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  • 1
    Electronic Resource
    Electronic Resource
    Electronic structure of CMR manganites (invited) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5330-5335 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A "colossal" negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition. The Mn4+ and high-spin Mn3+ ions each contain localized t3 configurations; the t3–pπ–t3 superexchange interactions are antiferromagnetic. The orbital degeneracy of localized Mn3+:t3e1, 5Eg configurations is lifted by cooperative static or dynamic Jahn–Teller deformations. Strong e-electron coupling to oxygen displacements, static or dynamic, introduces ferromagnetic e1–pσ–e0 interactions either via superexchange or, for fast Mn3+ to Mn4+ electron transfer relative to the spin-relaxation time (τh〈τs), via a stronger double exchange. At the first-order ferromagnetic transition, a change from τh(approximate)(h-dash-bar)/Wσ〉ωR−1 to τh〈ωR−1 occurs within mobile molecular units, where Wσ is the bandwidth for states of e-orbital parentage and ωR−1 is the period of the optical-mode lattice vibration that traps a mobile hole as a small-polaron Mn4+ ion. TC increases with the fraction of double-exchange couplings, and this fraction increases with Wσ and ωR at the transition from polaronic to itinerant-electron behavior below TC. The bandwidth Wσ∼εσλσ2 cos φ〈cos(θij/2)〉 depends on the covalent mixing parameter λσ, which increases with pressure, as well as on the Mn–O–Mn bond angle (180°−φ), which increases with the tolerance factor t that measures the equilibrium bond-length mismatch, and on the angle θij between neighboring spins so that Wσ increases with the spontaneous magnetization on cooling below TC. In the compositions Ln0.7A0.3MnO3 with A=Ca or Sr, TC increases with t over the range 0.96≤t≤0.98 where the transition at TC is first order. The CMR is greatest near t(approximate)0.96; it reflects a trapping out of mobile holes with decreasing temperature in the paramagnetic phase and their progressive release with decreasing temperature in the ferromagnetic phase where spin entropy is exchanged for configurational entropy. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364536
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  • 2
    Electronic Resource
    Electronic Resource
    Surface protonation and electrochemical activity of oxides in aqueous solution (1990)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 112 (1990), S. 2076-2082 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00162a006
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  • 3
    Electronic Resource
    Electronic Resource
    Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6761-6763 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited or LaAlO3 and SrTiO3 (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr2FeMoO6 was obtained in 100 mTorr 99.999% Ar gas at 825 °C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization Ms at 10 K of 3.2μB/f.u. However, the Curie temperature TC(approximate)380 K was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers Ms at 300 K in the thin films to 1.5μB/f.u. compared to 2.2μB/f.u. in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372833
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  • 4
    Electronic Resource
    Electronic Resource
    Intraalloy electron transfer and catalyst performance: a spectroscopic and electrochemical study (1989)
    s.l. : American Chemical Society
    Chemistry of materials 1 (1989), S. 391-398 
    Details
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cm00004a003
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  • 5
    Electronic Resource
    Electronic Resource
    Intra- versus intergranular low-field magnetoresistance of Sr2FeMoO6 thin films (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2812-2814 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited on LaAlO3 and SrTiO3 (001) substrates. Comparison of their transport and magnetic properties with those of polycrystalline ceramic samples shows a metallic versus semiconductor temperature dependence and a saturation magnetization Ms at 10 K of 3.2 μB/f.u. in the film as against 3.0 for a tetragonal polycrystalline sample. However, the Curie temperature TC(approximate)389 K is reduced from 415 K found for the tetragonal ceramic, which lowers Ms at 300 K in the thin films to 2.0 μB/f.u. compared to 2.2 μB/f.u. in the ceramics. A Wheatstone bridge arrangement straddling a bicrystal boundary has been used to verify that spin-dependent electron transfer through a grain boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125158
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  • 6
    Electronic Resource
    Electronic Resource
    Superior Perovskite Oxide-Ion Conductor; Strontium- and Magnesium-Doped LaGaO3: I, Phase Relationships and Electrical Properties (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), 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 single-phase, cubic-perovskite region of the LaO1.5-SrO-Gao1.5-MgO phase diagram was determined from room-temperature and high-temperature X-ray diffraction. Two impurity phases were identified, LaSrGaO4 and aSrGa3O7. The conductivity of the oxygen-deficient perovskite phase was shown to be essentially a purely oxide-ion conductivity sigmao over a wide range of oxygen partial pressures 10-22 lessthan equal to PO2 lessthan equal to 1 atm. The highest values of sigmao = 0.17 and 0.08 S/cm were found for La0.8Sr0.2Ga0.83Mg0.17O0.2815 at 800° and 700°C, respectively; they remain stable over a week-long test. The Arrhenius plot of sigmao is curved, dividing into a high-temperature region T 〉 T* similar/congruent 600°C and a low-temperature region T 〈 T*. Above T* all the oxygen vacancies appear to be mobile; below T* they progressively condense into clusters of ordered vacancies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02662.x
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis and Electrical Properties of Dense Ce0.9Gd0.1O1.95 Ceramics (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), 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: Uniform spherical powders of Ce0.9Gd0.1O1.95 with an average diameter of 250 nm were obtained at 700°C from a sol-gel process of mixing nitrates and ethylene glycol. Broadening of the X-ray peaks of the fluorite structure reveals a small crystallite size within the powders. Sintering in air of pressed pellets of the powders at 1585°C gives ceramics of 99% theoretical density with grain sizes 1-10 µm and a cubic unit cell a= 5.422 ± 0.034 Å. The electrical conductivity σ=σo+σe has two components. In air or argon, the electronic component σe is negligible and the oxide-ion conductivity σo is not described by a classical Arrhenius equation; a pronounced curvature at T similar/congruent T* has been observed in the Arrhenius plot of the bulk conductivity. The system could be modeled by a condensation of mobile oxygen vacancies into ordered clusters below a temperature T* similar/congruent 583 ± 45°C and a motional enthalpy ΔHm= 0.63 ± 0.01 eV for the vacancies. A measured trapping energy ΔHt(1 - T/T*) has ΔHt= 0.19 ± 0.01 eV = 2.57 kT*. In a reducing atmosphere, σe exhibits a small-polaron motional enthalpy ΔHp= 0.40 ± 0.08 eV for transfer of a 4 f electron from a Ce3+ to a Ce4+ ion and a ΔHp+ΔHpt= 0.51 ± 0.04 eV at T 〈 T*.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02341.x
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  • 8
    Electronic Resource
    Electronic Resource
    Superior Perovskite Oxide-Ion Conductor; Strontium- and Magnesium-Doped LaGaO3: III, Performance Tests of Single Ceramic Fuel Cells (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), 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 performance of La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) as an optimized electrolyte of a solid oxide fuel cell was tested on single cells having a 500-µm-thick electrolyte membrane. The reactivity of NiO and LSGM suggested use of an interlayer to prevent formation of LaNiO3. The interlayer Sm-CeO2 was selected and sandwiched between the electrolyte and anode. Comparison of Sm-CeO2/Sm-CeO2+ Ni and Sm-CeO2+ Ni as anodes showed that Sm-CeO2/Sm-CeO2+ Ni gave an exchange current density 4 times higher than that of Sm-CeO2+ Ni. The peak power density of the interlayered cell is 100 mW higher than that of the standard cell without the interlayer. This improvement is due to a significant reduction of the anode overpotential; the overpotential of the cathode La0.6Sr0.4CoO3-delta (LSCo) remained unchanged. Comparison of the peak power density in this study and with that of a previous study, also with a 500-µm-thick electrolyte, indicates a factor of 2 improvement, i.e., from 270 mW/cm2 to 550 mW/cm2 at 800°C. The excellent cell performance showed that an LSGM-based thick membrane SOFC operating at temperatures 600° 〈 Top 〈 800°C is a realistic goal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02664.x
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  • 9
    Electronic Resource
    Electronic Resource
    Superior Perovskite Oxide-Ion Conductor; Strontium- and Magnesium-Doped LaGaO3: II, ac Impedance Spectroscopy (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), 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: Alternating current impedance spectroscopy and electron microscopy were used to investigate the effect of grain boundaries in LSGM-based materials. The impurity LaSrGa3O7 existing in the samples La0.8Sr0.2Ga1-yMgy-O3–0.5(0.2+y) (y= 0.05–0.10) gives a contribution to a perfect or depressed grain-boundary semicircle in the impedance spectroscopy. The depressed semicircle represents a constant phase element (CPE) indicating LaSrGa3O7 is an oxide-ion insulator. The grain-boundary semicircle vanishes if a hydrogen-containing atmosphere is applied. This fact may reflect proton conduction in LaSrGa3O7. In contrast, the impurity LaSrGaO4 existing, for example, in the samples x= 0.20, y= 0.25–0.30 gives no grain-boundary contribution to the impedance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02663.x
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  • 10
    Electronic Resource
    Electronic Resource
    OXIDE-ION ELECTROLYTES (2003)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 33 (2003), S. 91-128 
    Details
    ISSN: 1531-7331
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The performance of the oxide-ion electrolyte of a solid oxide fuel cell (SOFC) is critical to the development of an intermediate-temperature system. Although yttria-stabilized zirconia is the electrolyte used in SOFCs under commercial development, other candidate materials are now available, and there remains a strong motivation to search for new, improved oxide-ion electrolytes. The leading contenders are discussed not only with respect to their oxide-ion conductivity, but also with respect to mechanical and chemical compatibility with the electrodes and the working environment at each electrode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.matsci.33.022802.091651
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