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  • 1
    Electronic Resource
    Electronic Resource
    Use of the Retarded Solution-Reprecipitation Process to Attain a Higher Initial Permeability in MnZn Ferrites (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: We investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid-phase film during sintering. The solution-reprecipitation (S-R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid-phase film of critical thickness δo, which wets the MZF grains, is formed. The solid-state sintering that takes place before the formation of the continuous liquid-phase film is essential for the final microstructure of MZF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03522.x
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  • 2
    Electronic Resource
    Electronic Resource
    Anomalous Grain Growth in Donor-Doped Barium Titanate with Excess Barium Oxide (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: Grain growth and semiconductivity of donor-doped BaTiO3ceramics with an excess of BaO and additions of SiO2or B2O3were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO2or B2O3exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO3seed grains were embedded in a sample of donor-doped BaTiO3with an excess of BaO (without SiO2or B2O3), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO3and not NGG.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00146.x
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  • 3
    Electronic Resource
    Electronic Resource
    Positive Temperature Coefficient of Resistivity Effect in Highly Donor–Doped Barium Titanate (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: BaTiO3 ceramics doped with different La concentrations (0–12 mol%) were prepared by sintering under the reducing conditions of a nitrogen atmosphere containing 1% hydrogen. The critical donor concentration that causes blocking of the exaggerated grain growth was observed to be ∼10 mol% La. The samples, which were semiconducting after sintering under reducing conditions, were subsequently reoxidized by annealing in air to induce the positive temperature coefficient of resistivity (PTCR) effect. After reoxidation at 1150°C a noticeable PTCR effect was observed in the samples doped with La concentrations as high as 2.5 mol%. The room-temperature resistivity after reoxidation was found to increase with increasing donor concentration due to an increase in the thickness of the insulating layers at the grain boundaries. TEM analysis showed that reoxidation of the samples caused precipitation of the Ti-rich compound Ba6Ti17O40 inside the doped BaTiO3-matrix grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00828.x
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrothermal Synthesis of Manganese Zinc Ferrite Powders from Oxides (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: Manganese zinc (MnZn) ferrite powders were prepared via the hydrothermal treatment of a homogeneous mixture of the raw oxides (i.e., Fe2O3, ZnO, and Mn3O4 or MnO) at temperatures of 220°-320°C in air or an inert atmosphere. The final results of the hydrothermal reactions between the raw oxides were fine powders with a heterogeneous phase composition. In addition to lower concentrations of the residual reactants (Fe2O3, Mn3O4), two types of spinel-structure-based reaction products-ferrite ((Mn2+,Zn)Fe2O4) and manganate ((Zn,Mn2+)Mn23+O4)-were detected after the synthesis. The composition of the ferrite products, as well as the ratio of ferrite products to manganate products, were mainly functions of the oxidation state of the manganese that was present during treatment. The oxidation state of manganese during reaction was dependent on the valence of the manganese in the starting manganese oxide and on the atmosphere in the autoclave during reaction. When the hydrothermal reaction was conducted in air, almost-pure zinc ferrite was identified, whereas during reaction in an inert atmosphere, MnZn ferrite was formed. The kinetics of the hydrothermal reactions also were dependent on the oxidation state of manganese, as well as the temperature and specific surface area of the starting Fe2O3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01884.x
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  • 5
    Electronic Resource
    Electronic Resource
    Internal Oxidation of Ce3+-BaTiO3 Solid Solutions (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: The reoxidation process in highly Ce3+-doped BaTiO3 ceramics was studied using TEM. Samples of two different types of solid solutions, Ba1−XCe3+XTi1−X/4(VTi)X/4O3 and Ba1−XCe3+XTi4+1−XTi3+XO3, were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce3+ and Ti3+, fluorite CeO2 and monoclinic Ba6Ti17O40 phases were precipitated in the perovskite matrix. In Ba1−XCe3+XTi1−X/4(VTi)X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba1−XCe3+XTi4+1−XTi3+XO3 solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02789.x
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  • 6
    Electronic Resource
    Electronic Resource
    Fluorine as a Donor Dopant in Barium Titanate Ceramics (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: We have studied the electrical properties and microstructure of fluorine-doped BaTiO3 ceramics. The samples were prepared using a classical ceramic technology that involved the calcination of intimately mixed powders of BaCO3, TiO2, and BaF2. When the samples were sintered in untreated ambient air, the fluorine from the sample reacted with water vapor and formed gaseous HF. To prevent this hydrolysis of the fluorine, we sintered the samples in dried air. The fluorine-doped BaTiO3 ceramics sintered in a dry atmosphere showed microstructures and electrical properties typical of donor-doped BaTiO3. The samples containing up to 0.3 mol% of fluorine were coarse-grained, semiconducting, and displayed a remarkable PTCR effect. In contrast, the samples with a higher fluorine concentration were fine grained and insulating. A SIMS elemental mapping of the samples showed that the fluorine was distributed throughout the microstructure of the semiconducting samples; however, the fluorine concentration was enriched at grain boundaries and in the BaTi2O5 intergranular phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03327.x
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  • 7
    Electronic Resource
    Electronic Resource
    Solid Solubility of Neodymium in BaCeO3 (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: Incorporation of Nd into the BaCeO3 perovskite structure was studied by quantitative wavelength dispersive spectroscopy-electron probe microanalysis (WDS/EPMA) in combination with scanning electron microscopy (SEM) and X-ray powder diffractometry (XRPD). Highly Nd-doped BaCeO3 specimens, synthesized by mixed oxide technology, were sintered at 1400°C in ambient air. Concentrations of cations obtained by microanalysis were calculated to the ABO3 perovskite formula, considering incorporation of Nd at Ba as well as at Ce sites. Nd-BaCeO3 solid solutions may be represented by the general formula Ba1−XNdXCe1−YNdYO3−(Y-X)/2(VO)(Y-X)/2. The ratio between Nd incorporated at Ba sites and at Ce sites (X/Y) is a function of the starting composition, changing from 1 in the CeO2-rich part of the BaO-CeO2-Nd2O3 system, to ~0.1 in the BaO-rich part of the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03243.x
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  • 8
    Electronic Resource
    Electronic Resource
    Solid Solubility of Holmium, Yttrium, and Dysprosium in BaTiO3 (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: The solid solubility of R ions (R = Ho3+, Dy3+, and Y3+) in the BaTiO3 perovskite structure was studied by quantitative electron-probe microanalysis (EPMA) using wavelength-dispersive spectroscopy (WDS), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). Highly doped BaTiO3 samples were prepared using mixed-oxide technology including equilibration at 1400° and 1500°C in ambient air. The solubility was found to depend mainly on the starting composition. In the TiO2-rich samples a relatively low concentration of R incorporated preferentially at the Ba2+ lattice sites (solubility limit ∼Ba0.986R0.014Ti0.9965(V″Ti″)0.0035O3at 1400°C). In BaO-rich samples a high concentration of R entered the BaTiO3 structure at the Ti4+ lattice sites (solubility limit ∼BaTi0.85R0.15O2.925(VO••)0.075at 1500°C). Ho3+, Dy3+, and Y3+incorporated preferentially at the Ti4+ lattice sites stabilize the hexagonal polymorph of BaTiO3. The phase equilibria of the Ho3+–BaTiO3 solid solutions were presented in a BaO–Ho2O3–TiO2phase diagram.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07729.x
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  • 9
    Electronic Resource
    Electronic Resource
    Incorporation of Aliovalent Dopants into the Bismuth-Layered Perovskite-Like Structure of BaBi4Ti4O15 (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 solid solubility of the aliovalent dopants Fe3+ and Nb5+ in the BaBi4Ti4O15 compound, a member of the family of Aurivillius bismuth-based layer-structure perovskites, has been studied using quantitative wavelength-dispersive spectroscopic microanalysis (SEM/EPMA) in combination with X-ray powder diffractometry (XRPD). The samples with nominal (starting) compositions corresponding to the chemical formulas BaBi4Ti4–4XFe4XO15 and BaBi4Ti4–4XNb4XO15 were prepared by hot forging a mixture of BaTiO3 and Bi4Ti3O12 with additions of Fe2O3 or Nb2O5 followed by a long annealing at 1100°C. The study showed that an excess charge introduced into the structure by the substitution of Ti4+ ions with aliovalent dopants was preferentially compensated by a change in the ratio of Ba2+ to Bi3+ ions in the host structure according to the general formulas of the solid solutions Ba1–4XBi4+4XTi4–4XFe′4XO15 and Ba1+4XBi4–4XTi4–4XNb·4XO15.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01075.x
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of the Addition of Bi2O3 on the Grain Growth and Magnetic Permeability of MnZn Ferrites (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: Additions of Bi2O3 were used to promote grain growth and to increase magnetic permeability during sintering of MnZn ferrites. The results showed that small additions of Bi2O3 of 〈0.05 wt% remarkably increase the permeability of MnZn ferrites. On the other hand, addition of 0.05 wt% Bi2O3 induced the formation of a microstructure composed of giant grains with trapped pores embedded in a normal microstructure. The permeability of these samples showed a pronounced secondary maximum in permeability. At still higher Bi2O3 concentrations, above 0.2 wt%, the grain growth was retarded and a normal microstructure appeared; however, the magnetic permeability was strongly reduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02704.x
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