Thermoelectric Performance of the Half-Heusler Phases RNiSb ( R=Sc,Dy,Er,Tm,Lu ): High Mobility Ratio between Majority and Minority Charge Carriers (original) (raw)
Related papers
Physical Review Applied
Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelectric materials discovery. Using its product-mobility ratio between electrons and holes-it is possible to choose the most promising compound from the series and pave the correct direction of doping. Current work presents positive verification of this approach for ScNiSb, which is anticipated to show superior mobility when tuned towards n-type behavior. In agreement with expectation, the mobility increases by an order of magnitude due to rising tellurium content in the ScNiSb 1−x Te x series. The effect is most likely driven by change of the dominant charge carriers' scattering mechanism from ionized impurity influence to point defect and acoustic phonon interaction. Simultaneously, due to a highly anisotropic conduction band, the effective mass of the carriers rises towards the n-type regime. These two effects lead to an improved thermoelectric power factor of electron-doped samples, up to 40 μWK −2 cm −1 at 740 K for ScNiSb 0.85 Te 0.15. Based on this result, we suggest n-type doping for other rare-earth-based half-Heusler compounds. Representatives of this group exhibit the smallest lattice thermal conductivity in the pristine form among any half-Heusler thermoelectrics, and are anticipated to show comparably good electrical properties to ScNiSb due to their high mobility ratio in favor of electrons.
ACS Applied Energy Materials
We report first-principle calculations of the recently synthesized Pb-free double perovskite Cs 2 PtI 6 , which we found to have the potential to be an excellent thermoelectric material, through the investigation of its electronic and phonon transport properties. The Heyd−Scuseria−Ernzerhof functional results in an indirect band gap of 1.40 eV, perfectly matching the experiment. Our well-converged phonon dispersion displays positive frequencies in the entire Brillouin zone and hence confirms the dynamic stability of the material. Further, the low-lying optical modes mix significantly with the heat-carrying acoustic phonons and add to their scattering phase space. We have found strong phonon anharmonicity due to the nonsymmetric and nonspherical electron densities of the atoms derived from their bonding environment, which in combination with low group velocities and high phonon scattering rates results in ultralow lattice thermal conductivity in Cs 2 PtI 6. For example, it is 0.15 W/mK at 300 K, which is 8-fold smaller than that reported for the typical thermoelectric material Bi 2 Te 3. Our simulations show that it could be reduced by another factor of 2 by nanostructuring the material with features of around 8 nm. We have found a remarkably high p-type Seebeck coefficient of 139 μV/K at the maximum considered carrier concentration and temperature. Our calculations also find a high figure of merit of 1.03 for the p-type carriers at room temperature, attributed to the substantial thermoelectric coefficient S 2 σ/τ, where S, σ, and τ are the Seebeck coefficient, the electrical conductivity, and the relaxation time, respectively.
Electrical and thermal transport property studies of high-temperature thermoelectric materials
1984
The first year of this research emphasized the study of electronically conducting oxides with varied transport characteristics, an evaluation of theoretical models, and the determination of a high-temperature transport property data base. Oxide systems based on SnO2-In2O3, (La, Y) (Mg,Ca,Sr) CrO3, HfO2-RxOy-In3O3 and La(Sr)MnO3 were selected for initial studies and represent different crystallographic/defect structures and transport characteristics. The electrical conductivity, Seeback coefficient and thermal conductivity for these oxides are being measured and have provided a preliminary data base for evaluating transport properties and the figure of merit. The purpose of this report is to describe the technical results obtained during the first year's study of high-temperature thermoelectric materials. The scope of the research is (1) to develop theoretical models for electrical, thermal, and thermoelectric behavior of refractory oxide materials, (2) to determine electrical t...
High-temperature charge and thermal transport properties of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:min-type thermoelectric material PbSe
Physical Review B, 2011
We present a detailed study of the charge transport, optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustical phonon scattering alone. We applied the first order non-parabolicity approximation to extract the density of states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in the light of doping dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows strong deviation from the expected Debye-Peierls high temperature behavior (umklapp dominated) indicating an additional heat carrying channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of ∼ 0.8 at 700K at ∼ 1.5 × 10 19 cm −3. I.
Thermal Conductivity in Thermoelectric Materials
Updates on Thermoelectricity [Working Title]
Thermal conductivity is a key parameter in identifying and developing alternative materials for many technological and temperature-critical applications, ranging from higher-temperature capability thermal barrier coatings to materials for thermoelectric conversion. The Figure of Merit (ZT) of a thermoelectric material (TE) is a function of the Seebeck coefficient (S), the electrical conductivity (σ), the total thermal conductivity (κ) and the absolute temperature (T). A highly-performing TE material should have high S and σ and low κ. Thermal conductivity has two contributions, the electronic (κE) and the lattice (κL). Various models have been developed to describe the lattice component of thermal conductivity. In this chapter, the models for the evaluation of lattice thermal conductivity will be explored, both phenomenological as well analytical models, taking into account the various phonon-scattering processes, with examples of real materials.
Extrapolation of Transport Properties and Figure of Merit of a Thermoelectric Material
Energies, 2015
The accurate determination of the thermoelectric properties of a material becomes increasingly difficult as the temperature rises. However, it is the properties at elevated temperatures that are important if thermoelectric generator efficiency is to be improved. It is shown that the dimensionless figure of merit, ZT, might be expected to rise with temperature for a given material provided that minority carrier conduction can be avoided. It is, of course, also necessary that the material should remain stable over the whole operating range. We show that the prediction of high temperature properties in the extrinsic region is possible if the temperature dependence of carrier mobility and lattice thermal conductivity are known. Also, we show how the undesirable effects arising from mixed or intrinsic conduction can be calculated from the energy gap and the relative mobilities of the electrons and the positive holes. The processes involved are discussed in general terms and are illustrated for different systems. These comprise the bismuth telluride alloys, silicon-germanium alloys, magnesium-silicon-tin and higher manganese silicide.
Thermoelectric properties of IV–VI-based heterostructures and superlattices
Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n < 10^18 cm^-3). A large value of ZT|| (parallel to the growth direction) of 3.0 is predicted for n = 4.7 x 10^18 cm^-3 and T = 700 K, whereas ZT_p (perpendicular to the growth direction) is found to peak at 1.5 for n = 1.7 x 10^17 cm^-3. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed.
THERMOELECTRIC PROPERTIES OF p-TYPE
2012
In the present study, thermoelectric materials based on p-type 3 2Te Bi and dispersed ingots were prepared by using standard solid-state microwave synthesis procedures. The microstructures of the ingots were characterized by field emission scanning electron microscopy. The crystalline of the powders were examined by X-ray diffraction, which showed the formation of a rhombohedral structure. The electrical transport properties of the samples were studied from room temperature up to 500K. The results indicate that the hole concentration gradually increases, resulting in an increase in electrical conductivity and a decrease in the Seebeck coefficient with increasing Se content. The