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  • 1
    Electronic Resource
    Electronic Resource
    Nanoscale Imaging of CaCu〈sub〉3〈/sub〉Ti〈sub〉4〈/sub〉O〈sub〉12〈/sub〉 Dielectric Properties: The Role of Surface Defects (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 131-133 (Oct. 2007), p. 443-448 
    Details
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: Scanning probe microscopy with conductive tips has been used to image the dielectricproperties of ceramics with giant permittivity. In particular, measurements in impedance mode andof local resistivity allowed to image the permittivity map on polycrystalline materials. Such imagingallows to correlate the dielectric properties with the local sample structure and with defects insidethe single grains of the polycrystalline ceramics. However, artifacts due to surface imperfectionsshould be distinguished from bulk properties and eliminated
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/24/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.131-133.443.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructural and Electrical Characterisation of La〈sub〉x〈/sub〉Ba〈sub〉1-x〈/sub〉Ti〈sub〉1-x〈/sub〉Y〈sub〉x〈/sub〉O〈sub〉3〈/sub〉 (0≦ x≦ 0.50) Ceramics (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 873-876 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: LaxBa1-xTi1-xYxO3 (0≤x≤0.5) powders were synthesised in air at 1400°C by theconventional solid state method. According to the X-ray results, the tetragonal distortion in undoped(x=0) BaTiO3 (space group P4mm) decreases with x and samples with x ≥0.05 show cubicsymmetry (space group Pm3m). For x≥0.05, the lattice parameter increases linearly with x, untilorthorhombic LaYO3 appears as a secondary phase for x〉0.45. Dielectric properties of dense(〉95% of the theoretical X-ray density) ceramics were studied at both radio and microwavefrequencies. The permittivity maximum is shifted towards lower temperatures with increasing x anda broad permittivity peak is observed for samples with 0.05〈x〈0.30. These samples exhibit adielectric response typical of “relaxor”-type materials. In contrast, ceramics with x=0.40 exhibitalmost temperature independent dielectric properties (τf=+12 ppm/K) and although they resonate atmicrowave frequencies they have low quality factors (Q.f≤ 755 at ~5 GHz). Finally, conventionaltransmission electron microscopy combined with electron diffraction studies were carried out toprovide a better understanding of structure-property relationships in LaxBa1-xTi1-xYxO3 ceramics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/51/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.317-318.873.pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Structure–Property Relationships of BaTi1−2yGayNbyO3 (0≤y≤0.35) Ceramics (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: BaTi1−2yGayNbyO3 (BTGN) (0≤y≤0.35) powders were synthesized at 1300°C by the conventional solid-state method. Room temperature x-ray diffraction patterns for y≤0.025 and 0.05≤y≤0.30 can be indexed as the tetragonal (P4mm) and cubic (Pm 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00580:JACE_00580_mu1" location="equation/JACE_00580_mu1.gif"/〉 m) polymorphs of BaTiO3, respectively, whereas y=0.35 consists of a mixture of the cubic polymorph of BaTiO3 and an 8H hexagonal-type perovskite (P63/mcm) isostructural with Ba8Ti3Nb4O24. Scanning electron microscopy shows the microstructures of BTGN ceramics (y≤0.30) sintered at 1500°C to consist of fine grains (1–3 μm) within a narrow grain size and shape distribution. Room temperature transmission electron microscopy for y≤0.08 reveals core–shell structures and (111) twins in some grains; however, their relative volume decreases with y. Energy dispersive spectroscopy reveals the cores to be Ga and Nb deficient with respect to y. For y〉0.08 there is no evidence of core–shell structures, however, some grains have a high density of dislocations, consistent with chemical inhomogeneity. BTGN ceramics exhibit a diverse range of dielectric behavior in the temperature range 120–450 K and can be subdivided into two groups. 0.025≤y≤0.15 display modest ferroelectric relaxor-type behavior, with high room temperature permittivity, ɛ25′, (〉300 at 10 kHz), whereas 0.25≤y≤0.30 are temperature and frequency stable dielectrics with ɛ25′〈100 that resonate at microwave frequencies with modest quality factors, Q×f, ∼3720 GHz (at ∼5 GHz) for y=0.30.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00580.x
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  • 4
    Electronic Resource
    Electronic Resource
    BaTiO3-Based Ceramics for Tunable Microwave Applications (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 dielectric properties of BaTi0.90Ga0.05Nb0.05O3 (BTGN) and Ba0.60Sr0.40TiO3 (BST) ceramics prepared by the conventional solid-state route have been investigated. Their relative potential for microwave (MW) tunable applications was assessed by the figure of merit (K) defined as K = [equation omitted] (where [alt epsilon]ro and [alt epsilon]rv are the relative permittivity at zero and 20 kV cm−1 at 10 kHz and tan δo is the loss at 10kHz or ∼1 GHz without DC bias). Fine-grained (∼2–3 μm) BTGN ceramics fired at 1500°C in air exhibit dielectric behavior characteristic of relaxor-type materials, with relative permittivity, [alt epsilon]r, decreasing from ∼3082 to ∼2116 and dielectric loss, tan δ, increasing from 0.0035 to 0.0542 at 10 kHz and ∼1GHz, respectively. In contrast, large-grained (20–100 μm) BST ceramics exhibit a frequency independent [alt epsilon]r of ∼5000 and show little variation of tan δ with frequency (0.0012 at 10 kHz and ∼0.0048 at 0.6 GHz). At 10 kHz, KBTGN= 91 and KBST= 367, whereas at MW frequencies KBTGN= 6 and KBST= 92. The large decrease in KBTGN at MW frequencies is attributed to a substantial increase of tan δ. The applicability of another relaxor-type BaTiO3-based ceramic, Ba(Ti0.70Zr0.30)O3, which was recently proposed as promising material for tunable MW applications, is also discussed. It is demonstrated that BaTiO3-based ferroelectric-relaxors may exhibit good tunable characteristics at 10 kHz; however, they are not competitive with BST for high K-factor MW applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01082.x
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  • 5
    Electronic Resource
    Electronic Resource
    Insulating Properties of Lanthanum-Doped BaTiO3 Ceramics Prepared by Low-Temperature Synthesis (2004)
    Oxford, UK : Blackwell Publishing Ltd
    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: Samples of composition Ba1−xLaxTi1−x/4O3, x= 0, 0.003, 0.03, and 0.10, were prepared by an alkoxide sol–gel route with final firing of ceramics at 1100°C, 2 h in air. All samples showed bulk insulating behavior with no evidence of semiconductivity caused by either direct donor doping or oxygen loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb06370.x
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical and structural characteristics of lanthanum-doped barium titanate ceramics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6355-6366 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single phase La-doped BaTiO3 with the formula Ba1−xLaxTi1−x/4O3: 0≤x≤0.20 was prepared by solid state reaction of oxide mixtures at 1350 °C, 3 days, in O2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x≥0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x∼0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from ∼10 000 for x=0 at 130 °C to ∼25 000 for x=0.06 at ∼−9 °C. At larger x, the permittivity maximum broadened, showed "relaxor"-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371698
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  • 7
    Electronic Resource
    Electronic Resource
    CaCu3Ti4O12: One-step internal barrier layer capacitor (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2153-2155 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There has been much recent interest in a so-called "giant-dielectric phenomenon" displayed by an unusual cubic perovskite-type material, CaCu3Ti4O12; however, the origin of the high permittivity has been unclear [M. A. Subramanian, L. Dong, N. Duan, B. A. Reisner, and A. W. Sleight, J. Solid State Chem. 151, 323 (2000); C. C. Homes, T. Vogt, S. M. Shapiro, S. Wakimoto, and A. P. Ramirez, Science 293, 673 (2001); A. P. Ramirez, M. A. Subramanian, M. Gardel, G. Blumberg, D. Li, T. Vogt, and S. M. Shapiro, Solid State Commun. 115, 217 (2000)]. Impedance spectroscopy on CaCu3Ti4O12 ceramics demonstrates that they are electrically heterogeneous and consist of semiconducting grains with insulating grain boundaries. The giant-dielectric phenomenon is therefore attributed to a grain boundary (internal) barrier layer capacitance (IBLC) instead of an intrinsic property associated with the crystal structure. This barrier layer electrical microstructure with effective permittivity values in excess of 10 000 can be fabricated by single-step processing in air at ∼1100 °C. CaCu3Ti4O12 is an attractive option to the currently used BaTiO3-based materials which require complex, multistage processing routes to produce IBLCs of similar capacity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463211
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  • 8
    Electronic Resource
    Electronic Resource
    An Alternative Explanation for the Origin of the Resistivity Anomaly in La-Doped BaTiO3 (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: Semiconductivity in La-doped BaTiO3 ceramics after high-temperature firing, e.g., 1350°C in air, is attributed to oxygen nonstoichiometry. In more heavily doped compositions, the observed resistivity rise is attributed to surface oxidation of the grains during cooling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00684.x
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  • 9
    Electronic Resource
    Electronic Resource
    Development of an Equivalent Circuit Model for Cement Pastes from Microstructural Considerations (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 general approach to equivalent circuit modeling of cement pastes has been to interpret spectra obtained from ac impedance measurements, assigning electrical responses to microstructural features such as hydration products and fluid-filled porosity. In this paper, we take an alternative approach. Starting with a consideration of paste microstructures and the potential conduction pathways that such microstructures could support, we propose an equivalent circuit model. Ac impedance data from pore-reduced cements have been measured for the first time and are used to test the model. This approach has permitted estimation of conductivities of in situ pore fluid, which we believe to be influenced by hydrogen bonding to varying extents depending on pore size, and hydration product. Preliminary results are in broad agreement with data obtained by alternative methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03206.x
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of Lanthanum-Doped Barium Titanate Ceramics Using Impedance Spectroscopy (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 electrical properties of two single-phase, lanthanum-doped BaTiO3 compositions, x= 0.03 and x= 0.20, in Ba1–xLaxTi1–x/4O3 were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C. Samples heated in oxygen were electrically insulating, whereas those heated in argon lost oxygen and were semiconducting at room temperature, irrespective of x. Samples heated in air showed intermediate electrical properties and also were electrically inhomogeneous; the two compositions showed different electrical behaviors, and a model for each, based on oxygen nonstoichiometry within the ceramics, is proposed. Oxygen deficiency in samples sintered in air was avoided by heating at 1200°C, instead of 1350°C. Alternatively, oxygen lost from ceramics heated in air at 1350°C was regained by postannealing in oxygen at 1350°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00694.x
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