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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 147-150 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phenomenon of electrical degradation in ZnO varistors was studied by application of high-intensity current pulses. A wave shape of 8×20 μs and rectangular waves of 1 and 2 ms were used. The degradation was estimated by reference electric-field variation and by Schottky voltage barrier deformation. The results showed that current pulses reduce both the height and the width of the barrier voltage. It was also observed that the donor density Nd did not change but the surface states density Ns decreased with degradation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6545-6548 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical characteristics of highly dense SnO2 ceramic varistors are believed to be caused by the existence of potential barriers at the grain boundary. A complex plane analysis technique (to eliminate the influence of trapping activity associated with the conductance term observed via depression angle of a semicircular relaxation in the complex capacitance plane), allied with an approached Mott–Schottky model, are used to demonstrate that the potential barriers at the grain boundary are Schottky-type barriers in SnO2 varistors such as those observed in the traditional ZnO varistor. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5972-5978 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Barium strontium titanate (Ba0.8Sr0.2TiO3) thin films have been prepared on Pt/Ti/SiO2/Si substrates using a soft solution processing. X-ray diffraction and also micro-Raman spectroscopy showed that the Ba0.8Sr0.2TiO3 thin films exhibited a tetragonal structure at room temperature. The presence of Raman active modes was clearly shown at the 299 and 725 cm−1 peaks. The tetragonal-to-cubic phase transition in the Ba0.8Sr0.2TiO3 thin films is broadened, and suppressed at about 35 °C, with a maximum dielectric constant of 948 (100 kHz). Electrical measurements for the prepared Ba0.8Sr0.2TiO3 thin films showed a remnant polarization (Pr) of 6.5 μC/cm2, a coercive field (Ec) of 41 kV/cm, and good insulating properties. The dispersion of the refractive index is interpreted in terms of a single electronic oscillator at 6.97 eV. The direct band gap energy (Eg) and the refractive index (n) are estimated to be 3.3 eV and n = 2.27–2.10, respectively. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 6007-6014 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article describes the admittance-frequency feature of a class of SnO2⋅CoO-based polycrystalline ceramics with high nonlinear current–voltage characteristics (nonlinear coefficients above 50). Broad relaxation peaks caused by the presence of deep trap states were characterized based on the admittance response of different systems doped with La2O3, Pr2O3, and CeO2. The calculation of the energy of this deep trap level revealed not only that all the compositions share the same value but also that this value could be attributed to an oxygen vacancy or to CoSn[partial lengthening] like defects. The values of barrier height and density of states obtained from a capacitance–voltage analysis are in good agreement with the nonlinear coefficients. The highest nonlinear coefficients are found in compositions with greater barrier height values and higher density of deep trap states at the grain boundary interface. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 48-50 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model is proposed here to explain how the chemical features of metal oxide varistors can alter their nonohmic physical behavior, based on nonohmic similarities in the electrical properties of ZnO- and SnO2-based varistors. The proposed model explains the electrical properties of ZnO- and SnO2-based varistors before and after thermal treatments in oxygen- and nitrogen-rich atmospheres, which cause similar changes in the nonohmic feature of these polycrystalline ceramics with greatly differing chemical compositions and microstructures. The model is based on the key role that oxygen plays in varistor grain boundaries, independently of the type of ceramic system (ZnO-, SnO2- or even SrTiO3-based varistors) involved. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2148-2150 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter reports on a process to prepare nanostructured PbTiO3 (PT) at room temperature with photoluminescence (PL) emission in the visible range. This process is based on the high-energy mechanical milling of ultrafine PbTiO3 powder. The results suggest that high-energy mechanical milling modifies the particle's structure, resulting in localized states in an interfacial region between the crystalline PT and the amorphous PT. These localized states are believed to be responsible for the PL obtained with short milling times. When long milling times are employed, the amorphous phase that is formed causes PL behavior. An alternative method to process nanostructured wide-band-gap semiconductors with active optical properties such as PL is described in this letter. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2433-2435 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric properties of (Ba, Sr)TiO3 films were found to be remarkably sensitive to the postannealing treatment atmosphere. This study demonstrates that postannealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that postannealing in a nitrogen atmosphere produces a slight dielectric relaxation. Such dependence of the dielectric relaxation was related both to oxygen vacancies and to the presence of negatively charged oxygen, trapped at the grain boundary and/or at the electrode/dielectric film interface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    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 phase evolution of lead titanate processed by the polymeric precursor method was investigated by thermal analysis, X-ray diffraction, and high-resolution transmission electron microscopy. The results showed that the cubic perovskite PbTiO3 (PT) phase is formed from an inorganic amorphous precursor at a temperature of 444°C. A gradual transition from cubic to tetragonal perovskite PT was observed with the increase of calcination time at this temperature. HRTEM results showed that the cubic PT particles have a size of around 5 nm. The identification of cubic PT as an intermediate phase supports the hypothesis that the chemical homogeneity was kept at the molecular level during the synthesis process, with no cation segregation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    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 performed a comparative study of electrical and thermal properties of ZnO- and SnO2-based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO2-based varistor system. In spite of this, the SnO2 showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant concentration is a remarkable result that point out to the use of this system to compete commercially with ZnO-based varistor devices.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The non-ohmic properties of the 98.95% SnO2 + 1.0%,CoO + 0.05%,Nb2O5 (all in mole%) system, as well as the influence of sintering temperature and atmosphere on these properties, were characterized in this study. The maximum non-linear coefficient (α = 32) was obtained for a sintering temperature of 1300°C in an oxygen atmosphere and this maximum is associated with the presence of O in SnO2 grain boundaries, as interface defects. Experimental results also indicate thermionic-type conduction mechanisms, which are associated with the potential barrier of Schottky or Poole–Frenkel types.
    Type of Medium: Electronic Resource
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