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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of α-SiAlON Seed Crystals (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: Single-phase seed crystals of Ca- and Y-α-SiAlONs have been synthesized for tailoring microstructure of α-SiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for α-SiAlON seed preparation and morphology control are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00894.x
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  • 2
    Electronic Resource
    Electronic Resource
    Reply to “Comment on ‘Morphology of Silicon Nitride Grown from a Liquid Phase’” (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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01257.x
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  • 3
    Electronic Resource
    Electronic Resource
    Solution Mechanisms for Dopant Oxides in Yttria (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), 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: Solution mechanisms in Y2O3 have been studied by using atomistic simulation. Various defect reactions for the solution of A2+, M3+, and B4+ ions, assuming either single isolated impurities or defect clusters, have been considered. Generally, the radius of the dopant cation is an important factor in determining the solution site and cluster geometry, and it can be critical in deciding the solution mechanism. Mechanisms that are associated with codoping A2+ and B4+ ions also have been considered. Surprisingly, this action does not always result in a reduction in the solution enthalpy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01954.x
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  • 4
    Electronic Resource
    Electronic Resource
    Model for Fatigue Crack Growth in Grain-Bridging Ceramics (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), 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: A model for fatigue crack propagation based on sliding wear of bridging grains is analyzed for polycrystalline ceramics. Taking into account damage development and crack tip energy balance, we have obtained rigorous solutions for equilibrium and compatibility equations in the crack wake under monotonic and cyclic loading/unloading conditions. Fatigue mechanics in ceramics is found to be formally similar to elastic-plastic mechanics of a path-dependent hardening material, due to the frictional resistance to reverse sliding. It features a load-displacement hysteresis causing energy dissipation and wear, and a longer cohesive zone required for supporting the same peak load with the wear-reduced bridging stresses. The unloading crack opening displacement is more strongly dependent on Kmax than on DeltaK; such displacement causes wear on the bridging grains. Meanwhile, incremental crack growth brings in new bridging grains that has a shielding effect on the crack tip stress field; such an effect is strongly dependent on Kmax but independent of DeltaK. At steady state, when shielding accumulation and shielding degradation are balanced, the fatigue crack growth rate has a form da/dN=A(Kmax)b(DeltaK)c, where A, b, and c are material-dependent parameters. Fatigue is predicted to have a very high b, a modest c, a higher fatigue resistance for tougher ceramics, and a stronger Kmax dependence for less tough ceramics. These predictions are in agreement with experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02278.x
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  • 5
    Electronic Resource
    Electronic Resource
    Sintering of Fine Oxide Powders: II, Sintering Mechanisms (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: Conventional and new sintering mechanisms have been investigated using fine powders of CeO2 and Y2O3 of excellent sinterability. We have verified the validity of Herrings scaling law for 60%–84% relative density and found that it is consistent with grain-boundary-diffusion control. At lower densities, we have found that pores larger than the critical size, in the sense of Kingery and Francois, can still be sintered readily. This is rationalized by a new sintering mechanism based on particle repacking concurrent with particle coarsening, resulting in a higher packing factor. Very fine, surface-active powders that coarsen rapidly are uniquely capable of taking advantage of this new sintering mechanism, which along with their propensity to homogenization, accounts for their remarkable sinterability even at very low green densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02879.x
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  • 6
    Electronic Resource
    Electronic Resource
    Model experiments on fatigue of Pb(Zr0.53Ti0.47)O3 ferroelectric thin films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1923-1925 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With an n-type or p-type semiconductor as a top electrode in contact with ferroelectric Pb(Zr0.53Ti0.47)O3 thin film, polarization fatigue has been studied to investigate the effect of charge carrier injection. Electron injection is shown to be correlated with fatigue while hole injection is not. Current blocking by an insulating SiO2 layer prevents fatigue as well. The enhanced mobility of oxygen vacancies, partially de-ionized by association with the injected electrons, is proposed to be the mechanism for the electron effect.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121228
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  • 7
    Electronic Resource
    Electronic Resource
    Fatigue of Pb(Zr0.53Ti0.47)O3 ferroelectric thin films (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7789-7798 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fatigue of Pb(Zr0.53Ti0.47)O3 ferroelectric thin films has been studied with several novel electrode modifications. Doped amorphous silicon is used as a gating layer between the ferroelectric and metal electrode to regulate the type of charge carrier injection during switching of the ferroelectric. This configuration requires a low switching frequency in order to avoid the relaxation effect that arises from the limited charging ability of the semiconductor. In addition, charge depletion in the semiconductor causes a polarization asymmetry that reflects a depolarization field due to incomplete compensation of the polarization charge. Fatigue tests reveal that electron injection is a necessary condition for polarization degradation, whereas hole injection is not. Blocking interfaces by SiO2 or c-oriented Bi4Ti3O12 can also mitigate fatigue, albeit at a reduced polarization level. On the other hand, compensation of Pb loss through PbO undercoat layer has little effect on fatigue. Based on these observations, injected electrons in association with oxygen vacancies generated during cycling are proposed as the defects responsible for fatigue. These defects may impede domain switching by segregation at the electrode interface or at domain boundaries, with an enhanced kinetics because of the lower valence of the partially de-ionized entity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367953
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  • 8
    Electronic Resource
    Electronic Resource
    Activation field and fatigue of (Pb, La)(Zr, Ti)O3 thin films (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 4186-4188 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a class of (Pb, La)(Zr, Ti)O3 ferroelectric thin films, the Merz equation adequately describes the dynamics of switching resistance. A single parameter, activation field, can be used to relate the coercive field throughout the polarization fatigue process. We suggest that the increased switching resistance causes fatigue, and that it could originate from the dielectric degradation of the film. The constitutive equation for the coercive field and its correlation with the switchable polarization offer a tool for fatigue characterization and life prediction. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125577
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  • 9
    Electronic Resource
    Electronic Resource
    Formation of β-Silicon Nitride Crystals from (Si,Al,Mg,Y)(O,N) Liquid: II, Population Dynamics and Coarsening Kinetics (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: Precipitation, growth, and coarsening of Si3N4 crystals in (Si,Al,Mg,Y)(O,N) liquids at 1680°C has been studied. Contrary to the common observation in kinetics, coarsening rates of crystals in length and width are found to accelerate when the total volume of crystals remains little changed. This is attributed to the concomitant β-Si3N4 to β′-SiAlON transformation, which introduces an additional driving force for crystal dissolution and reprecipitation. As a result of the additional driving force, which has a nonmonotonic size dependence, the normalized size distribution is expected to evolve with time, initially broadening, then shifting skewing as the transformation passes the midpoint, and finally converging to a sharp distribution as the transformation completes. These evolutions have been observed in all the compositions studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03518.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of Seeding on the Microstructure and Mechanical Properties of α-SiAlON: III, Comparison of Modifying Cations (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: Single-phase in situ toughened SiAlON ceramics containing various modifying cations and single-crystal seeds were studied. The modifying cations include rare-earth cations from the smallest to the largest allowed in the α-SiAlON structure (Yb to Y, to Nd), and from monovalent to trivalent (Li to Ca, to rare earths). At low seeding levels, the aspect ratio of grains increases with the size of modifying cations, giving rise to rather different appearances of the microstructure in different SiAlONs. A one-to-one correspondence between seed crystals and large grains at low seeding levels is also observed. An optimal amount of seeds is required to maximize the fracture toughness, which is controlled by grain pullout with the fracture energy that scales with the fraction of elongated grains, their width, and their aspect ratio. The optimal amount of seeds required to reach maximal toughening increases with the aspect ratio of grains and is the lowest (1%) in Y- and Yb-SiAlONs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03443.x
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