P-type Thermoelectric Materials Research Articles

Heavy elemental compound addition enhancing thermoelectric performance of Chromium Silicide synthesized by Spark plasma sintering

Silicide-based materials drive great potential in developing mid-temperature range thermoelectric generators (TEGs) applications. However, realizing the efficient and stable silicide materials is still a constraint for its real potential device applications. Chromium silicide will likely become p-type thermoelectric materials in this direction for thermoelectric power generation applications. However, high thermal conductivity values impede the figure-of-merit (zT). The present work adopts the chromium silicide, adding different weight percentages of well-known ZrCoSbSn compounds employing the compaction spark plasma sintering (SPS) technique. By adopting these combinations, the thermal conductivity is significantly reduced by enhanced scattering of heat-carrying phonons by multiple interfaces. Also, the maximum power factor value of ≃ 2.1 x 10-3 W/mK2 is achieved by employing a CrSi2 -ZrCoSbSn compound addition. The enhanced figure-of-merit value (zT) ≃ 0.26 is realized in the temperature at 623 K for the CrSi2-5wt% ZrCoSbSn compound material.

Ultra-Low Thermal Conductivity and Improved Thermoelectric Performance in Tungsten-Doped GeTe.

Compared to SnTe and PbTe base materials, the GeTe matrix exhibits a relatively high Seebeck coefficient and power factor but has garnered significant attention due to its poor thermal transport performance and environmental characteristics. As a typical p-type IV-VI group thermoelectric material, W-doped GeTe material can bring additional enhancement to thermoelectric performance. In this study, the introduction of W, Ge1-xWxTe (x = 0, 0.002, 0.005, 0.007, 0.01, 0.03) resulted in the presence of high-valence state atoms, providing additional charge carriers, thereby elevating the material's power factor to a maximum PFpeak of approximately 43 μW cm-1 K-2, while slightly optimizing the Seebeck coefficient of the solid solution. Moreover, W doping can induce defects and promote slight rhombohedral distortion in the crystal structure of GeTe, further reducing the lattice thermal conductivity κlat to as low as approximately 0.14 W m-1 K-1 (x = 0.002 at 673 K), optimizing it to approximately 85% compared to the GeTe matrix. This led to the formation of a p-type multicomponent composite thermoelectric material with ultra-low thermal conductivity. Ultimately, W doping achieves the comprehensive enhancement of the thermoelectric performance of GeTe base materials, with the peak ZT value of sample Ge0.995W0.005Te reaching approximately 0.99 at 673 K, and the average ZT optimized to 0.76 in the high-temperature range of 573-723 K, representing an increase of approximately 17% compared to pristine GeTe within the same temperature range.

Structure relations with transport properties in p-type thermoelectric materials: Iron silicides

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe1-xMnxSi2 (0≤x≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe2Si5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi2) through heat treatment. The amount of β-FeSi2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (nH of holes) but decrease the mobility (μH). By substituting Mn to β-FeSi2, the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties.

Enhanced thermoelectric performance of Cu2SnSe3 by synergic effects via cobalt-doping

Diamond-like Cu2SnSe3 has drawn intensive attention as an excellent environmentally-friendly p-type thermoelectric material. In this study, the effects of Co-doping at Sn site on its thermoelectric properties were investigated. Results revealed an effective increase in carrier concentration and enhancement of density-of-states (DOS) effective mass m* due to the role of Co as acceptor and probably the contribution of its d states in the valence bands. Consequently, a remarkable power factor of up to 9.55 μW cm−1 K−2 has been achieved at 823 K. In addition, lattice thermal conductivity was strongly suppressed due to the intensified phonon scattering and softening of bonding as revealed by the sound velocity analysis. Ultimately, a maximal ZT of 0.97 at 823 K and an average ZT of ∼ 0.7 have been achieved in Cu2Sn0.88Co0.12Se3, almost double that of the pristine one.

Copper-Enriched Nanostructured Conductive Thermoelectric Copper(I) Iodide Films Obtained by Chemical Solution Deposition on Flexible Substrates

The objects of our research are flexible thin-film thermoelectric materials with nanostructured CuI layers 0.5–1.0 μm thick, fabricated by the chemical solution method Successive Ionic Layer Adsorption and Reaction (SILAR) on flexible polyethylene terephthalate and polyimide substrates. These cubic γ-CuI films differ from films obtained by other chemical solution methods, such as spin-coating, sputtering, and inject printing, in their low resistivity due to acceptor impurities of sulfur and oxygen introduced into CuI from aqueous precursor solutions during SILAR deposition. Energy barriers at the boundaries of 18–22 nm CuI nanograins and a large number of charge carriers inside the nanograins determine the transport properties in the temperature interval 295–340 K characterized by transitions from semiconductor to metallic behavior with increasing temperature, which are typical of nanostructured degenerate semiconductors. Due to the resistivity of about 0.8 mΩ· m at 310 K and the Seebeck coefficient 101 μV/K, the thermoelectric power factor of the CuI film 1.0 μm thick on the polyimide substrate is 12.3 μW/(m · K2), which corresponds to modern thin-film p-type thermoelectric materials. It confirms the suitability of CuI films obtained by the SILAR method for the fabrication of promising inexpensive non-toxic flexible thermoelectric materials.

A nanoscale perspective of the coexistence of multidimensional defects in the AgCuTe system

AgCuTe, a p-type medium-temperature thermoelectric material, exhibits great potential as a candidate for converting waste heat into electricity owing to its low thermal conductivity and high thermoelectric performance. However, an unstable phase structure of the material system has hindered the direct observation of various point defects contacting with high performance, despite their predicted possibilities solely based on first-principles calculations. Here, we present the novel observation of Te interstitial atoms together with other point defects, planar defects, and nanoscale atomic aggregation for the first time in the Zn-doped and Te non-stoichiometric AgCuTe system, employing a nanoscale perspective. Through our investigation, we disclose the remarkable coexistence of multidimensional defects, thereby resolving the previously conflicting opinions regarding point defects in this system. The effective control of these defects is crucial for achieving high thermoelectric performance. The ZnCu point defects regulate carrier concentration and Seebeck coefficient by influencing phase proportion and carrier effective mass. While maintaining the material's inherently large power factor (PF), thermal conductivity is effectively reduced through grain refinement and multiscale defect scattering. As a result, the dimensionless thermoelectric figure of merit (ZT) of approximately ∼ 1.16 is achieved at 773 K. By altering Te content, a coexistence of diverse defects is introduced, leading to intricate microstructures and phase structures. Consequently, a significant reduction in thermal conductivity is observed. The coexistence of multidimensional defects, as well as their impact on microstructure and thermoelectric transport properties, holds significant implications for the performance control of functional materials.

Determination of electrical and thermal conductivities of n- and p-type thermoelectric materials by prediction iteration machine learning method

Synthesising a novel high-performance thermoelectric (TE) material is time-consuming because different compositions of the chemical elements are usually varied using a trial-and-error approach. Moreover, the characterisation of TE materials requires both complex and expensive equipment; these measuring devices often fail during operation. Machine learning (ML) models can be used to accurately predict the properties of a novel composition, saving time as well as the cost of the material and equipment. In this study, two different prediction scenarios have been demonstrated, one for n-type with the general formula BixBayBzYbtTe3, and another for p-type with the general formula SbxBiyBazBtYbwTe3. From the experimental data of the above-mentioned n- and p-type compounds, transport properties of n-type Bi2-xTe3 and p-type Sb1.5Bi0.5-xTe3, where x ranges from 0 to 0.5, involving content variations of Ba, B, and Yb, are predicted. Case 1 deals with the prediction of resistivity and Seebeck values, while case 2 predicts the heat capacity (Cp) and thermal diffusivity values of the n- and p-type TE materials. Herein, different compositions of n-type BixBayBzYbtTe3 and p-type SbxBiyBazBtYbwTe3 are synthesised, and the experimental data are fed to 26 ML models. After training all the ML models, an Artificial Neural Networks (ANN) ML model with the highest R2 values of 0.9943 and 0.9995 in cases 1 and 2, respectively, is found to outperform the other models. The prediction iteration method is applied to the ANN to predict the transport properties of the p-type Sb1.5Bi0.2Ba0.3Te3 and n-type Bi1.9Ba0.1Te3. The accuracy of the prediction iteration method increases with the number of iterations. At the end of the 100th iteration, the prediction error of the ANN model in case 1 is as low as 7%, while it is 9% in case 2.

Thermoelectric performance optimization of GeMnSbTe compounds through increasing the Mn solid solubility: Effects of the co-doping of rare earth elements

GeTe is a p-type thermoelectric (TE) material that exhibits a high ZT value and holds promise for a wide range of applications. In this study, a series of Ge0.86Mn0.1Sb0.04Te + 1 mol.% RE (Rare Earth elements = Er, Tm, Yb, Lu) compounds are synthesized through the melt-quenching method followed by fast-hot-pressing. Findings indicate that the TE properties are improved by simultaneously increasing the Seebeck coefficient and reducing the thermal conductivity, making the peak ZT value experiences an enhancement of 73%, while the average ZT value through 450–800 K shows an improvement of 70%. The solid solubility of Mn is significantly increased by the addition of the REs, that promotes the regulating effect of Mn on the energy band. A diverse range of microstructures including ordered atomic staggered arrays, van der Waals interstitials, dislocation enrichment, dislocation networks, nano precipitation phases with cavity structures, interstitial clusters, and vacancy clusters are introduced by REs, significantly contributing to the reduction of the κL. Thus, this study offers valuable insights and mechanism analysis into enhancing the properties of GeMnSbTe materials by incorporating REs, and proves that Tm has better thermoelectric performance optimization effect in this.

Thermoelectric properties of cement mortar doped with steel fiber under heating conditions

In order to supply the multifunctional demand for building materials in modern construction industry, research on the thermoelectric properties of cement mortar mixed with steel fibers (diameter 0.22 mm) for engineering purposes has been carried out in this paper. The self-built thermoelectric response test system is used to collect the thermoelectric power, surface temperature and conductivity of the cement-based composite specimens in real time. Based on the comparative measurement method, the thermal conductivity of large-sized specimens was obtained. The effect of different SF content on thermal conductivity, Seebeck coefficient and ZT of the specimens were investigated. The results show that the specimens doped with steel fiber is p-type thermoelectric material, and the maximum value of thermoelectric figure of merit ZT of the cement mortar doped with 7.5 wt% steel fiber at 50℃ is 0.175. The ZT of cement mortar specimens mixed with steel fibers is relatively low, but it has good application prospects as a low-cost and widely used building material.

Thermoelectric Sensor with CuI Supported on Rough Glass.

Thermoelectric generators convert heat into a potential difference with arrays of p- and n-type materials, a process that allows thermal energy harvesting and temperature detection. Thermoelectric sensors have attracted interest in relation to the creation of temperature and combustible gas sensors due to their simple operation principle and self-powering ability. CuI is an efficient p-type thermoelectric material that can be readily produced from a Cu layer by an iodination method. However, the vapor iodination of Cu has the disadvantage of weak adhesion on a bare glass substrate due to stress caused by crystal growth, limiting microfabrication applications of this process. This work presents a rough soda-lime glass substrate with nanoscale cavities to support the growth of a CuI layer, showing good adhesion and enhanced thermoelectric sensitivity. A rough glass sample with nanocavities is developed by reactive ion etching of a photoresist-coated glass sample in which aggregates of carbon residuals and the accumulation of NaF catalyze variable etching rates to produce local isotropic etching and roughening. A thermoelectric sensor consists of 41 CuI/In-CoSb3 thermoelectric leg pairs with gold electrodes for electrical interconnection. A thermoelectric leg has a width of 25 μm, a length of 3 mm, and a thickness of 1 μm. The thermoelectric response results in an open-circuit voltage of 13.7 mV/K on rough glass and 0.9 mV/K on bare glass under ambient conditions. Rough glass provides good mechanical interlocking and introduces important variations of the crystallinity and composition in the supported thermoelectric layers, leading to enhanced thermopower.

Controlling the thermoelectric properties of organo-metallic coordination polymers through backbone geometry.

Poly(nickel-benzene-1,2,4,5-tetrakis(thiolate)) (Ni-btt), an organometallic coordination polymer (OMCP) characterized by the coordination between benzene-1,2,4,5-tetrakis(thiolate) (btt) and Ni2+ ions, has been recognized as a promising p-type thermoelectric material. In this study, we employed a constitutional isomer based on benzene-1,2,3,4-tetrakis(thiolate) (ibtt) to generate the corresponding isomeric polymer, poly(nickel-benzene-1,2,3,4-tetrakis(thiolate)) (Ni-ibtt). Comparative analysis of Ni-ibtt and Ni-btt reveals several common infrared (IR) and Raman features attributed to their similar square-planar nickel-sulfur (Ni-S) coordination. Nevertheless, these two polymer isomers exhibit substantially different backbone geometries. Ni-btt possesses a linear backbone, whereas Ni-ibtt exhibits a more undulating, zig-zag-like structure. Consequently, Ni-ibtt demonstrates slightly higher solubility and an increased bandgap in comparison to Ni-btt. The most noteworthy dissimilarity, however, manifests in their thermoelectric properties. While Ni-btt exhibits p-type behavior, Ni-ibtt demonstrates n-type carrier characteristics. This intriguing divergence prompted further investigation into the influence of OMCP backbone geometry on the electronic structure and, particularly, the thermoelectric properties of these materials.

Thermoelectric properties of Gd and Se double substituted tetrahedrite.

The compound Cu12Sb4S13, known as tetrahedrite, is an eco-friendly p-type thermoelectric material with earth-abundant, low-cost, and less toxic constituents. This contemporary work studied the thermoelectric properties of Gd and Se double-substituted tetrahedrites. The samples with nominal composition Cu11.95Gd0.05Sb4S13-xSex (where x = 0, 0.2, 0.4, 0.6, and 0.8) were prepared using the solid-state synthesis and sintered using high vacuum hot pressing. The structural analysis using X-ray diffraction revealed a successful tetrahedrite phase formation, and the systematic increase of lattice parameters with the selenium content (x) indicated successful Se substitution. The electron probe microanalysis revealed the presence of secondary phases Cu3SbS4, CuSbS2, and CuGdS2. The Raman spectroscopy showed a weakening Sb-S/Se bond with increased Se content in the samples. The +3 and -2 oxidation states of Gd and Se, respectively, were confirmed from the XPS study. Gd3+, a higher valence substituent at the Cu+/Cu2+ tetrahedral site, helped reduce the carrier concentration. On the other hand, the isoelectronic substitution of Se2- for S2- enhanced the thermopower and power factor by introducing resonant energy states near the Fermi level. Consequently, a maximum power factor of ∼1.35 (±0.08) mW m-1 K-2 at ∼729 K was obtained for the sample x = 0.4. The sample x = 0.4 also exhibited the lowest thermal conductivity ∼ 1.18 (±0.04) W m-1 K-1 at 729 K. The Callaway model indicates that the lowering in the lattice thermal part of conductivity of this sample is due to the combined effect of point defect and Umklapp scattering. The simultaneous improvement of carrier concentration and thermal conductivity resulted in a relatively high zT of ∼0.83 (±0.09) in the x = 0.4 sample.

Production of (Fe,Co)Si2 and (Fe.Mn)Si2 Thermoelectric Materials by Spark Plasma Sintering

In this study, FeSi2 bulk specimens were prepared by mechanical alloying, spark plasma sintering, and subsequent annealing. The annealed FeSi2 bulk specimens consisted of the β-FeSi2 phase and exhibited high Seebeck coefficient values. The maximum Seebeck coefficient of 356 μVK−1 was achieved in the FeSi2 bulk specimen annealed at 1173 K for 6 h. However, the power factor of the FeSi2 bulk specimen was quite small due to its high electrical resistivity, and a drastic improvement is required. Therefore, Mn- and Co-substituted specimens, Fe1−xMnxSi2 (x = 0.2–0.8) and Fe1−xCoxSi2 (x = 0.2–0.8), were produced, and their thermoelectric properties were evaluated. The Mn- and Co-substituted specimens exhibited lower electrical resistivity and a higher power factor than the FeSi2 bulk specimen. The Fe1−xMnxSi2 (x = 0.2–0.8) bulk specimens were p-type thermoelectric materials, and a Seebeck coefficient of 262 μVK−1 and a power factor of 339 μWm−1K−2 were achieved in the Fe0.94Mn0.06Si2 bulk specimen. On the other hand, the Fe1−xCoxSi2 (x = 0.2–0.8) bulk specimens were n-type thermoelectric materials, and a Seebeck coefficient of −180 μVK−1 and a power factor of 667 μWm−1K−2 were achieved in the Fe0.96Co0.04Si2 bulk specimen.

Band Engineering Through Pb-Doping of Nanocrystal Building Blocks to Enhance Thermoelectric Performance in Cu3 SbSe4.

Developing cost-effective and high-performance thermoelectric (TE) materials to assemble efficient TE devices presents a multitude of challenges and opportunities. Cu3 SbSe4 is a promising p-type TE material based on relatively earth abundant elements. However, the challenge lies in its poor electrical conductivity. Herein, an efficient and scalable solution-based approach is developed to synthesize high-quality Cu3 SbSe4 nanocrystals doped with Pb at the Sb site. After ligand displacement and annealing treatments, the dried powders are consolidated into dense pellets, and their TE properties are investigated. Pb doping effectively increases the charge carrier concentration, resulting in a significant increase in electrical conductivity, while the Seebeck coefficients remain consistently high. The calculated band structure shows that Pb doping induces band convergence, thereby increasing the effective mass. Furthermore, the large ionic radius of Pb2+ results in the generation of additional point and plane defects and interphases, dramatically enhancing phonon scattering, which significantly decreases the lattice thermal conductivity at high temperatures. Overall, a maximum figure of merit (zTmax ) ≈ 0.85 at 653 K is obtained in Cu3 Sb0.97 Pb0.03 Se4 . This represents a 1.6-fold increase compared to the undoped sample and exceeds most doped Cu3 SbSe4 -based materials produced by solid-state, demonstrating advantages of versatility and cost-effectiveness using a solution-based technology.

Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn2VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn2VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect. For practical use, the Seebeck coefficient S of Mn2VAl should be increased while maintaining a high electrical conductivity σ from its half-metallic character. Herein, we achieved this objective through antisite defect engineering. Theoretically, it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect, fAD, between V and Al atoms in Mn2VAl. Experimentally, a significant increase in S and a slight decrease in σ were observed for an Mn2VAl sample with an optimal fAD = 33%, enhancing the thermoelectric power factor PF by 2.7 times from an Mn2VAl sample with fAD = 14%. Furthermore, we combined the antisite defect engineering with a partial substitution method. An Mn2V(Al0.96Si0.04) sample with fAD = 33% exhibited the highest PF = 4.5 × 10−4 W·m−1·K−2 at 767 K among the samples. The maximum dimensionless figure-of-merit zT of the Mn2V(Al0.96Si0.04) sample with fAD = 33% was measured to be 3.4 × 10−2 at 767 K, which is the highest among the p-type half-metallic full-Heusler alloys.

Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl2Te4 monolayer

Inspired by the excellent stability exhibited by experimentally synthesized two-dimensional (2D) MoSi2N4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl2Te4 monolayer are systematically investigated using the First-principles calculations and Boltzmann transport theory. The mechanical stability, dynamic stability, and thermal stability (900 K) of the MgAl2Te4 monolayer are demonstrated, respectively. The MgAl2Te4 monolayer exhibits a bandgap of 1.35 eV using the HSE06 functional in combination with spin-orbit coupling (SOC) effect. Band convergence in the valence band is favorable to improve the thermoelectric properties. The rattling thermal damping effect caused by the weak bonding of MgTe bonds in MgAl2Te4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/(m·K)@300 K along the x-/y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Grüneisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl2Te4 monolayer, showing the great promising prospect for the excellent p-type thermoelectric material. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties, but also elaborates on the promising thermoelectric application of MgAl2Te4 monolayer material at high temperature.

High-throughput deformation potential and electrical transport calculations

The deformation potential plays an important role in electrical transport properties, but in the context of high-throughput searches requires a consistent and readily computable reference level. Here, we design a high-throughput method for calculating the deformation potential for semiconductors in the MatHub-3d database. The deformation potential is obtained from the volume-dependent band edge (valence band maximum and conduction band minimum) variations with respect to the reference level. In order to adapt the calculation of reference level to a high-throughput manner, the average value of the first valence electron energy band associated with each compound is used as the reference level. Deformation potentials for 11,993 materials are calculated using the above-mentioned method. By considering the calculated deformation potentials, electronic structures, and bulk moduli, 9957 compounds with converged electrical transport properties are obtained. 332 promising p-type thermoelectric materials, and 321 n-type entries are then proposed. Among them, 156 compounds are screened to having both potentially good n- and p-type thermoelectric transport properties. The band structures and chemical bonding information for several typical compounds are further presented to reveal favorable band and bonding features for thermoelectrics.

Enhancing Thermoelectric Performance of CuInTe2 via Trace Ag Doping at Indium Sites.

Thermoelectric technology can be utilized to directly convert waste heat into electricity, aiming at energy harvesting in an environmentally friendly manner. As a promising p-type thermoelectric material, CuInTe2 possesses a high inherent lattice thermal conductivity, which limits the practical implementation in the field of thermoelectricity. Herein, through the combination of vacuum melting and annealing along with hot-pressure sintering techniques, we demonstrated that CuIn0.95Ag0.05Te2 thermoelectric materials with trace Ag doping can exhibit a notably high Seebeck coefficient of 614 μV/K, arising from the high density-of-states effective mass and reduced carrier concentration. Owing to the diminished lattice thermal conductivity derived from Umklapp scattering induced by point defects and dislocation, stemming from the trace Ag doping at In sites rather than Cu sites, CuIn0.95Ag0.05Te2 exhibited a maximum figure of merit (ZT) of 1.38 at 823 K, an 18% enhancement over pristine CuInTe2, leading to a maximum average ZT of 0.67 across temperatures ranging from 303 to 823 K. In essence, our work underscores the efficacy of doping engineering and point defects in tailoring the thermoelectric performance of CuInTe2-based materials. This study not only contributes to advancing the fundamental understanding of thermoelectric enhancement but also lays out a practical pathway toward the realization of high-performance CuInTe2-based thermoelectric materials.

Realizing the Ultralow Lattice Thermal Conductivity of Cu3SbSe4 Compound via Sulfur Alloying Effect.

Cu3SbSe4 is a potential p-type thermoelectric material, distinguished by its earth-abundant, inexpensive, innocuous, and environmentally friendly components. Nonetheless, the thermoelectric performance is poor and remains subpar. Herein, the electrical and thermal transport properties of Cu3SbSe4 were synergistically optimized by S alloying. Firstly, S alloying widened the band gap, effectively alleviating the bipolar effect. Additionally, the substitution of S in the lattice significantly increased the carrier effective mass, leading to a large Seebeck coefficient of ~730 μVK-1. Moreover, S alloying yielded point defect and Umklapp scattering to significantly depress the lattice thermal conductivity, and thus brought about an ultralow κlat ~0.50 Wm-1K-1 at 673 K in the solid solution. Consequently, multiple effects induced by S alloying enhanced the thermoelectric performance of the Cu3SbSe4-Cu3SbS4 solid solution, resulting in a maximum ZT value of ~0.72 at 673 K for the Cu3SbSe2.8S1.2 sample, which was ~44% higher than that of pristine Cu3SbSe4. This work offers direction on improving the comprehensive TE in solid solutions via elemental alloying.

Impact of Lu-Substitution in Yb14-xLuxZnSb11: Thermoelectric Properties and Oxidation Studies.

Yb14ZnSb11 is one of the newest additions to the high-performance Yb14MSb11 (M = Mn, Mg, and Zn) family of p-type high-temperature thermoelectric materials and shows promise for forming passivating oxide coatings. Work on the oxidation of rare earth (RE)-substituted Yb14-xRExMnSb11 single crystals suggested that substituting late RE elements may form more stable passivation oxide coatings. Yb14-xLuxZnSb11 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7) samples were synthesized, and Lu-substitution's effects on thermoelectric and oxidation properties are investigated. The solubility of Lu within the system was found to be quite low with xmax ∼ 0.3; samples with x > 0.3 contained impurities of LuSb. Goldsmid-Sharp band gap estimations show that introducing Lu reduces the apparent band gap. Because of this, the Lu-substituted samples show a reduction in the maximum Seebeck coefficient, decreasing the high-temperature zT. This contrasts with the impact of Lu3+ substitution in Yb14MnSb11, where the addition of Lu3+ for Yb2+ results in increases in both resistivity and the Seebeck coefficient. Oxidation of the x = 0.3 solid solution was studied by thermogravimetric- differential scanning calorimetry , powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, and optical images. The samples show no mass gain before 785 K, and ensuing oxidation reactions are proposed. At the highest temperatures, significant amounts of Yb14-xLuxZnSb11 remained beneath an oxide coating, suggesting that passivation may be achievable in oxygen environments.