Growth of FeSb2 thin films by magnetron sputtering

The detailed growth of FeSb₂ films formed on quartz (0001) substrates by magnetron sputtering is reported. FeSb₂ films with different orientations and compositions can be produced by adjusting the Ar working gas pressure and the substrate temperature. By employing FeSb₂ thin layers produced at different substrate temperatures as templates, < 101>-, < 120>- and < 002>-textured FeSb₂ films were produced under identical growth conditions. The thermoelectric properties of film samples grown at different temperatures were measured and the effects of Sb and FeSb impurities were investigated.     

Suppression of bipolar transport and enhanced zT values of porous ZnSb by addition of hydrothermally synthesized Sb

ZnSb is a favourable eco-friendly, earth abundant SIand low cost thermoelectric material. We herein report a feasible approach to improve the thermoelectric performance of ZnSb by compositing with hydrothermally synthesized Sb. A series of ZnSb/Sb composites was fabricated by mixing the host material ZnSb and hydrothermally synthesized Sb followed by consolidation using cold pressing and evacuating-and-encapsulating sintering at 530 °C for 3 h. As compared to the host ZnSb, both the electrical resistivity and thermopower decrease, while both the power factor and thermal conductivity increase upon compositing with Sb. The bipolar transport of ZnSb is suppressed at temperatures up to 600 K. As a result, the ZnSb-Sb composite with 4 wt.% of hydrothermally synthesized Sb has a zT = 1.18 at 600 K, which is one of the highest values for ZnSb-based material and is about 46% enhancement as compared to the host ZnSb having zT = 0.81 at 600 K.     

Studies of thermoelectric transport properties of atomic layer deposited gallium-doped ZnO

The thermoelectric transport properties of atomic layer deposited (ALD) gallium doped zinc oxide (GZO) thin films were investigated to identify their potential as a thermoelectric material. The overall thermoelectric properties, such as the Seebeck coefficient and electrical conductivity, were probed as a function of Ga concentration in ZnO. The doping concentration was tuned by varying the ALD cycle ratio of zinc oxide and gallium oxide. The GZO was deposited at 250 °C and the doping concentration was modified from 1% to 10%. Sufficient thermoelectric properties appeared at a doping concentration of 1%. The crystallinity and electronic state, such as the effective mass, were investigated to determine the enhancement of the thermoelectric properties. The efficient Ga doping of GZO showed a Seebeck coefficient of 60 μV/K and an electrical conductivity of 1808.32 S/cm, with a maximum power factor of 0.66 mW/mK².     

Effect of compositional dependence on physicochemical properties of Bi2Se3 doped system

Crystalline bulk compositions of Bi₂ (Se_1−xTe_x)₃ system with ( x=0.0–1.00) were prepared using the conventional melting method. The structural properties of bulk samples were studied with the aid of XRD and SEM analysis. Compositional element distribution and elemental ratios were estimated with EDX spectroscopy that attached with SEM. XRD patterns show that the prepared compounds are crystalline materials with single phases of Bi₂Se₃ and Bi₂Te₃ and/or a ternary phase. The grain size calculations were performed using the well-known Scherrer equation. The thermal studies analysis was carried out by using DSC. DSC studies revealed that the prepared samples are stable and none decomposable over the temperature range. Physicochemical properties such as compactness, molar volume and the free volume percentage were calculated for the concerned alloys based on the experimentally calculated densities of each compound. The measured parameters showed a strong dependence on the Te content.     

Electronic structure and thermoelectric properties of the thioantimonate FePb4Sb6S14

The title compound was synthesized and its thermoelectric properties investigated. Electronic structure calculations and electrical conductivity measurements show semiconducting behavior. The results of thermopower measurements are presented. The high thermopower motivated us to investigate the effects arising from chemical doping. Cobalt and tin doped variants were synthesized and their physical property measurements show improved electrical conductivity.     

Thermal Expansion Studies of Selected High-Temperature Thermoelectric Materials

Radioisotope thermoelectric generators (RTGs) generate electrical power by converting the heat released from the nuclear decay of radioactive isotopes (typically plutonium-238) into electricity using a thermoelectric converter. RTGs have been successfully used to power a number of space missions and have demonstrated their reliability over an extended period of time (tens of years) and are compact, rugged, radiation resistant, scalable, and produce no noise, vibration or torque during operation. System conversion efficiency for state-of-practice RTGs is about 6% and specific power ≤5.1 W/kg. A higher specific power would result in more onboard power for the same RTG mass, or less RTG mass for the same onboard power. The Jet Propulsion Laboratory has been leading, under the advanced thermoelectric converter (ATEC) project, the development of new high-temperature thermoelectric materials and components for integration into advanced, more efficient RTGs. Thermoelectric materials investigated to date include skutterudites, the Yb₁₄MnSb₁₁ compound, and SiGe alloys. The development of long-lived thermoelectric couples based on some of these materials has been initiated and is assisted by a thermomechanical stress analysis to ensure that all stresses under both fabrication and operation conditions will be within yield limits for those materials. Several physical parameters are needed as input to this analysis. Among those parameters, the coefficient of thermal expansion (CTE) is critically important. Thermal expansion coefficient measurements of several thermoelectric materials under consideration for ATEC are described in this paper. The stress response at the interfaces in material stacks subjected to changes in temperature is discussed, drawing on work from the literature and project-specific tools developed here. The degree of CTE mismatch and the associated effect on the formation of stress is highlighted.     

A study of the synthesis of bismuth tellurium selenide nanocompounds and procedures for improving their thermoelectric performance

A bismuth tellurium selenide (Bi₂Te_ySe_3−y) nanocompound for thermoelectric applications was successfully prepared via a water-based chemical reaction in an atmospheric environment. The compound was less that ca. 100 nm in size, with a crystalline structure corresponding to the rhombohedral Bi₂Te_2.7Se_0.3. We sintered the compound via a spark plasma sintering process under the designated sintering conditions and measured the transport properties (i.e., thermal conductivity, resistivity, Seebeck coefficient). The resulting specimens consisted of nanosized grains exhibiting a remarkably low thermal conductivity. Subsequently, we endeavored to improve the other transport properties by adjusting the carrier density of the compound and derived the overall thermoelectric performance by the figure of merit (ZT).     

Thermal transport in individual thermoelectric nanowires: a review

Abstract

Extensive research efforts have been devoted to nanowires because of their novel electronic, optical and thermoelectric properties due to spatial confinement in two dimensions. Among various fields, nanowires have been of interest in the thermoelectric community not only for their novel thermoelectric properties but also for their ease of use in fundamental scientific studies as the physics learned using nanowires can be applied in bulk thermoelectric nanocomposites. In this paper, we limit our discussion to experimental thermal transport in thermoelectric nanowires such as Bi–Te, Pb–Te and Si–Ge nanowires. After reviewing the reasons why nanowires are of interest in the thermoelectric community, we discuss various synthesis methods and thermal transport measurements. Next, we evaluated how thermal transport in nanowires is affected by various scattering mechanisms such as phonon boundary scattering, alloy scattering, etc. We also discuss a recent study concerning how the surface roughness affects phonon transport. This article is useful to gain insight into how to manage thermal transport in various applications.     

Thermoelectric Transport in a ZrN/ScN Superlattice

Metal/semiconductor superlattices have the potential for a high thermoelectric figure of merit. The thermopower of these structures can be enhanced by controlling the barrier height using high-energy electron filtering. In addition, phonon scattering at interfaces can reduce the lattice contribution to the thermal conductivity. In this paper, we present theoretical and experimental studies of the thermoelectric transport in ZrN/ScN metal/semiconductor superlattices. Preliminary measurement results show an exponential increase in the cross-plane electrical conductivity with increasing temperature, which indicates the presence of the barrier. Fit of the Boltzmann transport-based model with the data indicates a barrier height of 280 meV. The cross-plane Seebeck coefficient of the sample is also measured by combining Seebeck voltage transient measurements with the thermal imaging technique. A Seebeck coefficient of 820 μV/K at room temperature is extracted, which is in good agreement with the simulation result of 800 μV/K. Theoretical calculations predict that the ZrN/ScN structure can exhibit a ZT of 1.5 at 1300 K assuming lateral momentum is conserved and that a ZT of 3 is achievable if the lateral momentum is not conserved.