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排序方式: 共有3279条查询结果,搜索用时 15 毫秒
1.
Liangtao Yang Liang-Yin Kuo Juan Miguel López del Amo Prasant Kumar Nayak Katherine A. Mazzio Sebastian Maletti Daria Mikhailova Lars Giebeler Payam Kaghazchi Teófilo Rojo Philipp Adelhelm 《Advanced functional materials》2021,31(38):2102939
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. 相似文献
2.
Cadmium selenide films were synthesized using simple electrodeposition method on indium tin oxide coated glass substrates. The synthesized films were post annealed at 200 °C, 300 °C and 400 °C. X-ray diffraction of the films showed the hexagonal structure with crystallite size <3 nm for as deposited films and 3–25 nm for annealed films. The surface morphology of films using field emission scanning electron microscopy showed granular surface. The high resolution transmission electron microscopy of a crystallite of the film revealed lattice fringes which measured lattice spacing of 3.13 Å corresponding to (002) plane, indicating the lattice contraction effect, due to small size of CdSe nanocrystallite. The calculation of optical band gap using UV–visible absorption spectrum showed strong red-shift with increase in crystallite size, indicating to the charge confinement in CdSe nanocrystallite. 相似文献
3.
Zehu Xie Na Peng Tingting Liu Xing Cheng Wuquan Ye Runtian Zheng Jundong Zhang Haoxiang Yu Jie Shu 《Ceramics International》2019,45(9):11812-11818
Here, LiY(WO4)2 nanotubes are prepared via a feasible electrospinning technique. This new anode material shows excellent electrochemical properties. The capacity loss of LiY(WO4)2 nanotubes is as low as 6.9% after 156 cycles, while bulk LiY(WO4)2 presents the capacity loss higher than 55.0%. Even after 600 long-life cycles, the capacity loss of the nanotubes is only 9%. It can be seen that the hollow structure with a rough surface and a porous morphology contributes to the improvement of electrochemical performance. Furthermore, online X-ray diffraction (XRD) method is firstly applied to understand the lithium ions insertion/extraction mechanism of LiY(WO4)2 nanotubes. It can be concluded that it is an asymmetrical two-phase reaction. A phase transformation from LiY(WO4)2 to Li3Y(WO4)2 can be obviously seen from the in situ XRD during discharge process. While Li2Y(WO4)2 appears as an intermediate phase with a reverse charge reaction. In addition, in situ XRD also demonstrates that LiY(WO4)2 nanotubes have surprised electrochemical reversibility. All the above results indicate that LiY(WO4)2 nanotubes can be expected to be anode candidate for rechargeable lithium ion batteries (LIBs). 相似文献
4.
《Ceramics International》2015,41(8):9373-9382
The aim of this work was to study the bioactivity of systems based on a clinically tested bioactive glass (BG) particulates (mol%: 4.33 Na2O−30.30 CaO−12.99 MgO−45.45 SiO2−2.60 P2O5−4.33 CaF2) and organic carriers. The cohesiveness of injectable bone graft products is of high relevance when filling complex volumetric bone defects. With this motivation behind, BG particulates with mean sizes within 11−14 μm were mixed in different proportions with glycerol (G) and polyethylene glycol (PEG) as organic carriers and the mixtures were fully injectable exhibiting Newtonian flow behaviors. The apatite forming ability was investigated using X-ray diffraction and field emission scanning electron microscopy under secondary electron mode after immersion of samples in simulated body fluid (SBF) for time durations varying between 12 h and 7 days. The results obtained revealed that in spite of the good adhesion of glycerol and PEG carriers to glass particles during preparation stage, they did not hinder the exposure of bioactive glass particulates to the direct contact with SBF solution. The results confirmed the excellent bioactivity in vitro for all compositions expressed by high biomineralization rates with the formation of crystalline hydroxyapatite being identified by XRD after 12 h of immersion in SBF solution. 相似文献
5.
The aim of this article is to synthesis tungsten oxide (WO3) nanoparticle along with Manganese (3 wt% and 10 wt%) by Microwave irradiation method. The physical properties of the synthesized Manganese doped Tungsten oxide materials were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM), UV-Diffuse Reflectance Spectroscopy, SEM-EDAX and Photoluminescence studies. The predominant peaks obtained in X-ray diffraction pattern reveal the crystalline nature of the nanoparticles and the structure belongs to Monoclinic for pure and Mn doped WO3. FTIR analysis shows the presence of Tungsten and oxygen in the synthesis material and verified with EDAX. TEM analysis shows both pristine and Mn doped WO3 nanopaticles. They are having spherical shaped morphology with average particle size from 35 to 40 nm. UV-DRS revealed that the bandgap energy for pure and Manganese doped WO3 are discussed in this article. The Scanning Electron Microscope analysis shows the plate like morphology for pure WO3 and the morphology were decreased by doping Manganese. The defects and oxygen deficiencies were analysed by photoluminescence spectroscopy. 相似文献
6.
Manika Chaudhary Milan Singh Ashwani Kumar Yogendra K. Gautam Anil K. Malik Yogesh Kumar Beer Pal Singh 《Ceramics International》2021,47(2):2094-2106
The current research work presents a facile and cost–effective co-precipitation method to prepare doped (Co & Fe) CuO and undoped CuO nanostructures without usage of any type of surfactant or capping agents. The structural analysis reveals monoclinic crystal structure of synthesized pure CuO and doped-CuO nanostructures. The effect of different morphologies on the performance of supercapacitors has been found in CV (cyclic voltammetry) and GCD (galvanic charge discharge) investigations. The specific capacitances have been obtained 156 (±5) Fg?1, 168(±5) Fg?1 and 186 (±5) Fg?1 for CuO, Co-doped CuO and Fe-doped CuO electrodes, respectively at scan rate of 5 mVs?1, while it is found to be 114 (±5) Fg?1, 136 (±5) Fg?1 and 170 (±5) Fg?1 for CuO, Co–CuO and Fe–CuO, respectively at 0.5 Ag-1 as calculated from the GCD. The super capacitive performance of the Fe–CuO nanorods is mainly attributed to the synergism that evolves between CuO and Fe metal ion. The Fe-doped CuO with its nanorods like morphology provides superior specific capacitance value and excellent cyclic stability among all studied nanostructured electrodes. Consequently, it motivates to the use of Fe-doped CuO nanostructures as electrode material in the next generation energy storage devices. 相似文献
7.
Martin Michálek Monika Michálková Gurdial Blugan Jakob Kuebler 《Ceramics International》2018,44(3):3255-3260
Up to now, commercially available alumina ceramics were claimed to have strength between 400 and 550 MPa. However, our study shows strength ~ 2 times higher for commercially available alumina than commonly believed. The average and characteristic strength, measured on 31 pure alumina ceramic discs by ball on three balls (B3B) test, were 1205 ± 93 MPa and 1257 MPa, respectively, with a Weibull modulus of m = 11.8. Tested specimens were in form of discs with a diameter of 5 mm and thickness 0.5 mm. The grain size distribution of the alumina is bimodal with an average grain size of ~ 850 nm measured at the surface. The fracture reveals a mixed transgranular / intergranular failure mode. To avoid incorporation of additional flaws, the discs were tested as sintered. The characteristic flexural strength measured in B3B was recalculated according to Weibull theory for standard 4-point bending bars of size 3 × 4 × 45 mm as bend 856 MPa. The measured strength of nearly 900 MPa shows the potential of strength for high purity alumina ceramics. 相似文献
8.
Maria Yousaf Lodhi Muhammad Azhar Khan Majid Niaz Akhtar Muhammad Farooq Warsi Asif Mahmood Shahid M. Ramay 《Ceramics International》2018,44(3):2968-2975
The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu2?xNixNdyFe28?yO46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd3+) as compared to (Fe3+), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å3). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd3+ ions at octahedral site impedes the valence alternation of Fe3+; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc). 相似文献
9.
The role of Nb2O5 and γ-Al2O3 oxide supports on the ammoxidation of propane on supported mixed Sb–V oxide at different Sb+V surface coverages is studied. Sb and V oxide species on alumina and on niobia support show different structural features that reflect in different performance during the ammoxidation of propane to acrylonitrile. Niobia-supported catalysts are much more selective to acrylonitrile than alumina-supported ones. Alumina interacts weakly with the supported oxides while niobia forms new phases through solid state reactions with the supported oxides during catalytic operation that must account for its higher selectivity values towards acrylonitrile and higher specific rate of acrylonitrile formation per vanadium site. 相似文献
10.
A previously proposed model of strain in ceria–zirconia-encapsulated precious-metal particles is revised to reflect several new observations: encapsulation of unstrained Pt particles, quantitative relation between partial reduction and the change in ceria–zirconia cell parameters, temperature/time dependence of strain relaxation/imposition in encapsulated Pd and Rh particles, and strained PdO. According to the revised model, the main cause of strain is partial oxidation of the precious metal (rather than the change in oxygen content of ceria–zirconia, as originally suggested). 相似文献