Thermoelectric Properties of Intermetallic Semiconducting RuIn3 and Metallic IrIn3

Low temperature (<400 K) thermoelectric properties of semiconducting RuIn3 and metallic IrIn3 are reported. RuIn3 is a narrow band gap semiconductor with a large n-type Seebeck coefficient at room temperature (S(290K)~400 {\mu}V/K), but the thermoelectric Figure of merit (ZT(290K) = 0.007) is small because of high electrical resistivity and thermal conductivity ({\kappa}(290 K) ~ 2.0 W/m K). IrIn3 is a metal with low thermopower at room temperature (S(290K)~20 {\mu}V/K) . Iridium substitution on the ruthenium site has a dramatic effect on transport properties, which leads to a large improvement in the power factor and corresponding Figure of merit (ZT(380 K) = 0.053), improving the efficiency of the material by an over of magnitude.Comment: Submitted to JA

Z2_2 topology and superconductivity from symmetry lowering of a 3D Dirac Metal Au2_2Pb

3D Dirac semi-metals (DSMs) are materials that have massless Dirac electrons and exhibit exotic physical properties It has been suggested that structurally distorting a DSM can create a Topological Insulator (TI), but this has not yet been experimentally verified. Furthermore, quasiparticle excitations known as Majorana Fermions have been theoretically proposed to exist in materials that exhibit superconductivity and topological surface states. Here we show that the cubic Laves phase Au$_2$Pb has a bulk Dirac cone above 100 K that gaps out upon cooling at a structural phase transition to create a topologically non trivial phase that superconducts below 1.2 K. The nontrivial Z$_2$ = -1 invariant in the low temperature phase indicates that Au$_2$Pb in its superconducting state must have topological surface states. These characteristics make Au$_2$Pb a unique platform for studying the transition between bulk Dirac electrons and topological surface states as well as studying the interaction of superconductivity with topological surface states

Effect of Chemical Doping on the Thermoelectric Properties of FeGa3

Thermoelectric properties of the chemically-doped intermetallic narrow-band semiconductor FeGa3 are reported. The parent compound shows semiconductor-like behavior with a small band gap (Eg = 0.2 eV), a carrier density of ~ 10(18) cm-3 and, a large n-type Seebeck coefficient (S ~ -400 \mu V/K) at room temperature. Hall effect measurements indicate that chemical doping significantly increases the carrier density, resulting in a metallic state, while the Seebeck coefficient still remains fairly large (~ -150 \mu V/K). The largest power factor (S2/{\rho} = 62 \mu W/m K2) and corresponding figure of merit (ZT = 0.013) at 390 K were observed for Fe0.99Co0.01(Ga0.997Ge0.003)3.Comment: 5 pages, 4 figures, To be appear in Journal of Applied Physic

Physical properties of the non-centrosymmetric superconductor Nb0.18Re0.82

We report the synthesis and measurements of magnetic, transport, and thermal properties of polycrystalline Nb0.18Re0.82, which has a superconducting transition at Tc ~ 8.8 K. The non-centrosymmetric alpha-Mn structure of the compound is confirmed by X-ray diffraction. Using the measured values for the lower critical field Hc1, upper critical field Hc2, and the specific heat C, we estimate the thermodynamic critical field Hc(0), coherence length {\xi}(0), penetration depth {\lambda}(0), and the Ginzburg-Landau parameter {\kappa}(0). The specific heat jump at Tc, {\Delta}C/{\gamma}Tc = 1.86, suggests that Nb0.18Re0.82 is moderately coupled superconductor. Below Tc the electronic specific heat decays exponentially, suggesting that the gap is isotropic. Our data suggests that the triplet admixture is weak in the polycrystalline form of compound. However, the estimated value of the upper critical field Hc2(0) is close to the calculated Pauli limit indicating the need for single crystal measurements.Comment: 15 pages, 8 figures, submitted to Physical Review

A novel experimental device for seebeck coefficient measurements of bulk materials, thin films, and nanowire composites

An experimental setup has been designed and built for measuring the Seebeck coefficient of bulk thermoelectric materials, thin films, and nanowire composites in the temperature range 200-350 K. The setup utilizes a differential method for measuring the Seebeck coefficient of the sample. The sample holder is a simple clamp design, utilizing a springloaded mounting system to load and hold the sample between two copper blocks, on which the electrical leads, as well as thermocouples, are mounted. The spring-loaded design also offers fast turn-around times, as the samples can be quickly loaded and unloaded. To measure the Seebeck coefficient, a temperature difference is generated across the sample by using four 10 kω resistive heaters mounted in series on one of the copper blocks. The resulting slope of the thermo-emf versus temperature difference plot is used to obtain the Seebeck coefficient at any temperature. Test measurements were carried out on bulk samples of nickel (Ni), bismuth-telluride (Bi2Te3), antimony-telluride (Sb2Te3), as well as thin films and nanowire composites of Ni. © 2011 by ASME