29 research outputs found
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
Z topology and superconductivity from symmetry lowering of a 3D Dirac Metal AuPb
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 AuPb 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 = -1 invariant in
the low temperature phase indicates that AuPb in its superconducting state
must have topological surface states. These characteristics make AuPb 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