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  • 1
    Electronic Resource
    Electronic Resource
    Growth twins in nanocrystalline SnO2 thin films by high-resolution transmission electron microscopy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7688-7694 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth twins in nanocrystalline SnO2 thin films with grain size 5–50 nm have been investigated by high-resolution transmission electron microscopy. They show the {101}〈101〉 geometry, metal atom mirror symmetry, and slight distortion of oxygen atoms. Multiple twins and step twin boundaries with a density about 1015 m−2 were frequently observed in the films. It appears there are tin interstitials at step twin boundaries and, hence, electronic donors associated with the interstitials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362434
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative Comparison of Transmission Electron Microscopy Techniques for the Study of Localized Ordering on a Nanoscale (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Different transmission electron microscopy techniques have been compared for the detection and size measurements of ordered regions on a nanometer scale in a disordered matrix phase. As a model system, the perovskite lead magnesium niobate doped with varying amounts of La has been chosen for the present study. While selected area electron diffraction can reveal the existence of ordered structures, dark-field contrast micrographs are usually used to reveal the spatial distribution and the size of ordered regions. However, for small ordered regions, a few nanometers in diameter, the measurements are no longer accurate because of superposition in projection. High-resolution transmission electron microscopy (HRTEM) combined with image processing is shown to be a suitable technique to provide a quantitative measurement of such localized ordering. The detection limit of this method is discussed in detail, using the experimental results and HRTEM image simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02379.x
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and Chemistry of Intergranular Glassy Films in Liquid-Phase-Sintered Alumina (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Analytical and high-resolution transmission electron microscopies were used to study the structure and chemistry of two-grain boundaries and three-grain junctions in polycrystalline alumina sintered with additions of between 0 and 10 wt% calcium silicate. Addition of calcium silicate greatly aided full densification and resulted in the presence of a continuous, amorphous grain-boundary film at the majority of the two-grain boundaries, the thickness of which was independent of the bulk level of additive. The chemistry of the glass at the grain boundaries and the three-grain junctions was notably different. The grain boundaries showed strong segregation of calcium, whereas both silicon and calcium appeared to favor triple pockets and larger-volume facets at the grain boundaries. Grain-triple-pocket interfaces also showed segregation of calcium. The overall extent of segregation appeared to be independent of the additive level. The amorphous grain-boundary film was of nominal composition CaO6Al2O3 and contained predominantly octahedrally coordinated aluminum within the glass. The triple pockets were generally of a composition within the primary-phase field of anorthite and contained tetrahedrally coordinated aluminum and silicon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02343.x
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  • 4
    Electronic Resource
    Electronic Resource
    Dopant Distribution in Grain-Boundary Films in Calcia-Doped Silicon Nitride Ceramics (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Quantitative analyses of the local chemistry of amorphous films at the grain boundary (GB) were taken on hot isostatically pressed high-purity Si3N4 doped with various amounts of calcium (up to 450 ppm). This work was mainly accomplished by using spatially resolved electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. The amount of calcium segregation, quantified in terms of GB excess, saturated in the films at a bulk-doping level of ∼220 ppm. Extra additives did not stay at the triple-point glass pockets, where the calcium was almost expelled completely; instead, the additives stayed at intersections between the films and pockets. Otherwise, the calcium distribution was uniform along and across GB films. The latter was determined from simulations of EELS profiling. At grain/pocket interfaces, a much-lower segregation level occurred, ranging from one-half to one-tenth of the level at the GB. This observation indicates different segregation mechanisms in the two cases. Also, the calcium segregation in GB films changed the film composition dramatically, because more N3− ions were introduced and replaced O2− ions, to maintain the local stoichiometry. Reduction of the Van der Waals force has been proposed as being the origin of the film expansion with increasing calcium content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02747.x
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  • 5
    Electronic Resource
    Electronic Resource
    Transient Growth Bands in Silicon Nitride Cooled in Rare-Earth-Based Glass (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Silicon nitride (Si3N4) particles embedded in various R-SiAl-O-N glasses (R = La, Nd, Gd, Yb) have been systematically studied by high-resolution transmission electron microscopy and by analytical electron microscopy. The particles typically show an internal growth band, which is attributed to the enhanced growth of the particles in the supersaturated silicate liquid during cooling and reheating. The electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy analysis reveal that the growth band typically contains lanthanide elements. This trapping, especially of the lighter lanthanide elements, within the lattice of the β-SiAlON is obviously beyond the general expectation that the lighter lanthanide ions hardly form solid solutions with either α- or β-Si3N4. This ultimately provides some clues regarding the mobility of the lanthanide ions in the liquids and also revives interest in the general question of the possible effect of a cooling stage on the structures and compositions of the intergranular film and of the grain/glass interface in the Si3N4-based polycrystalline ceramics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02997.x
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  • 6
    Electronic Resource
    Electronic Resource
    Silicon nitride crystal structure and observations of lattice defects (1996)
    Springer
    Journal of materials science 31 (1996), S. 5281-5298 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In view of the considerable progress that has been made over the last 40 years on the microstructural design of silicon nitride and related materials of tailored properties for specific applications, a clear review of the current understanding of the crystal structure and crystal chemistry of silicon nitride is timely. The crystal structures, crystal chemistry, and lattice defect nature of silicon nitride are critically reviewed and discussed, with emphasis placed firstly on the structural nature of α-silicon nitride (whether it is a pure silicon nitride, or should better be regarded as an oxynitride); and secondly on the space group of β-silicon nitride (whether it is P63/m or P63). In conjunction with recent observations of vacancy clusters in α-silicon nitride, a comprehensive view compatible with all the experimental facts with respect to the structural nature of α-silicon nitride is tentatively presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159294
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  • 7
    Electronic Resource
    Electronic Resource
    Crystallographic shear planes in nanocrystalline SnO2 thin films by high-resolution transmission electron microscopy (1996)
    Springer
    Journal of materials science 31 (1996), S. 2317-2324 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Atomic structures of crystallographic shear planes (CSPs) in nanocrystalline thin films of semiconductor SnO2 were investigated by high-resolution electron microscopy. The films were prepared by electron beam evaporation in high vacuum (10−6 torr) and followed by annealing in synthetic air at 700 °C for 1–2 H. CSPs with the displacement vector of [1/2 0 1/2] were observed in the planes parallel to (¯101), (110) and (¯3¯21). Most of the CPSs were found to terminate or interact with each other within SnO2 crystallites. Partial dislocations exist at terminal places of CSPs or along intersecting lines of CSPs. CSP steps were also observed. Structural models of these defects have been proposed. Based on analysis of experimental data, it has been suggested that the Sn/O ratio at CSPs which are not parallel to their displacement vector, at cores of partial dislocations and at CSP steps, is higher than that of the perfect structure, that is, these defects are able to provide extra free electrons with the films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01152940
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  • 8
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    The grain boundary mobility tensor (2020)
    National Academy of Sciences
    Details
    Publication Date: 2020-02-18
    Description: The grain-boundary (GB) mobility relates the GB velocity to the driving force. While the GB velocity is normally associated with motion of the GB normal to the GB plane, there is often a tangential motion of one grain with respect to the other across a GB; i.e., the GB velocity is a vector. GB motion can be driven by a jump in chemical potential across a GB or by shear applied parallel to the GB plane; the driving force has three components. Hence, the GB mobility must be a tensor (the off-diagonal components indicate shear coupling). Performing molecular dynamics (MD) simulations on a symmetric-tilt GB in copper, we demonstrate that all six components of the GB mobility tensor are nonzero (the mobility tensor is symmetric, as required by Onsager). We demonstrate that some of these mobility components increase with temperature, while, surprisingly, others decrease. We develop a disconnection dynamics-based statistical model that suggests that GB mobilities follow an Arrhenius relation with respect to temperature T below a critical temperatureTcand decrease as1/Tabove it.Tcis related to the operative disconnection mode(s) and its (their) energetics. For any GB, which disconnection modes dominate depends on the nature of the driving force and the mobility component of interest. Finally, we examine the impact of the generalization of the mobility for applications in classical capillarity-driven grain growth. We demonstrate that stress generation during GB migration (shear coupling) necessarily slows grain growth and reduces GB mobility in polycrystals.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Stable iridium dinuclear heterogeneous catalysts supported on metal-oxide substrate for solar water oxidation (2018)
    National Academy of Sciences
    Details
    Publication Date: 2018-03-05
    Description: Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single-atom catalysts (SACs) and nanoparticles (NPs). While SACs and NPs have been extensively reported, catalysts featuring a few atoms with well-defined structures are poorly studied. The difficulty in synthesizing such structures has been a critical challenge. Here we report a facile photochemical method that produces catalytic centers consisting of two Ir metal cations, bridged by O and stably bound to a support. Direct evidence unambiguously supporting the dinuclear nature of the catalysts anchored on α-Fe2O3 is obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM). Experimental and computational results further reveal that the threefold hollow binding sites on the OH-terminated surface of α-Fe2O3 anchor the catalysts to provide outstanding stability against detachment or aggregation. The resulting catalysts exhibit high activities toward H2O photooxidation.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Critical current density and resistivity of MgB2 films (2003)
    American Institute of Physics
    Details
    Publication Date: 2003-07-07
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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