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  • 1
    Electronic Resource
    Electronic Resource
    Grain boundary electrical barriers in positive temperature coefficient thermistors (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2909-2913 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resistance–temperature, current–voltage, and capacitance–voltage characteristics have been measured in niobium-doped barium titanate bicrystals. The analysis by device simulation reveals that potential barrier with a semiconductor–insulator–semiconductor structure can consistently interpret the observed characteristics rather than the double Schottky barrier. Absence of sub-ohmic behavior in the current–voltage characteristics and excess low-frequency capacitance at zero bias are caused by the spatially distributed traps at the insulating layer. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371140
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  • 2
    Electronic Resource
    Electronic Resource
    Direct Characterization of Grain-Boundary Electrical Activity in Doped (Ba0.6Sr0.4)TiO3 by Combined Imaging of Electron-Beam-Induced Current and Electron-Backscattered Diffraction (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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: Simultaneous measurements of remote electron beam induced current (REBIC) and orientation imaging microscopy (OIM) in a scanning electron microscope (SEM) have been applied to a polycrystalline (Ba0.6Sr0.4)TiO3 with a positive temperature coefficient of resistivity (PTCR) to elucidate a grain-boundary character dependence of the potential barrier formation. The absence of electrical activity in a coherent Σ3 twin boundary is clearly imaged. The resistivity of individual grain boundaries estimated from a resistive contrast image is interpreted in terms of geometrical coherency, which is defined by the degree of coincidence in the reciprocal lattice points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01153.x
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  • 3
    Electronic Resource
    Electronic Resource
    Current–Voltage Characteristics of Cobalt-Doped Inversion Boundaries in Zinc Oxide Bicrystals (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), 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: Undoped and cobalt-doped basal inversion boundaries were fabricated in ZnO bicrystals to investigate their current–voltage characteristics. High-resolution transmission electron microscopy observations and energy-dispersive X-ray spectroscopy analyses for a cobalt-doped bicrystal revealed that the boundary was highly coherent and free from intergranular phases and precipitates, but a certain amount of cobalt was present near the boundary. The cobalt-doped bicrystals exhibited nonlinear characteristics that depended on cooling rates from annealing temperature, in contrast to linear characteristics of the undoped bicrystals. It is suggested that the presence of cobalt impurities enhances the formation of acceptor-like native defects near the boundaries to generate electrostatic potential barriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03526.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Cation Doping on the Superplastic Flow in Yttria-Stabilized Tetragonal Zirconia Polycrystals (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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: The superplastic characteristics of various cation-doped yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) were examined. For 1 mol% cation doping the true stress of Y-TZP is very dependent on the ionic radii of the doped cations; for instance, smaller cation radii give rise to lower true stress when compared with the other compositions for the same grain size, strain rate, and testing temperature. The altered true stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrO2. The strain to failure of the doped zirconia is affected by both ionic radius and valence of the dopant cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00920.x
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  • 5
    Electronic Resource
    Electronic Resource
    High-Temperature Tensile Deformation of Glass-Doped 3Y-TZP (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), 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: Amorphous grain boundary phases in 3-mol%-yttria-stabilized zirconia ceramics (3Y-TZP) were studied to determine the influence of intergranular amorphous silicate phases on tensile superplasticity at temperatures of 1300–1500°C. Controlled additions (1 wt%) of compositionally distinct barium silicate and borosilicate phases were used. The initial grain sizes of the pure, barium silicate added, and borosilicate-added samples were 0.45, 0.55, and 0.55 μm, respectively. Systems with added barium silicate and borosilicate glass both exhibited a 60% reduction in flow stress as compared with pure 3Y-TZP, with the lower-viscosity barium silicate system exhibiting a slightly greater reduction in flow stress. The higher-viscosity borosilicate glass/3Y-TZP materials exhibited the greatest elongation to failure, while the barium silicate/3Y-TZP materials had the least elongation. Yttrium was found to segregate to grain boundaries in the pure and borosilicate-containing samples, and both yttrium and barium were found to segregate to grain boundaries in the barium silicate containing samples. No silicon was observed along two-grain boundaries in any of the samples, even those containing pockets of glass. The difference in deformation behavior may be due to a combination of viscosity of the glass addition, grain boundary segregation, and grain boundary bond character.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01688.x
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  • 6
    Electronic Resource
    Electronic Resource
    Grain Growth of Silica-Added Zirconia Annealed in the Cubic/Tetragonal Two-Phase Region (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: The grain growth in silica-doped 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (SiO2-doped 3Y-TZP) and undoped 3Y-TZP has been examined in the temperature range of 1400°-1800°C. The presence of a SiO2 phase inhibits rather than promotes the grain growth in 3Y-TZP, particularly at high temperatures. During the grain growth in 3Y-TZP, yttrium ions are partitioned between grains, and the grain growth mechanism can be understood from Ostwald ripening dominated by lattice diffusion of cations. In SiO2-doped 3Y-TZP, an amorphous SiO2-rich phase exists only in the grain-boundary corners or junctions, not in the grain-boundary faces. The grain growth in SiO2-doped 3Y-TZP is controlled by using different mechanisms below and above the eutectic temperature of the zirconia-silica (ZrO2-SiO2) system. The glass phase does not have a major role in grain growth below the eutectic temperature, and the grain growth is dominated by a similar mechanism in undoped 3Y-TZP. The grain growth is more effectively retarded by the presence of a SiO2 phase above the eutectic temperature and is likely to be controlled by a solution-reprecipitation process in the amorphous phase at the grain-boundary corners or junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02591.x
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructural Analysis of Liquid-Phase-Sintered β-Silicon Carbide (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), 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: The microstructures of fine-grained β-SiC materials with α-SiC seeds annealed either with or without uniaxial pressure at 1900°C for 4 h in an argon atmosphere were investigated using analytical electron microscopy and high-resolution electron microscopy (HREM). An applied annealing pressure can greatly retard phase transformation and grain growth. The material annealed with pressure consisted of fine grains with β-SiC as a major phase. In contrast, the microstructure in the material annealed without pressure consisted of elongated grains with half α-SiC. Energy-dispersive X-ray analysis showed no differences in the amount of segregation of aluminum and oxygen atoms at grain boundaries, but did show a significant difference in the segregation of yttrium atoms at grain boundaries along SiC grains for the two materials. The increased segregation of yttrium ions at grain boundaries caused by the applied pressure might be the reason for the retarded phase transformation and grain growth. HREM showed a thin secondary phase of 1 nm at the grain boundary interface for both materials. The development of a composite grain consisting of a mixture of β/α polytypes during annealing was a feature common to both materials. The possible mechanisms for grain growth and phase transformation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00107.x
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  • 8
    Electronic Resource
    Electronic Resource
    Current-Voltage Characteristics across (0001) Twist Boundaries in Zinc Oxide Bicrystals (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), 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: Current-voltage (I–V) characteristics across (0001) twist boundaries with various misorientation angles were investigated in undoped ZnO bicrystals fabricated by a hot-joining technique. It was confirmed by high-resolution transmission electron microscopy that the boundaries were perfectly joined without intergranular phase. None of the bicrystals prepared in this study exhibited nonlinear I–V characteristics irrespective of coherency at the boundaries. Therefore, grain-boundary atomic configuration had no relation to the formation of double Schottky barriers at the (0001) twist boundaries in ZnO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00424.x
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of Interaction between Neighboring Oxygen Ions on Phase Stability in Cubic Zirconia (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), 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: The electronic structures of undoped c- and t-ZrO2 were calculated by a first-principles molecular orbital method. A preliminary analysis revealed that experimental energy-loss near-edge structure profiles obtained in ZrO2–8 mol% Y2O3 could be satisfactorily explained from the present theoretical calculation. The calculation suggests that the stability of t-ZrO2 could be described by the interaction between neighboring oxygen ions rather than the covalency of Zr—O bonds. The effect of dopant cations on the stability of cubic-zirconia solid solutions can be estimated semiquantitatively in terms of the repulsive Coulomb force between neighboring oxygen ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00495.x
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  • 10
    Electronic Resource
    Electronic Resource
    Superplastic Behavior of Fine-Grained β-Silicon Nitride Material under Compression (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), 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: The deformation behavior of a hot-pressed, fine-grained β-Si3N4 ceramic was investigated in the temperature range 1450°—1650°C, under compression, and the results for strain rate and temperature dependence of the flow stress are presented here. The present results show that the material is capable of high rates of deformation (∼10−4—10−3 s−1) within a wide range of deformation temperatures and under a pressure of 5—100 MPa; no strain hardening occurs in the material, even at slow deformation rates, because of its stable microstructure; Newtonian flow occurs, with a stress exponent of approximately unity; and the material has activation energy values for flow in the range 344—410 kJ·mol−1. Grain-boundary sliding and grain rotation, accommodated by viscous flow, might be the mechanisms of superplasticity for the present material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01283.x
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