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  • 11
    Electronic Resource
    Electronic Resource
    Microstructural development of ZnO varistor during reactive liquid phase sintering (1996)
    Springer
    Journal of materials science 31 (1996), S. 5391-5398 
    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 The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) andin situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed ann value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159308
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  • 12
    Electronic Resource
    Electronic Resource
    Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method (2000)
    Springer
    Journal of materials science 19 (2000), S. 1457-1459 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011027624446
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  • 13
    Electronic Resource
    Electronic Resource
    A new interpretation for the degradation phenomenon of ZnO varistors (1992)
    Springer
    Journal of materials science 27 (1992), S. 5325-5329 
    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 The electrical degradation phenomena of zinc oxide-based varistors were studied using a high-energy current pulse and a.c. polarization at different temperatures. Activation energy measurements during the degradation process showed that these phenomena are associated with diffusion and that the diffusion-controlling species are slower than Zn., For degradation promoted by current pulses of 8×20 μs, the Schottky potential barrier deformation was measured. A decrease in height and width of the potential barrier due to the reduction of surface states density,N s, without a significant change in donor density,N d, was observed. To explain these results, a modification of the unstable components model is proposed for the potential barrier in which the degradation is due to oxi-reduction reactions between atomic defects. These reactions promote the elimination of zinc vacancies and/or adsorbed oxygen on the grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02403838
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  • 14
    Electronic Resource
    Electronic Resource
    A new interpretation for the degradation phenomenon of ZnO varistors (1992)
    Springer
    Journal of materials science 27 (1992), S. 5325-5329 
    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 The electrical degradation phenomena of zinc oxide-based varistors were studied using a high-energy current pulse and a.c. polarization at different temperatures. Activation energy measurements during the degradation process showed that these phenomena are associated with diffusion and that the diffusion-controlling species are slower than Zn., For degradation promoted by current pulses of 8×20 μs, the Schottky potential barrier deformation was measured. A decrease in height and width of the potential barrier due to the reduction of surface states density,N s, without a significant change in donor density,N d, was observed. To explain these results, a modification of the unstable components model is proposed for the potential barrier in which the degradation is due to oxi-reduction reactions between atomic defects. These reactions promote the elimination of zinc vacancies and/or adsorbed oxygen on the grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553413
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  • 15
    Electronic Resource
    Electronic Resource
    The effect of heating rate on the sintering of agglomerated NaNbO3 powders (1998)
    Springer
    Journal of materials science 33 (1998), S. 4791-4795 
    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 The effect of heating rate on the sintering of agglomerated NaNbO3 powders, processed by the polymeric precursors method, was studied. The results showed that the presence of agglomerated powder leads to a heterogeneous microstructure, with bimodal grain size distribution, after sintering. Using a high heating rate, the sintering of agglomerated particles was inhibits, leading to a homogeneous microstructure, with single grain size distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004422111613
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  • 16
    Electronic Resource
    Electronic Resource
    High dielectric constant of SrTiO3 thin films prepared by chemical process (2000)
    Springer
    Journal of materials science 35 (2000), S. 4783-4787 
    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 SrTiO3 thin films were prepared by the polymeric precursor method and deposited by spin-coating onto Pt/Ti/SiO2/Si(100) substrates. The spin-coated films heat treated at 700°C were crack-free, dense, and homogeneous. Microstructural and morphological evaluations were followed by grazing incident X-ray, scanning electron microscopy and atomic force microscopy. Dielectric studies indicated a dielectric constant of about 475, which is higher than that of ceramic SrTiO3, and a factor dissipation of about 0.050 at 100 kHz. SrTiO3 thin films were found to have paraelectric properties with C-V characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004816611050
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  • 17
    Electronic Resource
    Electronic Resource
    Experimental and theoretical study on the piezoelectric behavior of barium doped PZT (1999)
    Springer
    Journal of materials science 34 (1999), S. 3659-3667 
    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 An experimental and theoretical study of the ferroelectric and piezoelectric behavior of PZT doped with barium is presented. Ab initio perturbed ion calculations was carried out. The properties, such as remnant polarization, coercive field and the coupling factor of the PZT at constant sintering temperature was compared with the Zr4+/Ti4+ ions dislocation energy and the lattice interaction energy. An agreement between the experimental and theoretical results, with a decrease of the interaction energy and an inversion of the energy stability from tetragonal to rhombohedral phase was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004647204505
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  • 18
    Electronic Resource
    Electronic Resource
    An ab initio study of oxygen vacancies and doping process of Nb and Cr atoms on TiO2 (110) surface models (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 65 (1997), S. 625-631 
    Details
    ISSN: 0020-7608
    Keywords: ab initio ; oxygen vacancy ; doping ; titanium oxide surface ; varistor ceramics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We theoretically investigated how the formation of oxygen vacancies and the addition of niobium and chromium atoms as dopants modify the varistor properties of TiO2. The calculations were carried out at the HF level using a contracted basis set, developed by Huzinaga et al., to represent the atomic centers on the (110) surface for the large (TiO2)15 cluster model. The change of the values for the net atomic charges and band gap after oxygen vacancy formation and the presence of dopants in the lattice are analyzed and discussed. It is shown that the formation of oxygen vacancies decreases the band gap while an opposite effect is found when dopants are located in the reduced surface. The theoretical results are compared with available experimental data. A plausible explanation of the varistor behavior of this system is proposed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 625-631, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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