Search results for "thermoelectric material"
showing 10 items of 72 documents
On the Phase Separation in n-Type Thermoelectric Half-Heusler Materials
2018
Half-Heusler compounds have been in focus as potential materials for thermoelectric energy conversion in the mid-temperature range, e.g., as in automotive or industrial waste heat recovery, for more than ten years now. Because of their mechanical and thermal stability, these compounds are advantageous for common thermoelectric materials such as Bi 2 Te 3 , SiGe, clathrates or filled skutterudites. A further advantage lies in the tunability of Heusler compounds, allowing one to avoid expensive and toxic elements. Half-Heusler compounds usually exhibit a high electrical conductivity σ , resulting in high power factors. The main drawback of half-Heusler compounds is their high lattice th…
Segmented Thermoelectric Oxide-Based Module for High-Temperature Waste Heat Harvesting
2015
We report a high-performance thermoelectric (TE) oxide-based module using the segmentation of half-Heusler Ti_(0.3)Zr_(0.35)Hf_(0.35)CoSb_(0.8)Sn_(0.2) and misfit-layered cobaltite Ca_3Co_4O_(9+δ) as the p-leg and 2 % Al-doped ZnO as the n-leg. The maximum output power of a 4-couple segmented module at ΔT=700 K attains a value of approximately 6.5 kW m^(−2), which is three times higher than that of the best reported non-segmented oxide module. The TE properties of individual legs, as well as the interfacial contact resistances, were characterized as a function of temperature. Numerical modeling was used to predict the efficiency and to evaluate the influence of the electrical and thermal lo…
Rapid Microwave Preparation of Thermoelectric TiNiSn and TiCoSb Half-Heusler Compounds
2012
The 18-electron ternary intermetallic systems TiNiSn and TiCoSb are promising for applications as high-temperature thermoelectrics and comprise earth-abundant, and relatively nontoxic elements. Heusler and half-Heusler compounds are usually prepared by conventional solid state methods involving arc-melting and annealing at high temperatures for an extended period of time. Here, we report an energy-saving preparation route using a domestic microwave oven, reducing the reaction time significantly from more than a week to one minute. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds. The initia…
Enhanced thermoelectric properties of lightly Nb doped SrTiO3 thin films
2021
Novel thermoelectric materials developed for operation at room temperature must have similar or better performance along with being as ecofriendly as those commercially used, e.g., BiTe, in terms of their toxicity and cost. In this work, we present an in-depth study of the thermoelectric properties of epitaxial Nb-doped strontium titanate (SrTiNbO) thin films as a function of (i) doping concentration, (ii) film thickness and (iii) substrate type. The excellent crystal quality was confirmed by high resolution transmission electron microscopy and X-ray diffraction analysis. The thermoelectric properties were measured by the three-omega method (thermal conductivity) and van der Pauw method (el…
Electronic transport properties of electron- and hole-doped semiconductingC1bHeusler compounds:NiTi1−xMxSn(M=Sc,V)
2010
The substitutional series of Heusler compounds ${\text{NiTi}}_{1\ensuremath{-}x}{M}_{x}\text{Sn}$ (where $M=\text{Sc},\text{V}$ and $0lx\ensuremath{\le}0.2$) were synthesized and investigated with respect to their electronic structure and transport properties. The results show the possibility to create $n$-type and $p$-type thermoelectrics within one Heusler compound. The electronic structure and transport properties were calculated by all-electron ab initio methods and compared to the measurements. Hard x-ray photoelectron spectroscopy was carried out and the results are compared to the calculated electronic structure. Pure NiTiSn exhibits massive ``in gap'' states containing about 0.1 ele…
Tuning the carrier concentration for thermoelectrical application in the quaternary Heusler compound Co2TiAl(1−x)Six
2010
The family of half-metallic ferromagnets Co2TiZ exhibits exceptional transport properties. The investigated compounds Co2TiAl(1−x)Six (x = 0.25, 0.5, 0.75) show Curie temperatures (TCs) that vary between 250 and 350 K, depending on the composition. Above TC the Seebeck coefficient remains constant. This makes them promising candidates for thermoelectric devices such as thermocouples with a tunable working range. The electrical resistivity data show an anomaly at TC which is attributed to changes in the electronic structure and therefore in the carrier concentration.
Phase separation in the quaternary Heusler compound CoTi(1−x)MnxSb – A reduction in the thermal conductivity for thermoelectric applications
2010
We investigate the phase separation of the solid solution CoTi(1−x)MnxSb into the two Heusler compounds CoTiSb and CoMnSb. Energy-dispersive X-ray spectroscopy measurements on the two-phase material reveal the presence of size- and shape-tunable CoTiSb regions in a CoMnSb matrix. We demonstrate that the formed phase and grain boundaries have a considerable influence on the phonon scattering processes, which leads to a reduction in the thermal conductivity by a factor of three compared to single-phase CoTiSb.
Enhanced Debye level in nano Zn1+xSb, FeSb2, and NiSb: Nuclear inelastic spectroscopy on121Sb
2014
The121 Sb partial density of phonon states (DPS) in nanopowder antimonides were obtained with nuclear inelastic scattering on , , and NiSb prepared by a wet chemistry route. The DPS is compared with the bulk counterpart. An increase of the Debye level indicative of a decrease of the isothermal speed of sound is systematically observed. This observation reveals that the decrease in speed of sound observed in nanostructured thermoelectric materials is not restricted to sintered nanocomposites.
Optimum Carrier Concentration in n-Type PbTe Thermoelectrics
2014
Taking La- and I-doped PbTe as an example, the current work shows the effects of optimizing the thermoelectric figure of merit, zT, by controlling the doping level. The high doping effectiveness allows the carrier concentration to be precisely designed and prepared to control the Fermi level. In addition to the Fermi energy tuning, La-doping modifies the conduction band, leading to an increase in the density of states effective mass that is confirmed by transport, infrared reflectance and hard X-ray photoelectron spectroscopy measurements. Taking such a band structure modification effect into account, the electrical transport properties can then be well-described by a self-consistent single…
Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices
2016
Thermoelectric modules based on half-Heusler compounds offer a cheap and clean way to create eco-friendly electrical energy from waste heat. Here we study the impact of the period composition on the electrical and thermal properties in non-symmetric superlattices, where the ratio of components varies according to (TiNiSn)���:(HfNiSn)���������, and 0 ��� n ��� 6 unit cells. The thermal conductivity (��) showed a strong dependence on the material content achieving a minimum value for n = 3, whereas the highest value of the figure of merit ZT was achieved for n = 4. The measured �� can be well modeled using non-symmetric strain relaxation applied to the model of the series of thermal resistanc…