Edward E. Abbott

Enhancement of the power factor of the transition metal pentatelluride HfTe5 by rare-earth doping

The transition metal pentatellurides HfTe5 and ZrTe5 have been observed to possess interesting electrical transport properties with high thermopower and low resistivity values leading to high thermoelectric power factors. We have investigated the effect of doping HfTe5 with rare-earth elements by measuring the power factor data from about 10K to room temperature on single crystals of Hf1−xRxTe5, where R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, and Ho. Samples that have been doped with Nd (Hf1−xNdxTe5) possess power factors more than a factor of 2 larger than that of the commonly used thermoelectric material Bi2Te3.

Thermoelectric properties of doped titanium disulfides

We report herein the doping of titanium disulfide (TiS2) with the pnictides (Pn): P, As, and Sb. The incorporation of these pnictides into titanium disulfide (TiS2−xPnx) is performed at extremely low concentrations (x∼0.2%). The effects on the electronic transport of titanium disulfide by doping with arsenic is quite profound, reducing the resistivity and thermopower to 0.2mΩcm and −35μV∕K at 300K, respectively, from 1.8mΩcm and −170μV∕K at 300K for the parent compound TiS2. For a wide range of thermopower values we find that the thermopower (α) of these doped titanium disulfides is linearly related to the infrared reflectivity minimum and can be correlated by the experimentally determined proportionality of λ=−0.0457α, where λ is the wavelength of the minimum.

Thermoelectric Properties of TiS 2 type materials

TiS 2 belongs to a family of layered compounds that displays promise as a thermoelectric material. At room temperature the thermopower (a) of TiS 2 displays an n-type behavior, with a magnitude of ≈ -200 μV/K. The electrical resistivity (ρ), is on the order of 1 mΩ-cm at room temperature and displays a “metallic-like” behavior with dR/dT > 0 from 300 K to 10 K. Thus, these compounds exhibit relatively large power factors (PF = α 2 /ρ) with a PF ∼30 μW/K 2 cm at T = 300 K, which are comparable to the state-of-the art Bi 2 Te 3 type materials, which have a PF ∼40 μW/K 2 , at T = 330K. These values suggest that further investigations of these systems could be profitable. Thin plate-like crystals of TiS 2 are grown by the iodine vapor transport method with planar dimensions of 1 cm and thicknesses of 20 μm or more. In this synthetic approach some dopants can be integrated into the parent compound, effectively providing a route for the tuning of electronic properties. We present here some effects of elemental doping on the electronic properties in these TiS 2 based materials.

Effect of rare earth doping on the thermoelectric and electrical transport properties of the transition metal pentatelluride HfTe/sub 5/

The transition metal pentatellurides HfTe/sub 5/ and ZrTe/sub 5/ have been observed to possess high thermoelectric power factors and anomalous electrical transport behavior. The temperature dependence of the resistivity is semimetallic except for a large resistive peak as a function of temperature at around 75 K for HfTe/sub 5/ and 145 K for ZrTe/sub 5/. At a temperature corresponding to this peak, the thermopower crosses zero as it moves from large positive values to large negative values. Previous doping studies have shown profound and varied effects on the anomalous transport. In this study we investigate the effect on the electrical resistivity, thermopower, and magnetoresistance of doping HfTe/sub 5/ with rare-earth elements. Doping with rare-earth elements of increasing atomic number leads to a systematic suppression of the anomalous transport behavior and large magnetoresistive effect observed in the parent compound. Rare-earth doping also leads to an enhancement of the thermoelectric power factor over previously studied pentatellurides. For nominal Hf/sub 0.75/Nd/sub 0.25/Te/sub 5/ and Hf/sub 0.75/Sm/sub 0.25/Te/sub 5/, values more than a factor of 2 larger than that of the commonly used thermoelectric material Bi/sub 2/Te/sub 3/ were observed.