Japheth F. Rauscher

University of California, Davis, Davis, California, United States

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Publications (8)16.4 Total impact

  • Catherine A. Uvarov · Japheth F. Rauscher · Susan M. Kauzlarich
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    ABSTRACT: The properties of the isovalent substitution of Ca2+ for Yb2+ will be presented for the Yb14-xCaxMnSb11 solid solution made by a direct reaction of elements (x = 0, 1, 2, 3, 4) with excess Mn (2x). Composition and phase purity was analyzed via powder X-ray diffraction. Electron microprobe analysis showed the presence of Mn inclusions. High temperature thermoelectric property measurements were performed including Seebeck, resistivity, and thermal conductivity (300 1300 K). While all the samples had impurities present, the Seebeck coefficients were enhanced, electrical resistivity was higher and showed a peak at approximately 800 K which may be attributed to Mn inclusions. The total thermal conductivity was lowered compared with Yb14Sb11, as expected for replacing the heavier Yb2+ with the lighter Ca2+ cation. The maximum zT for the Yb14-xCaxMnSb11 system was observed for x = 2, reaching the value of 1 at 1200 K.
    Science of Advanced Materials 08/2011; 3(4):646-651. DOI:10.1166/sam.2011.1195 · 2.91 Impact Factor
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    ABSTRACT: The Zintl phase Yb(14)MnSb(11) was successfully doped with Ge utilizing a tin flux technique. The stoichiometry was determined by microprobe analysis to be Yb(13.99(14))Mn(1.05(5))Sb(10.89(16))Ge(0.06(3)). This was the maximum amount of Ge that could be incorporated into the structure via flux synthesis regardless of the amount included in the reaction. Single crystal X-ray diffraction could not unambiguously determine the site occupancy for Ge. Bond lengths varied by about 1% or less, compared with the undoped structure, suggesting that the small amount of Ge dopant does not significantly perturb the structure. Differential scanning calorimetry/thermogravimetry (DSC/TG) show that the doped compound's melting point is greater than 1200 K. The electrical resistivity and magnetism are virtually unchanged from the parent material, suggesting that Yb is present as Yb(2+) and that the Ge dopant has little effect on the magnetic structure. At 900 K the resistivity and Seebeck coefficient decrease resulting in a zT of 0.45 at 1100 K, significantly lower than the undoped compound.
    Dalton Transactions 01/2010; 39(4):1055-62. DOI:10.1039/b920250a · 4.20 Impact Factor
  • ChemInform 01/2010; 41(1). DOI:10.1002/chin.201001004
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    ABSTRACT: Single crystals of the new Zintl phases AIn2P2 [A = Ca (calcium indium phosphide), Sr (strontium indium phosphide) and Ba (barium indium phosphide)] have been synthesized from a reactive indium flux. CaIn2P2 and SrIn2P2 are isostructural with EuIn2P2 and crystallize in the space group P63/mmc. The alkaline earth cations A are located at a site with 3m symmetry; In and P are located at sites with 3m symmetry. The structure type consists of layers of A2+ cations separated by [In2P2]2- anions that contain [In2P6] eclipsed ethane-like units that are further connected by shared P atoms. This yields a double layer of six-membered rings in which the In-In bonds are parallel to the c axis and to one another. BaIn2P2 crystallizes in a new structure type in the space group P2(1)/m with Z = 4, with all atoms residing on sites of mirror symmetry. The structure contains layers of Ba2+ cations separated by [In2P2]2- layers of staggered [In2P6] units that form a mixture of four-, five- and six-membered rings. As a consequence of this more complicated layered structure, both the steric and electronic requirements of the large Ba2+ cation are met.
    Acta Crystallographica Section C Crystal Structure Communications 10/2009; 65(Pt 10):i69-73. DOI:10.1107/S0108270109035987 · 0.54 Impact Factor
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    ABSTRACT: We investigated the effect of Cd and Sn doping on the superconducting (SC) transition temperature Tc, the superconducting critical field Hc2, and the High-Field-Low- Temperature (HFLT) phase in heavy fermion superconductor CeCoIn5. Tc decreases monotonically for both dopants, whereas Hc2 rises initially with Cd substitution, while dropping for Sn doping. Analysis of the magnetization data suggests that these effects are caused by weakening of the Pauli limiting in CeCoIn5 with Cd doping, most likely due to changes of susceptibility of the normal state. Both Cd (leading to AFM ground state at higher concentrations) and Sn impurities, at a very low level of a few hundred ppm, suppress the HFLT phase. We interpret these results as supporting the superconducting origin of the HFLT phase.
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    ABSTRACT: We studied the effect of impurity on the first order superconducting (SC) transition and the high field-low temperature (HFLT) SC state of CeCoIn5 by measuring the specific heat of CeCo(In1-xCdx)_{5} with x=0.0011, 0.0022, and 0.0033 and CeCo(In1-xHgx)_{5} with x=0.000 16, 0.000 32, and 0.000 48 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the crossover temperature T0, where the SC transition changes from second to first order, to T=0 K with x=0.0022 for H parallel[100], while it remains roughly constant up to x=0.0033 for H parallel[001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.000 48, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the nonmagnetic, possibly FFLO, origin of the HFLT state in CeCoIn5.
    Physical Review Letters 08/2008; 101(3):037001. DOI:10.1103/PhysRevLett.101.037001 · 7.51 Impact Factor
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    ABSTRACT: Zintl phase compounds with large unit cells and complex anionic structures such as Yb11Sb10 hold potential for being good thermoelectric materials. Single crystals of Ge-doped Yb11Sb10 were synthesized using a molten Sn-flux technique. Single crystal X-ray diffraction data were obtained and resulted in a composition of Yb11Sb9.3Ge0.5 which was verified by microprobe. Yb11Sb9.3Ge0.5 is isostructural to Ho11Ge10, crystallizing in a body-centered, tetragonal unit cell, space group I4/mmm, with Z = 4. The unit cell parameters of Yb11Sb9.3Ge0.5 are a = 11.8813(4), c = 17.1276(13) Å with a volume of 2417.8(2) Å3. These parameters correlate well with the structural refinement of previously published Yb11Sb10. The structure consists of 16 isolated Sb3− anions, 8 dumbbells, 2 square planar rings and 44 Yb2+ cations. The Ge, doped in at 28 % occupancy, was found to be site specific, residing on the 2 square planar rings. Single crystal X-ray diffraction is most consistent with the site that makes up the square ring being less than fully occupied. The doped compound is additionally characterized by X-ray powder diffraction, differential scanning calorimetry and thermogravimetry. High temperature (300–1200 K) thermoelectric properties show that the doped compound has extremely low thermal conductivity (10–30 mW/cmK), lower than that of Yb11Sb10. Temperature dependent resistivity is consistent with a heavily doped semiconductor. Yb11Sb9.3Ge0.5 shows p-type behavior increasing from ∼22 μV/K at room temperature to ∼31 μV/K at 1140 K. The low value and the temperature dependence of the Seebeck coefficient suggest that bipolar conduction produces a compensated Seebeck coefficient and consequently a low zT.
    Zeitschrift für anorganische und allgemeine Chemie 08/2007; 633(10):1587 - 1594. DOI:10.1002/zaac.200700267 · 1.25 Impact Factor