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  • 1
    Electronic Resource
    Electronic Resource
    Thermophysical properties of the lanthanide sesquisulfides. I. Schottky functions and magnetic and electronic properties of γ-La2S3, γ-Ce2S3, γ-Nd2S3, and γ-Gd2S3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4838-4848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Heat capacity measurements of four lanthanide sesquisulfides La2S3, Ce2S3, Nd2S3, and Gd2S3, prepared in the γ phase, have been obtained between 6 and 350 K by adiabatic calorimetry. The total heat capacity has been resolved into lattice, electronic, magnetic, and Schottky components. The Schottky contributions agree well with the calculated values based on the observed splitting of the ground-state manifold of the rare earth ions occupying sites of S4 symmetry in the Th3P4 structure. The observed splitting is obtained from an analysis of the hot bands in the absorption spectrum and from direct observation of the Stark levels in the far infrared. The Stark levels (all doublets) for Ce2S3 (2F5/2) are 0, 185, and 358 cm−1; for Nd2S3(4I9/2), they are 0, 76, 150, 180, and 385 cm−1. For La2S3, which has no Schottky or magnetic contributions to the heat capacity, the thermal data can be extrapolated to 0 K. The entropy for La2S3 at 298.15 K (as S0/R) is 19.51. Schottky and magnetic ordering at lower temperatures in Ce2S3, Nd2S3, and Gd2S3 preclude such extrapolation techniques. Therefore the entropy at 298.15 K for these compounds {S0–S0(7 K)}/R, is 21.34, 22.38, and 20.05, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456722
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  • 2
    Electronic Resource
    Electronic Resource
    Thermophysical properties of the lanthanide sesquisulfides. II. Schottky contributions and magnetic and electronic properties of γ-phase Pr2S3, Tb2S3, and Dy2S3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1964-1972 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Heat-capacity measurements by adiabatic equilibrium calorimetry are reported for γ-phase Pr2S3, Tb2S3, and Dy2S3 between 5 and 350 K. Highly purified samples were prepared and their composition verified by chemical analysis. Precision lattice parameters were determined for each compound and are compared with literature values. The total heat capacity has been resolved into lattice, magnetic, and Schottky components by a volumetric approach. The experimental Schottky contributions accord with the calculated curves based on the crystal-field splitting of the 2S+1LJ ground state of the lanthanide ions occupying sites of S4 symmetry in the Th3P4 lattice. The individual crystal-field electronic energy levels have been obtained in part from an analysis of the hot-band data observed in the absorption spectra of Pr2S3, Tb2S3, and Dy2S3, and from a calculated splitting in which the crystal-field parameters Bkm, were determined from a lattice-sum calculation. Molar thermodynamic properties are reported for all three compounds. The entropy at 298.15 K {S0−S0 (7 K)}, is 22.78R, 22.93R, and 23.36R, for γ-phase Pr2S3, Tb2S3, and Dy2S3, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460993
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  • 3
    Electronic Resource
    Electronic Resource
    Parasitic effects of oxygen on the thermoelectric properties of Si80Ge20 doped with GaP and P (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1423-1428 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The presence of oxygen in silicon-germanium can have a significant effect on the sintering, microstructural, and transport properties of these alloys. A neutron activation study was performed to follow the total oxygen content during the preparation of mechanically alloyed n-type Si-20 at. % Ge alloys using either fine powders, polycrystalline Czochralski chunk, or single-crystal float zoned starting materials. The alloys were prepared with a nominal composition of Si0.747Ge0.187(GaP)0.016P0.034. The total oxygen concentration was measured in the starting materials, after 6 h of mechanical alloying in a helium environment, after hot pressing, and after a 3 h, 1100 °C heat treatment in fused silica ampoules. Alloys that contained oxygen levels in excess of 2.0 at. % exhibited low carrier mobility and low thermal conductivity, whereas those that contained less than 0.6 at. % oxygen possessed high mobility and thermal conductivity. The microstructure, as observed by optical metallography and scanning electron microscopy, was found to differ greatly with oxygen content as the low oxygen alloys showed relatively large, well-defined grains and the high oxygen alloys showed evidence of poor sintering and limited grain growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351702
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  • 4
    Electronic Resource
    Electronic Resource
    Pressure-assisted reaction bonding between W and Si80Ge20 alloy with Ni as the interlayer (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4292-4299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conditions and reaction mechanism of W/Ni/Si80Ge20 hot-press bonding have been studied. It was found that a Ni/Si80Ge20 bond can be formed using low pressure, 19.6 MPa, in the temperature range between 780 and 900 °C in a short time. The kinetics follows a parabolic pattern, suggesting it is a diffusion-controlled process. The activation energy is 2.7 eV and the parabolic rate constant is given by KP = 4.0 × 1014 exp(−3.2×104/T) (μm2/min). The bonding interface has a multilayered structure. A phenomenological mechanism of the bonding formation has been proposed based on scanning electron microscopy observations and energy dispersive spectroscopy. The cracking problem due to thermal stress is discussed based on Oxx's equation. It was found that bonds free from cracks in the Si80Ge20 alloy are formed when the Ni consumption (as measured by the thickness of the nickel layer) is sufficiently small (〈40–45 μm) and the post-hot-press cooling is slow. On the other hand, tungsten and nickel react during hot pressing at higher temperature, forming WNi4. As an interlayer, nickel can join the tungsten sheet and the Si80Ge20 together. It has been also demonstrated that a thin nickel layer formed by vapor deposition on a tungsten sheet may be used as the interlayer in place of nickel sheet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348402
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  • 5
    Electronic Resource
    Electronic Resource
    Pressure-assisted reaction bonding between a W sheet and a Si80Ge20 alloy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4846-4852 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conditions and mechanism of bonding a tungsten sheet directly onto a Si80Ge20 alloy by hot pressing have been studied. It was found that W/Si80Ge20 bonds are formed only at relatively high temperatures. The pressure and time required for bonding decrease with increasing temperature. In the initial stage, the W/Si80Ge20 reaction follows a parabolic kinetics, suggesting it is a diffusion-controlled process. The activation energy is 4.9 eV, and the parabolic rate constant is given by Kp=(4.2±0.1)×1018 exp[−(5.7±0.1)×104/T] (μm2/ min) A bonding mechanism is proposed based on scanning electron microscopic observations and chemical analyses of the interface. Selective reaction between silicon and tungsten leaves a Ge-rich layer at the W/Si80Ge20 interface, thus reducing the melting temperature. When the silicon content in the interfacial layer becomes sufficiently low, the layer melts at the hot-press temperature. Molten materials fill in voids and microcracks by the capillary effect, resulting in an intimate contact and a strong bond. A mathematical model of Si diffusion is proposed. Solving the equation by the finite-difference method, silicon composition profiles were obtained and the silicon diffusion coefficient was estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346144
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  • 6
    Electronic Resource
    Electronic Resource
    Thermophysical properties of the lanthanide sesquisulfides. III. Determination of Schottky and lattice heat-capacity contributions of γ-phase Sm2S3 and evaluation of the thermophysical properties of the γ-phase Ln2S3 subset (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6149-6156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the experimental heat capacity of γ-phase Sm2S3 and derived thermophysical properties at selected temperatures. The entropy, enthalpy increments, and Gibbs energy function are 21.50R, 3063R⋅K, and 11.23R at 298.15 K. The experimental heat capacity is made up of lattice and electronic (Schottky) contributions. The lattice contribution is determined for all γ-phase lanthanide sesquisulfides (Ln2S3 ) using the Komada/Westrum model. The difference between the experimental heat capacity and the deduced lattice heat capacity is analyzed as the Schottky contribution. Comparisons are made between the calorimetric Schottky contributions and those determined based on crystal-field electronic energy levels of Ln3+ ions in the lattice and between the Schottky contributions obtained from the empirical volumetric priority approach and from the Komada/Westrum theoretical approach. Predictions for the thermophysical properties of γ-phase Eu2S3 and γ-phase Pm2S3 (unavailable for experimental determination) are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462857
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  • 7
    Electronic Resource
    Electronic Resource
    Erratum: "High-temperature thermodynamic properties of alpha and gamma lanthanum sesquisulfides and related compounds'' [J. Appl. Phys. 59, 3437 (1986)] (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3384-3384 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337713
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation of γ-LaSy (1.33〈y〈1.50) alloys by the pressure-assisted reaction sintering method and their thermoelectric properties (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4633-4637 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pressure-assisted reaction sintering (PARS) method was used to prepare thermoelectric elements of the γ-phase lanthanum sesquisulfide solid solution alloys which exist over a wide homogeneity range: LaSy (1.33〈y〈1.5). A mixture of powders of stoichiometric lanthanum sesquisulfide (La2S3) and lanthanum trihydride (LaH3) was reaction sintered in a hot-press to make the desired composition of γ-LaSy. This method produced black dense single-phase γ-LaSy pellets with a theoretical density of 97% or better. The thermoelectric properties (electrical resistivity and Seebeck coefficient) of the samples prepared by the PARS technique were measured. The room temperature electrical resistivity and Seebeck coefficient of γ-LaSy varied in a systematic manner with the electron concentration indicating that γ-LaSy alloys behave like a simple metal. Although the current carriers appear to be quite heavy (drift mobility ∼3 cm2/V s), the temperature dependence (up to 1000 °C) of these properties of LaS1.42 were found to be linear functions, which is in accord with the above observations. The thermoelectric figure of merit based on the measured resistivity and Seebeck coefficient and an estimated thermal conductivity for LaS1.42 is 0.75×10−3 °C−1 at 1000 °C, which is comparable to those of the state-of-the-art materials such as silicon–germanium alloys at 1000 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335373
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of small amounts of hydrogen on the elastic behavior of lutetium (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1220-1223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The elastic constants of a well-characterized, high-purity single crystal were measured before and after hydrogen was added to change the hydrogen content from 500 at. ppm (3 wt. ppm) to 6900 at. ppm (40 wt. ppm). Comparison between the two sets of measurements shows that such a small change in hydrogen content has a disproportionately large effect on the elastic stiffness. In this case the increase in hydrogen content produced an increase in all directly measured elastic constants by the order of 0.5%. Further comparison of our data with earlier data indicates that other interstitial elements (e.g., C, N, and O) may also exert an inordinately large influence on the elastic stiffness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339856
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  • 10
    Electronic Resource
    Electronic Resource
    High-temperature thermodynamic properties of alpha and gamma lanthanum sesquisulfides and related compounds (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 3437-3440 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high-temperature heat contents of La2S3(α), La2S3(γ), La3S4, and La2.65Eu0.35S4 were measured from 400 to 1800 K by using a copper block drop calorimeter. The heat and entropy of transition of the α-to-γ transformation of La2S3 was determined. Equations for the thermodynamic functions H0T−H0298.15, Cp, S0T−S0298.15 and −(F0T−H0298.15)/T were derived in terms of the least-squares fit parameters of the heat content data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336811
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