accelerated the overall nitrogen reduction reaction (NRR) procedure. 相似文献
93.
94.
Yanhong Quan Ning Zhang Zhilei Zhang Yahong Han Jinxian Zhao Jun Ren 《International Journal of Hydrogen Energy》2021,46(27):14395-14406
A series of Ni/ZrO2 catalysts was prepared by the impregnation method with modification of the morphology of ZrO2 support as well as the impregnation procedure and tested for CO2 methanation. The catalysts supported on the ZrO2 nanosheets displayed superior catalytic performance as compared with that on ZrO2 nanoparticles, which could be mainly attributed to the abundant oxygen vacancies promoting the adsorption and dissociation of CO2 molecules as well as the high dispersion of Ni species. With the introduction of ethylenediamine (En) in the impregnation procedure, the resulting Ni-15En/ZrO2-1.5 catalyst showed the optimal activity with CO2 conversion of 86% significantly higher than Ni/ZrO2-0 of 44% and Ni/ZrO2-1.5 of 79% at 0.5 MPa and 300 °C. The excellent performance was attributed to increased moderately basic sites for CO2 adsorption in ZrO2 nanosheets, as well as the enhanced dispersion of nickel caused by the complexation of Ni ions with En, which inhibited the aggregation of nickel particles in the subsequent thermal treatments. In conclusion, the synergistic effects of the morphology of ZrO2 nanosheets as well as the chelating behavior of En contributed to the enhanced performance of Ni-15En/ZrO2-1.5 in the CO2 methanation reaction. The strategy shows good prospects for controlling the size of active metals, especially those that were dispersed on the surface of the two-dimensional (2D) metal oxide materials. 相似文献
95.
《Journal of the European Ceramic Society》2023,43(5):2023-2032
Ta-doped solid-state electrolyte (SSE) is employed to reveal Li vacancy regulation process and densification mechanism through thermodynamic analysis. The vacancy concentration has an optimal value corresponding to the lowest free energy of the Ta-doped SSE system. Low system free energy accelerates grain growth and promotes grain fusion for SSE densification, which is consistent with microstructure evolution. The relative density and Li-ion conductivity reach 96.1 % and 6.47 × 10?4 S cm?1 at 0.5 of Ta doping. Symmetric Li battery exhibits stable cycling at a high current density of 1.41 mA cm?2 and cycles 250 h without polarization at 0.2 mA cm?2. Full battery with LiFePO4 cathode keeps stability with high Coulombic efficiency of ~99 % after 150 cycles at 0.5 C. This work provides theoretical insights into the Li vacancy regulation of Ta-doped SSE, constituting a significant step toward practical applications. 相似文献
96.
《Journal of the European Ceramic Society》2023,43(4):1625-1632
During thermal annealing at 1425 °C nominal electric field strengths of 50 V/mm and 150 V/mm were applied along the grain boundary planes of a near 45° (100) twist grain boundary in SrTiO3. Electron microscopy characterization revealed interface expansions near the positive electrode around 0.8 nm for either field strength. While the interface width decreased to roughly 0.4 nm after annealing at 50 V/mm, the higher field strength caused decomposition of the boundary structure close to the negative electrode. Electron energy-loss and X-ray photoelectron spectroscopies demonstrated an increased degree of oxygen sublattice distortion at the negative electrode side, and enhanced concentrations of Ti3+ and Ti2+ compared to bulk for both single crystals and bicrystals annealed with an external electric field, respectively. Oxygen migration due to the applied electric field causes the observed alteration of grain boundary structures. At sufficiently high field strength the agglomeration of anion vacancies may lead to the decomposition of the grain boundary. 相似文献
97.
Yanjie Wang Ruixue Gao Hongchao Zhao Jing Li Ruijie Zhang Yuhang Wang Yong Zhou 《Journal of the American Ceramic Society》2023,106(2):1050-1061
Ethanol vapor plays a significant role in the aspects of human health and industrial production, thus necessitating a swift, sensitive, and low-power ethanol detection in the field of future gas sensors. In this work, we prepared micro–electro–mechanical system ethanol sensors based on ZnO nanorods (NRs) and nanoparticles (NPs) for trace ethanol detection. Both ZnO samples were synthesized by a facile hydrothermal method. The comparison results exhibited that ZnO NRs based sensors prevailed over NPs-based counterparts in terms of sensitivity, optimal operation temperature, and reaction speeds. Briefly, that ZnO NRs-based sensors presented a large response (11.5 toward 5 ppm), fast response/recovery times (5 s/5 s), ultralow detection limit (400 ppb), and tiny power consumption (30 mW) at 245°C, surpassing most of recently reported ethanol sensors and commercial products based metal oxides. The abundant oxygen vacancies, large specific surface area, and porous structure were primarily responsible for the excellent sensor performance. This work also offers a facile and competitive approach to realize a sensitive and swift trace ethanol recognition with minimal power consumption, catering for the demanding requirements of future gas sensors in the fields of wearable devices and Internet of Things. 相似文献
98.
《Ceramics International》2023,49(19):30924-30936
Rare earth ion substitution is one of the most important methods for adjusting the magnetic properties of M-type hexagonal ferrites; however, the regularity of these phase formations has rarely been studied. In this work, La substituted Sr hexaferrite LaxSr1-xO·nFe2O3 (La-SrM, 4.9 ≤ n ≤ 6.0, 0 ≤ x ≤ 0.6) was prepared using the traditional ceramic method. The effects of the Fe/Sr molar ratio (n), calcining temperature, and La3+ substitution (x) on SrM phase formation, the crystalline structure, and magnetic properties were investigated. With an increase of x up to a maximum value of 0.5–0.6, a higher calcining temperature is required to form the single M-phase of La-SrM samples. However, the optimal n values of single-phase La-SrM samples differ as the La substitution varies: when x = 0.1, n = 5.5–6.0; x = 0.2, n = 5.5–5.9; x = 0.3, 0.4 and 0.5, n = 5.7–5.8. The magnetic measurements show that La0.2Sr0.8O·5.8Fe2O3 has the highest specific saturation magnetization (σs), which is 2.2% higher than that of unsubstituted SrM (SrO·6Fe2O3), while the anisotropic field (HA), the anisotropic constant (K1), and Neel point (TN) of La3+ substituted SrM decreased. Detailed structure analyses were conducted to explain the changes in magnetic properties. Fe3+ in the spin-up 2a sublattice of LaxSr1-xO·5.8Fe2O3 decreased by approximately 5% from 98.5% (x = 0) to 93.85% (x = 0.4) with an increase in x. Additionally, a small amount of Fe3+ was reduced to Fe2+ in the spin-down 4f2 sublattice with the maximum reduction amount of 4.13% reached at x = 0.2, thereby improving σs. The decrease in the bond angle of (4f1) Fe3–O2–Fe5 (12k), (2a) Fe1–O4–Fe3 (4f1), and (4f1) Fe3–O4–Fe5 (12k) lead to the weakening of Fe–O–Fe superexchange of La-SrM so that HA, K1, and Tn decreased with increasing values of x. This work lays a solid foundation for the study of process regulation and ion substitution of permanent magnet ferrite. 相似文献
99.
《Ceramics International》2023,49(20):32739-32749
In recent years, the exploration of hazardous gases at room temperature (RT) has remained one of the key focuses in the research field of the semiconductor gas sensors. Herein, mesoporous manganese-cobalt (Mn–Co) oxides with abundant oxygen vacancies were synthesized by the combustion method assisted with the green reducing agent l-Ascorbic acid (LA). The synthesized Mn–Co oxides were performed by X-ray spectroscopy (XPS) and Raman spectrometer to research their chemical state of surface elements. The results manifested that the Mn–Co oxides with LA adding during preparation possessed abundant oxygen vacancies. Additionally, the gas sensitivity tests indicated that the Mn–Co oxides with a mole ratio of LA to metal elements (MCO-0.3L) exhibited best formaldehyde sensing properties compared to other prepared Mn–Co oxides in the concentration of 0.25–30 ppm at RT. Notably, its response to 5 ppm formaldehyde at RT was more than 7 times of that of the Mn–Co oxides prepared without LA adding (8.1 vs 1.1). The MCO-0.3L sensor has a limit of detection (LOD) as low as 5.2 ppb. It also showed good selectivity and reliability. The improved formaldehyde sensitivity of the Mn–Co oxides sensors is supposed as the synergistic action of the abundant oxygen vacancies and the mesoporous structure. 相似文献
100.
Jiahui Li Chuanfeng Zhang Yang Liu Biyun Fang Jun Ni Jianxin Lin Bingyu Lin Lilong Jiang 《American Institute of Chemical Engineers》2023,69(11):e18194
Synergistic optimization of nitrogen dissociation and hydrogen transfer might be an efficient strategy to develop a highly efficient ammonia synthesis catalyst. Herein, the Ni-modified molybdenum nitride is used as the catalyst of ammonia synthesis. The presence of the highly dispersed Ni metal results in enhancement of nitrogen vacancy, causing the acceleration of the exchange and reaction of the lattice N species with the nitrogen species from the gaseous phase. In addition, the presence of Ni species facilitates the hydrogen transfer and spillover, as well as easy hydrogen release. As a result, the optimized molybdenum nitride catalyst with 0.1 wt% Ni shows a 2.5-times higher catalytic activity than that of the catalyst without Ni species at 400°C owing to the coupling of nitrogen activation and hydrogen transfer effects. This general approach could inspire the rational design of other metal catalysts for ammonia synthesis. 相似文献