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  • 1
    Electronic Resource
    Electronic Resource
    Structural characteristics of Sr1−xLaxTi3+δ as a function of oxygen partial pressure at 1400 °C (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1492-1498 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural characteristics of Sr1−x Lax TiO3+δ (0≤x≤0.4) at 1400 °C have been investigated as a function of ambient oxygen partial pressure. A modified Rietveld pattern-fitting structure-refinement program [H. M. Rietveld, J. Appl. Crystallogr. 2, 65 (1969)] was used to determine the nature of the distortions of the fundamental perovskite unit cell, the degree of lattice perfection, and the cation vacancy concentrations. Specimens equilibrated in forming gas displayed a linear relation between x, the lattice parameters, and the degree of lattice perfection while those samples annealed in air and oxygen deviated significantly from linearity. A monoclinic distortion of the perovskite structure was seen in the samples at low oxygen partial pressures while a second phase or layer type of distortion appeared in samples with x〉0.2 under oxidizing conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342963
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  • 2
    Electronic Resource
    Electronic Resource
    Optical properties of CeO2 films prepared from colloidal suspension (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2517-2521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption of nanocrystalline thin films can be influenced by the presence of both porosity and grain size effects. If both are present simultaneously, their effects are difficult to separate. In this study it is shown that the combination of uv-vis transmittance and reflectance measurements on porous CeO2 films provides enough data to make this separation. The CeO2 films were prepared by deposition of nanosized (∼5 nm) particles from a water colloidal suspension onto sapphire and subjecting these films to sintering temperatures sufficiently high to provide a series of films with a typical thickness of 0.6 μm with a wide range of grain sizes and porosity. X-ray diffraction, scanning electron microscopy, ellipsometry, and profilometry were used to characterize the films and to compare the observed grain sizes and porosity with that obtained from optical measurements. All of the techniques used gave results on porosity and grain size which were in good agreement, from 15% to 50% and 5 to 65 nm, respectively. For these porous films it was found that the changes in absorption which are normally explained by quantum confinement effects due to the small crystallite size can be attributed primarily to changes in porosity rather than in grain size. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1389329
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  • 3
    Electronic Resource
    Electronic Resource
    Thermal expansion and the high–low transformation in quartz. II. Dilatometric studies (1974)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 7 (1974), S. 468-473 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Thermal expansion and contraction of single-crystal quartz, 400 mesh quartz powder, and chert were measured with a highly sensitive dilatometer apparatus. Below 560°C expansion characteristics were identical and in agreement with X-ray diffractometer measurements. Between 571 and 573°C single-crystal quartz expanded with a volume coefficient of 250 × 10−5 deg−1 and exhibited 2.5°C hysteresis. Between 571 and 576°C 400 mesh quartz expanded with a volume coefficient of 150 x 10−5 deg−1 and exhibited 1°C hysteresis. Chert expanded more gradually between 560 and 650°C, with a maximum volume coefficient of 31 × 10−5 deg−1 and exhibited no hysteresis. The results are interpreted in terms of a Dauphiné twinning mechanism and related to observations from the literature, particularly those relating to light-scattering phenomena and strength measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889874010223
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and phase transformation of lanthanum chromate (1996)
    Springer
    Journal of materials science 31 (1996), S. 551-557 
    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 Lanthanum chromate (LaCrO4) was synthesized as a low temperature ( 〈 700 °C) intermediate to perovskite-type, lanthanum chromite (LaCrO3). The lattice parameters, atom positions and bond lengths determined from X-ray powder diffraction show that LaCrO4 forms a monazite-type crystal structure. Lanthanum chromate forms a solid solution with Ca, having a solubility between 10 and 20 at%. Thermal analysis shows that at ambient oxygen pressure, LaCrO4 transforms to LaCrO3 at a temperature near 700 °C. It also indicates that (La,Ca)CrO4 initially transforms to LaCrO3 and CaCrO4 with the subsequent formation of a (La,Ca)CrO3 solid solution. Evidence of Ca segregation to the surface of (La,Ca) CrO3 particles is given by Auger electron spectroscopy and scanning electron microscopy.[/p]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01139176
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  • 5
    Electronic Resource
    Electronic Resource
    Electrical conductivity and Seebeck coefficient of (La, Ca) (Cr, Co)O3 (1992)
    Springer
    Journal of materials science 27 (1992), S. 5477-5482 
    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 Electrical conductivity and Seebeck coefficients of (La, Ca) (Cr, Co)O3 were measured as a function of temperature. The electrical conductivity as measured in air from 100 to 1100 °C increased with increasing Co and Ca content. The Seebeck coefficients were positive, indicating p-type conductivity. The substitution of Co for Cr significantly decreased the Seebeck coefficients, indicating that the substitution resulted in an increase in site occupancy, associated with the Co. The additional Ca substitution for La resulted in further decrease in the Seebeck coefficients, then exhibited a temperature-independent behaviour, indicating that the carrier mobility, rather than carrier concentration, was thermally activated. The activation energies were 0.18 and 0.25 eV for LaCrO3 and LaCoO3, respectively, and increased to about 0.50 eV with substitution of 10 mol% Co for Cr and then linearly decreased as Co content increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00541609
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  • 6
    Electronic Resource
    Electronic Resource
    Investigation of strontium-doped La(Cr, Mn)O3 for solid oxide fuel cells (1992)
    Springer
    Journal of materials science 27 (1992), S. 5837-5843 
    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 (La, Sr) (Cr, Mn)O3 system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O3 system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2–20 S cm−1 for LaCr0.8Mn0.4O3 and La0.9Sr0.1Cr0.2Mn0.8O3, respectively. All of the compositions showed similar dependence of electrical conductivity on the oxygen activity. Dependence was small at high oxygen activities; as the oxygen activity decreased, a break in electrical conductivity at 10−12 atm and 1000°C was observed, and then the electrical conductivity decreased asP O2 1/4 . Sintering and electrical conductivity studies indicate that La0.9Sr0.1Cr0.2Mn0.8O3 appears to be a candidate for solid oxide fuel cell applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01119747
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  • 7
    Electronic Resource
    Electronic Resource
    Liquid phase behaviour in nonstoichiometric calcium-doped lanthanum chromites (1996)
    Springer
    Journal of materials science 31 (1996), S. 157-163 
    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 sinterability of (La,Ca)CrO3 is analysed by comparing the liquid phase behaviour in A-site excess and A-site deficient compositions (referring to the ABO3 formula). The analysis shows that a series of A-site excess and deficient compositions form distinct liquid phases belonging to the CaO-Cr2O3 phase system. Although both series experience grain growth and densification due to the presence of a liquid phase, the A-site excess compositions exhibit greater shrinkage and sinter to closed porosity, whereas the A-site deficient compositions remain porous. During the final stages of sintering, surplus liquid from the A-site excess material exudes to the free-surface forming a layer of uniform thickness. By comparison, the liquid in the A-site deficient composition segregates to the free-surface forming islands and leaving porous regions in the bulk matrix. It is concluded that the different liquid phase compositions in the A-site excess and A-site deficient (La,Ca)CrO3 have dissimilar wetting characteristics during the later stages of sintering. The A-site deficient liquid forms a premature solid phase, which accounts for the difference in sintering behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355140
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  • 8
    Electronic Resource
    Electronic Resource
    Oxygen activity dependence of the defect structure of La-doped BaTiO3 (1984)
    Springer
    Journal of materials science 19 (1984), S. 3159-3165 
    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 A model for the behaviour of donor-doped BaTiO3 as a function of oxygen activity is proposed. Thermogravimetric measurements show good agreement with the proposed model. The results show that donor-doped BaTiO3 is stoichiometric with electronic compensation of the donor at low oxygen activity, but with increasing oxygen activity, compensation becomes ionic as excess oxygen is absorbed. The possible compensation mechanisms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00549799
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  • 9
    Electronic Resource
    Electronic Resource
    Oxidation-reduction behaviour of La-doped SrTiO3 (1984)
    Springer
    Journal of materials science 19 (1984), S. 2593-2598 
    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 Thermogravimetric measurements as a function of oxygen activity were performed in the temperature range of 1200 to 1400° C on a series of lanthanum SrTiO3 compounds. A model which assumes the absorption of excess oxygen in the structure which compensates the donors by formation of cationic defects is postulated. Comparison of this model with the experimental results show reasonable agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550814
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of cation substitution on the thermal expansion coefficient of LaCrO3 (1992)
    Springer
    Journal of materials science 11 (1992), S. 1191-1192 
    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/10.1007/BF00730282
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