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排序方式: 共有412条查询结果,搜索用时 31 毫秒
51.
Anuj Pokle Daniel Weber Matteo Bianchini Jürgen Janek Kerstin Volz 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(4):2205508
In lithium ion batteries (LIBs), the layered cathode materials of composition LiNi1−x−yCoxMnyO2 are critical for achieving high energy densities. A high nickel content (>80%) provides an attractive balance between high energy density, long lifetime, and low cost. Consequently, Ni-rich layered oxides cathode active materials (CAMs) are in high demand, and the importance of LiNiO2 (LNO) as limiting case, is hence paramount. However, achieving perfect stoichiometry is a challenge resulting in various structural issues, which successively impact physicochemical properties and result in the capacity fade of LIBs. To better understand defect formation in LNO, the role of the Ni(OH)2 precursor morphology in the synthesis of LNO requires in-depth investigation. By employing aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and precession electron diffraction, a direct observation of defects in the Ni(OH)2 precursor preparedis reported and the ex situ structural evolution from the precursor to the end product is monitored. During synthesis, the layered Ni(OH)2 structure transforms to partially lithiated (non-layered) NiO and finally to layered LNO. The results suggest that the defects observed in commercially relevant CAMs originate to a large extent from the precursors, hence care must be taken in tuning the co-precipitation parameters to synthesize defect-free Ni-rich layered oxides CAMs. 相似文献
52.
Xiaohong Tang K. Peter D. Lagerlöf Arthur H. Heuer 《Journal of the American Ceramic Society》2003,86(4):560-65
The breakup of dislocation dipoles in plastically deformed samples of undoped and 30-ppm-MgO-doped sapphire (α-Al2 O3 ) was monitored using conventional TEM techniques. Dislocation dipoles break up into prismatic dislocation loops in a sequential process during annealing; i.e., dislocation loops are pinched off at the end of a dislocation dipole. This pinch-off process is primarily controlled by pipe diffusion, and pipe diffusion coefficients at temperatures between 1300° and 1500°C were estimated by monitoring the kinetics of the dipole breakup process. We determined D P U = 8.1(–4.3 +9.1 ) × 10–3 exp [–(4.5 ± 1.3 eV )/ kT )] m2 /s for the undoped material. The pipe diffusion kinetics for the MgO-doped crystal was determined at 1250° and 1300°C and was about 6 times higher than for undoped sapphire. Finally, climb dissociation of the dislocations constituting the perfect dipoles in sapphire is common; annihilation of one set of partials can result in the formation of faulted dipoles, which can pinch off to form faulted dislocation loops. D P U for faulted dipoles in the undoped material was determined at 1300° and 1350°C, and was about 4–10 times higher than for perfect dipoles. 相似文献
53.
Composite Ag(Br,I) tabular microcrystals of photographic emulsions were studied by the combination of energy-filtering electron microscopy (EFTEM) and electron energy-loss spectroscopy (EELS) in conjunction with energy-dispersive X-ray (EDX) microanalysis. The contrast tuning under the energy-filtering in the low-loss region was used to observe more clearly edge and random dislocations, {11− 1} stacking faults in the grain shells parallel to {11− 2} edges and bend and edge contours. Electron spectroscopic diffraction patterns revealed numerous extra reflections at commensurate positions in between the Bragg reflections and diffuse honeycomb contours; these were assigned to the number of defects in the shell region parallel to the grain edges and polyhedral clusters of interstitial silver cations, respectively. Inner-shell excitation bands of silver halide were detected and confirmed by EDX analyses, i.e. the Ag N2,3 edge at 62 eV (probably overlapped with the weak I N4,5 edge at 52 eV and the Br M4,5 edge at 70 eV), the I M4,5 edge at about 620 eV, and the Br L2,3 edge at about 1550 eV energy losses. Energy-loss near-edge structure of the Ag M4,5 edge at about 367 eV energy losses and low-loss fine structure arisen as a result of interband transitions and excitons, possibly superimposed with many electron effects, have been revealed. The crystal thickness was determined by a modified EELS log-ratio technique in satisfactory agreement with measurements on grain replicas. 相似文献
54.
Modeling of complex interfaces: Gadolinium‐doped ceria in contact with yttria‐stabilized zirconia
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Xavier Aparicio‐Anglès Nora H. de Leeuw 《Journal of the American Ceramic Society》2017,100(7):3329-3339
Gadolinium‐doped ceria (GDC) and yttria‐stabilized zirconia (YSZ) are well‐known electrolyte materials in solid oxide fuel cells (SOFCs). Although they can be used independently, it is common to find them in combination in SOFCs, where they are used as protective layers against the formation of secondary phases or electron conduction blockers. Despite their different optimum operating temperatures, it appears that oxygen conduction is not affected by their interface. However, the intrinsic mechanisms of oxygen diffusion at these interfaces still remain unclear. One of the main difficulties when modeling the contact between different materials, or indeed different particles of the same material, is caused by the structural complexity of these systems. If we wish to evaluate the properties of the materials, we first need to obtain a model that includes the main features of the GDC/YSZ interface, such as large‐scale defects or cation interdiffusion in the contiguous phase. Since the generation of such a mixed system is complicated, we show here how the “amorphization and recrystallization” strategy can help us to obtain realistic systems. In this, the first of our papers on the structure and properties of layered GDC/YSZ materials, we discuss the structural features of the grain boundary between GDC and YSZ obtained by molecular dynamics simulations. 相似文献
55.
56.
M. H. Yoo 《Intermetallics》1998,6(7-8):597-602
Based on the recent studies of deformation twinning in ordered intermetallics, the general background on slip-twinning-microcracking relationships is established. Specific roles of deformation twinning in the generalized plasticity of polycrystals and the crack-tip microplasticity are discussed in terms of the local strain compatibility by invoking both ‘tension’ and ‘compression’ twins. Special examples are given for γ-TiAl, other L10 alloys, and Ti3Al of the D019 structure. Effects of composition, microstructure and temperature on defect properties that are relevant to the propensity of deformation twinning are discussed. 相似文献
57.
应用TEM研究了L12长程有序结构Ni74.5Pd2Al23.5合金的室温变形组织。研究结果表明:添加Pd元素韧化的Ni74.5Pd2Al23.5合金的变形组织中存在着大量超点阵内禀层错。绝大部分层错的边界位错是沿〈011〉分布的肖克莱偏位错环,其中30°的a/3〈112〉超肖克莱位错处于固定状态。这类位错的可动性较差,但其固定程度较合金中普遍存在的KearWilsdorf固定位错要弱。 相似文献
58.
J. Shen R. Balasubramanian D. K. Aidun L. L. Regel W. R. Wilcox 《Journal of Materials Engineering and Performance》1998,7(4):555-563
CdTe crystals were uniaxially compressed along several crystallographic axes at temperatures from 773 to 1353 K. The applied
stress ranged from 14 to 74% of the critical resolved shear stress (CRSS) measured in the authors’ laboratory. The deformed
specimens were annealed without applying stress at temperatures from 573 to 1073 K. No twins were observed after the above
operations. Dense slip bands were observed on most of the compressed specimens. Secondary slip systems were activated in some
experiments. CdTe crystals were sheared along {111}<112> at 1073 K with a load of 40% CRSS. Slip bands, but no twins, were
observed. Synchrotron x-ray topography was used to study in situ the effect of stress on crystal deformation. CdTe specimens
were uniaxially stressed in tension along <112> at 293 to 673 K. When the load reached ~50% of the CRSS, the topograph began
to distort, indicating the beginning of plastic deformation. No twins were observed on the stressed specimens. 相似文献
59.
Shigeo Horiuchi Marco Cantoni Masaya Uchida Tadamasa Tsuruta Yoshio Matsui 《Bulletin of Materials Science》1999,22(3):227-231
Quantized magnetic flux lines (vortices) in a Nb foil were directly observed in different magnetic fields up to 200 G by a
cryo-Lorentz electron microscope. The interaction of vortices with dislocations in the specimen was examined and clarified;
edge-on dislocations weakly pin individual vortices at magnetic fields below 100 G. In higher magnetic fields the formation
of a regular hexagonal vortex lattice started preferentially at in-plane dislocations. At 200 G the Abrikosov vortex lattice
was formed with small domains, whose centre included the dislocations, showing their important role on the formation of the
vortex lattice. For a NbTi foil no clear image of vortices could be seen, because the surface was rough due to the formation
of fine grains and precipitates. 相似文献
60.
Using an interface between Cu/Ti as an example, two HREM-based image analysis techniques, strain mapping and iterative digital image matching, are compared. The validity limit of these techniques is discussed as a function of specimen thickness and microscope technology. Two criteria are used to assess the limits: (i) the difference between two geometric phase maps, one calculated in image plane and one in object plane, and (ii) a difference image from two HREM simulations of two structure models differing in one atomic column. The latter displays the overall delocalisation of information by the microscope due to diffraction and imaging. It is outlined how far images and strain maps, obtained for high-voltage microscopy at 1250 kV and C S correction at 200 kV, are identical. Both techniques exhibit a significantly increased regime of applicability of strain mapping near defect cores. Simulations for a 400 kV HREM and a 300 kV FEGTEM with and without focal series reconstruction complement the study. 相似文献