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  • 1
    Electronic Resource
    Electronic Resource
    Sintered alumina with low dielectric loss (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5895-5898 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low dielectric loss materials are required for applications in radio-frequency and microwave communications. Aluminium is the second most abundant element in the Earth's crust and aluminium oxide (alumina) is one of the commonest ceramics. Single crystals of aluminium oxide, i.e., sapphire, possess one of the lowest dielectric losses of any material. Polycrystalline alumina has a higher loss due to extrinsic factors. The dielectric loss of sintered alumina is studied in an attempt to determine the causes of extrinsic loss. Impurities are shown to play an important role, but the microstructure also is a key factor. High-purity aluminas, sintered to near theoretical density, are found to display very low loss, tan δ=2.7×10−5 at 10 GHz. Doping alumina with titanium dioxide was found to reduce the tan δ=2×10−5. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363584
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  • 2
    Electronic Resource
    Electronic Resource
    Integrated high-Tc multiloop magnetometer (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1418-1420 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two integrated, thin-film multiloop magnetometers (fractional turn SQUIDs) have been fabricated using a YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x multilayer process. The magnetometers have 16 parallel loops, an outer diameter of 7 mm and effective areas of 1.84 and 1.89 mm2, respectively. The magnetic field noise of the better device, measured in a YBCO tube at 77 K with a bias reversal scheme, was 37 fT Hz−1/2 at 1 Hz and 18 fT Hz−1/2 at 1 kHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113220
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization and Microwave Dielectric Properties of M2+Nb2O6 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: This paper details the investigation of the quality factor (Q), dielectric permittivity (ɛr) and temperature coefficient of resonant frequency (τf) of the TE01δ mode of the columbite binary niobate ceramics, with the formula MNb2O6 where M=2+ cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800° to 1400°C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M=Mn2+, Co2+, Ni2+, Cu2+, and Zn2+, and the group II metal cations M=Mg2+, Ca2+, Sr2+, and Ba2+. All columbite niobates were found to have ɛr between 17 and 22 and negative τf values between –45 and –76 ppm/°C, and ZnNb2O6, MgNb2O6, CaNb2O6, and CoNb2O6 had high Qf values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Qf of MgNb2O6 was found to rise to over 95 000 GHz when heated at 1300°C for 50 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00458.x
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  • 4
    Electronic Resource
    Electronic Resource
    Raman Spectroscopic Study of Gallium-Doped Ba(Zn1/3Ta2/3)O3 (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: Resonators of Ba(Zn1/3Ta2/3)O3, sintered between 1450° and 1600°C, are characterized by Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. The quality factors of the resonators are found to depend on sintering temperature, and at 1600°C there is evidence of Zn loss from the surface. The frequency of the A1g Raman mode changes from 800.9 cm−1 for a sample with Q= 80000 (2 GHz), to 794.5 cm−1 when Q= 44000 (2 GHz). Changes in the position of this and other Raman modes are thought to be due to distortions of the oxygen octahedra, brought about by Zn loss. The presence of a BaTa2O6 phase at the surface is confirmed by XRD and SEM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00348.x
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave Dielectric Loss of Titanium Oxide (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
    Notes: The dielectric loss (tan δ) of titanium dioxide (TiO2) disks has been measured at a frequency of 3 GHz. High-purity TiO2 sintered to almost-full density exhibits a very high tan δ, which is interpreted to be due to oxygen deficiency. To counter this, doping with stable divalent and trivalent cations, such as Mg and Al, leads to a low tan δ, probably by preventing Ti4+ reduction. The tan δ of polycrystalline TiO2 doped with divalent and trivalent ions with ionic radii in the range of 0.5–0.95 Å at 3 GHz can be very low: 6 × 10−5 (Q∼ 17 000) at a temperature of 300 K. The tan δ of undoped pure TiO2 disks increases when the disks are cooled from 300 K to ∼100 K. At temperatures 〈100 K, the tan δ decreases rapidly, which is interpreted as carrier freeze-out. The tan δ for all the high-Q doped TiO2 polycrystalline samples smoothly decrease to ∼5 × 10−6 (Q∼ 200 000) at 15 K, comparable to that of single crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01154.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of Doping on the Dielectric Properties of Cerium Oxide in the Microwave and Far-Infrared Frequency Range (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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07717_33.x
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  • 7
    Electronic Resource
    Electronic Resource
    Microwave Dielectric Properties of Gallium-Doped Hexagonal 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: High-permittivity and low-loss ceramics with composition BaTi0.92Ga0.08O2.96 have been prepared in the BaO–Ga2O3–TiO2 system using the mixed-oxide route. This compound forms as the hexagonal polymorph (6H) of BaTiO3 with the space group P63/mmc. The dielectric properties of dense ceramics have been studied, at microwave frequencies, with the ceramics fired at 1450°C under flowing oxygen gas; the results are a relative permittivity, ɛr, of ∼74 and a quality factor, Q·fr, of ∼7815 at 5.5 GHz. The quality factor is strongly influenced by the sintering conditions (temperature and atmosphere), whereas the relative permittivity is not influenced significantly by ceramic processing for pellets ≥93% of the theoretical X-ray density. To our knowledge, this is the first report of microwave dielectric resonance in a perovskite-type BaTiO3-based ceramic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03330.x
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  • 8
    Electronic Resource
    Electronic Resource
    Structure–Property Relations in xBaTiO3–(1−x)La(Mg1/2Ti1/2)O3 Solid Solutions (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 microwave dielectric properties and microstructures of compounds in the solid solution series xBaTiO3–(1−x)La(Mg1/2Ti1/2)O3 (BTLMT) have been investigated. The structural phase transitions that occur as a function of x have been studied and are related to changes in the dielectric properties. For compounds where x≤ 0.1, X-ray diffraction (XRD) showed evidence of 1:1 ordering between Mg and Ti cations. For x≤ 0.3, XRD and electron diffraction revealed that compounds were tilted in both antiphase and in-phase. However, for 0.3 〈 x 〈 0.7, only antiphase tilting was present. The temperature coefficient of resonant frequency (τf) vs the relative permittivity (ɛr) was linear until x= 0.5 at which point in the solid solution the transition to a nontilted structure resulted in nonlinear behavior. τf values close to zero (−2 ppm/°C) were achieved at x= 0.5 (ɛr∼ 60), which had a quality factor (Q·fo) of 9600 GHz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00584.x
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Porosity and Grain Size on the Microwave Dielectric Properties of Sintered Alumina (1997)
    Oxford, UK : Blackwell Publishing Ltd
    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 real part of the permittivity (ε) and the tan δ of sintered alumina (Al2O3) at about 9 GHz have been measured. The dielectric properties have been examined as a function of purity, pore volume, and sintered grain size. The tan δ is found to depend very strongly on the pore volume, purity, and grain size. ε is far less sensitive to impurities and grain size. The dependence of ε on porosity can be described by simple mixture models as expected. A model of losses in single crystals cannot be extended easily to these materials where extrinsic factors such as porosity, random crystal orientation, grain boundaries, microcracks, and impurities dominate. These factors have been studied in an attempt to describe the tan δ and ε of sintered polycrystalline alumina. In this work, the tan δ for alumina has been studied in near-theoretical density ranges between 9.1 times 10-5 and 2.4 times 10-5 depending on grain size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03066.x
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  • 10
    Electronic Resource
    Electronic Resource
    Surface resistance of thick film YBa2Cu3OX (1991)
    Weinheim : Wiley-Blackwell
    Advanced Materials 3 (1991), S. 318-320 
    Details
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/adma.19910030612
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