Typical Thermoelectric Materials Research Articles

Thermoelectric Transport Properties of Sb-doped SnSe<sub>2</sub> Polycrystalline Alloys

SnSe<sub>2</sub> alloys have been investigated in recent times as potential <i>n</i>-type thermoelectric materials. In this study, the thermoelectric transport properties of a series of Sb-doped SnSe<sub>2</sub>, Sn(Se<sub>1-x</sub>Sb<sub>x</sub>)<sub>2</sub> (<i>x</i> = 0, 0.015, 0.03, 0.045, 0.06) alloys are investigated. The electrical conductivity was generally enhanced with Sb doping owing to a large increase in electron concentration. However, the Seebeck coefficient largely decreased with doping. Consequently, the power factor was significantly lower at a low doping of <i>x</i> = 0.015, and then began rising as the doping was increased beyond <i>x</i> = 0.015. It was found that the density-of-states effective mass and weighted mobility decreased with Sb doping, implying that the electrical transport properties of SnSe<sub>2</sub> were degraded by Sb doping. The total and lattice thermal conductivities gradually decreased due to additional point defect scattering. Thus, the thermoelectric figure of merit declined significantly, from 0.30 of the pristine sample with a low doping of Sb (<i>x</i> = 0.015) at 750 K, to 0.18, and then for <i>x</i> = 0.06 it gradually recovered to the value of the undoped sample. The thermoelectric quality factor decreased as the Sb doping was increased, implying that Sb doping did not enhance the thermoelectric transport properties, despite the large increase in electron concentration.

Mechanically Adaptative and Environmentally Stable Ionogels for Energy Harvest.

Converting building and environment heat into electricity is a promising strategy for energy harvest to tackle global energy and environmental problems. The processing challenges, mechanical brittleness, and low environmental tolerance of typical thermoelectric materials, however, prevent them from realizing their full potential when employed in outdoor building systems. Herein, a general concept based on synergistic ionic associations to significantly improve the mechanical properties and harsh environment stability for high-performance ionic-type thermoelectric (i-TE) gels is explored. They demonstrate extraordinarily high stretchability (1300-2100%), fast self-healing (120 s), temperature insensitivity, and great water-proof performance, and could be painted on a variety of surfaces. The n-type ionic Seebeck coefficient is up to -8.8mV K-1 and the ionic conductivity is more than 0.14 mS cm-1 . Both exhibit remarkable thermal and humidity stability (293-333 K, 20-100 RH%), which are rarely achieved in previous studies. Even on a cloudy day, the open-circuit thermovoltage for a painted i-TE array with an area of about 8.5 × 10-3 m2 is above 2V. This research offers a promising approach for gathering significant waste heat and even solar energy on outside building surfaces in an effective and sustainable manner.

Inhibiting the bipolar effect via band gap engineering to improve the thermoelectric performance in n-type Bi2-Sb Te3 for solid-state refrigeration

• Se replacement can enlarge the E g and thus effectively mitigate the bipolar effect. • The manipulation of donor-like effect retains the optimized carrier concentration. • The large strain field and mass fluctuation reduce lattice thermal conductivity. • A state-of-the-art zT = 1.0 at 300 K is attained for n -type Bi 1.5 Sb 0.5 Te 2.8 Se 0.2 . • n -type Bi 2- x Sb x Te 3 becomes a promising candidate for solid-state cooling field. To date, the benchmark Bi 2 Te 3 -based alloys are still the only commercial material system used for thermoelectric solid-state refrigeration. Nonetheless, the conspicuous performance imbalance between the p -type Bi 2- x Sb x Te 3 and n -type Bi 2 Te 3- x Se x legs has become a major obstacle for the improvement of cooling devices to achieve higher efficiency. In our previous study, novel n -type Bi 2- x Sb x Te 3 alloy has been proposed via manipulating donor-like effect as an alternative to mainstream n -type Bi 2 Te 3- x Se x . However, the narrow bandgap of Bi 2- x Sb x Te 3 provoked severe bipolar effect that constrained the further improvement of zT near room temperature. Herein, we have implemented band gap engineering in n -type Bi 1.5 Sb 0.5 Te 3 by employing isovalent Se substitution to inhibit the undesired intrinsic excitation and achieve the distinguished room-temperature zT . First, the preferential occupancy of Se at Te 2 site appropriately enlarges the band gap, thereby concurrently improving the Seebeck coefficient and depressing the bipolar thermal conductivity. In addition, the Se alloying mildly suppresses the compensation mechanism and essentially preserves the already optimized carrier concentration, which maintains the peak zT near room temperature. Moreover, the large strain field and mass fluctuation generated by Se alloying leads to the remarkable reduction of lattice thermal conductivity. Accordingly, the zT value of Bi 1.5 Sb 0.5 Te 2.8 Se 0.2 reaches 1.0 at 300 K and peaks 1.1 at 360 K, which surpasses that of most well-known room-temperature n -type thermoelectric materials. These results pave the way for n -type Bi 2- x Sb x Te 3 alloys to become a new and promising top candidate for large-scale solid-state cooling applications.

Thermoelectric Response Enhanced by Surface/Edge States in Physical Nanogaps.

Current solid-state thermoelectric converters have poor performance, which typically renders them useless for practical applications. This problem is evidenced by the small figures of merit of typical thermoelectric materials, which tend to be much smaller than 1. Increasing this parameter is then key for the development of functional devices in technologically viable applications that can work optimally. We propose here a feasible and effective design of new thermoelectric systems based on physical gaps in nanoscale junctions. We show that, depending on the type of features, i.e., the character of surface/edge states, on both sides of the gap, it is possible to achieve high figures of merit. In particular, we show that, for configurations that have localized states at the surfaces/edges, which translate into sharp resonances in the transmission, it is possible to achieve large Seebeck coefficients and figures of merit by carefully tuning their energy and their coupling to other states. We calculate the thermoelectric coefficients as a function of different parameters and find non-obvious behaviors, such as the existence of a certain coupling between the localized and bulk states for which these quantities have a maximum. The highest Seebeck coefficients and figures of merit are achieved for symmetric junctions, which have the same coupling between the localized state and the bulk states on both sides of the gap. The features and trends of the thermoelectric properties and their changes with various parameters that we find here can be applied not only to systems with nanogaps but also to many other nanoscale junctions, such as those that have surface states or states localized near the contacts between the nanoscale object and the electrodes. The model presented here can, therefore, be used to characterize and predict the thermoelectric properties of many different nanoscale junctions and can also serve as a guide for studying other systems. These results pave the way for the design and fabrication of stable next-generation thermoelectric devices with robust features and improved performance.

Defect engineering synergistically modulates power factor and thermal conductivity of CuGaTe2 for ultra-high thermoelectric performance

• The vacancy of Cu atom can increase the band gap and reduce the sound velocity. • Cu vacancies increase the density of the samples, and significantly increase the carrier concentration. • Cu vacancies generate many defects, which scatter phonons at multiple scales and realize thermoelectric decoupling. • The highest ZT value of Cu 0.96 GaTe 2 reaches 1.23 at 823 K, and the average ZT value reaches 0.575. The ternary chalcopyrite CuGaTe 2 has emerged as a promising p -type thermoelectric material with its advantages of low cost, good stability, and non-toxic elements. However, its thermoelectric performance is limited by the intrinsic low electrical conductivity and high lattice thermal conductivity. In this work, A deficiency of Cu in Cu 1– x GaTe 2 semiconductors can be used to optimize the electrical properties by improving the carrier concentration and to reduce thermal conductivity through multi-scale phonon scattering, which is predicted and guided by the First-principles density functional theory calculations. The carrier concentration is increased to 10 20 , which compensates for the low electrical performance caused by the intrinsic low n H of CuGaTe 2 . The average power factor of Cu 0.96 GaTe 2 reaches 106.3% higher than that of the original CuGaTe 2 . In addition, the lattice thermal conductivity of the defective samples is greatly reduced at high temperatures, which is mainly due to the reduction of sound speed and phonon scattering. All the above factors contribute to the highest dimensionless figure of merit (ZT) value of 1.23 at 823 K in Cu 0.96 GaTe 2 , which is 114% higher than the pristine CuGaTe 2 , and the average ZT is 171.4% higher.

Topological insulator VxBi1.08-Sn0.02Sb0.9Te2S as a promising n-type thermoelectric material

As one of the most important n -type thermoelectric (TE) materials, Bi 2 Te 3 has been studied for decades, with efforts to enhance the thermoelectric performance based on element doping, band engineering, etc. In this study, we report a novel bulk-insulating topological material system as a replacement for n -type Bi 2 Te 3 materials: V doped Bi 1.08 Sn 0.02 Sb 0.9 Te 2 S (V:BSSTS). The V:BSSTS is a bulk insulator with robust metallic topological surface states. Furthermore, the bulk band gap can be tuned by the doping level of V, which is verified by magnetotransport measurements. Large linear magnetoresistance is observed in all samples. Excellent thermoelectric performance is obtained in the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved in the 2% V doped sample (denoted as V 0.02 ) at 530 K. The high thermoelectric performance of V:BSSTS can be attributed to two synergistic effects: (1) the low conductive secondary phases Sb 2 S 3 , and V 2 S 3 are believed to be important scattering centers for phonons, leading to lower lattice thermal conductivity; and (2) the electrical conductivity is increased due to the high-mobility topological surface states at the boundaries. In addition, by replacing one third of costly tellurium with abundant, low-cost, and less-toxic sulfur element, the newly produced BSSTS material is inexpensive but still has comparable TE performance to the traditional Bi 2 Te 3 -based materials, which offers a cheaper plan for the electronics and thermoelectric industries. Our results demonstrate that topological materials with unique band structures can provide a new platform in the search for new high performance TE materials. • The high conductive topological surface state of the V:BSSTS samples is considered to be responsible for the good thermoelectric behavior. • Low thermal conductivity: Sb 2 S 3 and V 2 S 3 secondary phases effectively scatter phonons leading to low lattice thermal conductivity. • High ZT throughout the whole temperature range: a ZT max of ~0.8 is achieved in the 2% V doped sample, and the ZT values keep high through the whole temperature range.

Bismuth telluride based efficient thermoelectric power generator with electrically conducive interfaces for harvesting low-temperature heat

Nearly 50% of the heat released by various sources in the environment is found in the temperature range below 573 K. Thermoelectric generators (TEGs) offer a robust solid-state energy conversion mechanism to harvest this waste heat into useful electrical energy. To develop efficient TEGs, a prerequisite is to couple n - and p -type thermoelectric materials through metallic interconnect, with low specific contact resistivity ( ρ c ). The realization of low ρ c involves several critical factors, such as the chemical and mechanical stability, which should be carefully optimized to achieve consistent TEG performance under long-term operation. In the present work, we have demonstrated the concept of a graded interface layer to realize electrically conducive contacts in mechanically alloyed n -Bi 2 Te 2.7 Se 0.3 and p -Bi 0.5 Sb 1.5 Te 3 thermoelectric material (TM) having moderate figure-of-merit ( zT ). We have reproducibly achieved electric contacts with low ρ c in these materials (∼59-71 μΩ-cm 2 ) using a graded layer of Ni. Using the established approach, the conversion efficiency ( η exp ) of 6.5% (±10%) is demonstrated for the temperature difference (Δ T ) of 270 K. Achieved η exp in the present work matches well with the simulated conversion efficiency ( η sim )∼7.0%, and is one amongst the best-reported efficiencies surpassing the state-of-the-art commercial modules.

Influence of SiC dispersion and Ba(Sr) substitution on the thermoelectric properties of Ca3Co4O9+δ

Ca 3 Co 4 O 9+δ is a typical p -type thermoelectric oxide material with a low thermal conductivity. In this study, double-layered oxide samples Ca(Ba,Sr) 3 Co 4 O 9+δ dispersed with different SiC contents were obtained via the traditional solid phase reaction method. The effects of different elemental substitutions and SiC dispersion contents on the microstructure and thermoelectric properties of the samples were studied. The double optimisation of partial substitution of Ca-site atoms and SiC dispersion considerably improved the thermoelectric properties of Ca 3 Co 4 O 9+δ . Through the elemental substitution, the resistivity of the Ca 3 Co 4 O 9+δ material was reduced. Conversely, introducing an appropriate amount of SiC nanoparticles enhanced phonon scattering and was crucial in reducing its thermal conductivity. After double optimisations, the dimensionless thermoelectric figure of merit ( ZT ) values of both Ca 2.93 Sr 0.07 Co 4 O 9+δ + 0.1 wt% SiC and Ca 2.9 Ba 0.1 Co 4 O 9+δ + 0.1 wt% SiC achieved an optimum value of 0.25 at 923 K.

Cobalt-based full Heusler compounds Co2FeZ (Z = Al, Si, and Ga): A comprehensive study of competition between XA and L21 atomic ordering with ab initio calculation

To study the structural properties of Co2FeZ (Z = Al, Si, Ga) (CFZ) alloys, we will use the approximation method GGA-PBE based on the method of plane waves increased by linear waves at full potential using the theory of functional density in both the Hg2CuTi and Cu2MnAl-type structures. From the most stable state we determine the other properties such as the magnetic, elastic and thermoelectric properties. The band structure calculation reveals indirect band gap in spin down channel and zero band gap in spin up channel of valence and conduction bands confirming the spin gapless semiconducting nature of these compounds. Calculated Seebeck coefficient in spin up and spin down channel reveals that the CFZ behaves as both n and p type thermoelectric materials with better output efficiency. The transport properties of these materials are discussed on the basis of Seebeck coefficient, electrical conductivity coefficient, thermal conductivity and figure-of-merit coefficient. By analyzing the nature of the bonding between the different atoms that form CFZ that each of them has a strong covalent character.

Honeycomb-like puckered PbTe monolayer: A promising n-type thermoelectric material with ultralow lattice thermal conductivity

Inspired by the superior thermoelectric performance of two-dimensional (2D) materials, the electrical transport and thermoelectric properties of honeycomb-like puckered PbTe monolayer were theoretically evaluated using the first-principles calculations and the semiclassical Boltzmann transport theory. The puckered PbTe monolayer is a direct gap semiconductor with wide bandgap of 2.251 eV within Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional in combination with spin-orbital coupling (SOC) effect. Further analysis of formation energy, elastic constant, and ab initio molecular dynamics (AIMD) simulation prove the thermodynamic, mechanical and thermal stabilities of PbTe monolayer. The low thermal transport, small phonon group velocity, large Grüneisen parameters, and short phonon relaxation time greatly suppress the phonon transport and lead to low lattice thermal conductivity of ∼0.75 and ∼0.79 W/m K along the armchair and zigzag directions at 900 K, respectively. An optimal ZT = ~1.55 at the carrier concentration of 3.94 × 10 12 cm −2 is obtained for PbTe monolayer along zigzag direction at 900 K, which demonstrates the great advantages of honeycomb-like puckered PbTe monolayer as promising n- type thermoelectric material. Our present results would not only provide fundamental understanding of thermoelectric transport in honeycomb-like puckered PbTe monolayer, but also shed some light on the theoretical design of low dimensional PbTe-layered nanomaterials in thermoelectric applications. The honeycomb-like puckered PbTe monolayer with ultralow lattice thermal conductivity was designed for n -type thermoelectric material with excellent energy conversion efficiency. • The PbTe monolayer is direct semiconductor with wide band gaps. • The honeycomb-like puckered PbTe monolayer is dynamically and mechanically, and thermally stable. • The PbTe monolayer has low thermal conductivity, especially along armchair direction. • The puckered PbTe monolayer possesses excellent electron transport properties and power factor. • The n -type PbTe monolayer exhibit good thermoelectric properties, which can be used as potential materials for thermoelectric applications.

Development of a High Perfomance Gas Thermoelectric Generator (TEG) with Possibible Use of Waste Heat

A huge concern regarding global warming, as well as the depletion of natural fuel resources, has led to a wide search for alternative energy sources. Due to their high reliability and long operation time, thermoelectric generators are of significant interest for waste heat recovery and power generation. The main disadvantage of TEGs is the low efficiency of thermoelectric commercial modules. In this work, a unique design for a multilayer TE unicouple is suggested for an operating temperature range of 50–600 °C. Two types of thermoelectric materials were selected: «low temperature» n-and p-type TE materials (for the operating temperature range of 50–300 °C) based on Bi2Te3 compounds and «middle temperature» (for the operating temperature range of 300–600 °C) n- and p-type TE materials based on the PbTe compound. The hot extrusion technology was applied to fabricate n- and p-type low-temperature TE materials. A unique design of multilayer TEG was experienced to achieve an efficiency of up to 15%. This allows for the possibility of extracting this amount of electrical power from the heat generated for domestic and water heating.

Prediction of a high-ZT and strong anisotropic thermoelectric material: Monolayer InClSe

In this work, thermoelectric (TE) properties of monolayer InClSe are investigated by using the first-principles calculations combined with Boltzmann transport theory, which is a novel member of FeOCl-type 2D materials . We find that the electronic and thermal transport parameters along x and y axis are quite different, resulting in a strong anisotropic thermoelectric performance of monolayer InClSe, which provides a possibility to design anisotropic thermoelectric device. For n-type doping, monolayer InClSe has high electrical conductivity along x-axis. Detailed calculations reveal that the high electrical conductivity is originate from the long electron relaxation time and high connectivity of electron conduction channels. The high electrical conductivity and satisfactory Seebeck coefficient result in the excellent power factor ( PF ) for monolayer InClSe . For n-type doping, the optimal PF along x-axis can reach 47.8 mW m −1 K −2 at 700 K, which is much higher than most typical thermoelectric materials . Combining excellent PF and suppressed lattice thermal conductivity , the n-type doping monolayer InClSe has high ZT values in wide temperature range (300 K–700 K) along x-axis and the maximal ZT value reaches 2.82 at 700 K. Our results demonstrate that monolayer InClSe is a promising thermoelectric candidate for energy harvesting in moderate-temperature range. The calculated figure of merit ZT of n-type monolayer InClSe at three different temperature 300 K, 500 K, and 700 K, respectively. • We demonstrate that monolayer InClSe is a promising anisotropic thermoelectric candidate. • For n-type doping, ultra-high electrical conductivity along x-axis reaches 1.82 × 10 5 S/m (300 K) at carrier concentration 1 × 10 12 cm −2 . • For n-type doping, the optimal PF along x-axis can reach 47.8 mW m −1 K −2 at 700 K, and the maximal ZT value is 2.82.

A promising thermoelectrics In4SnSe4 with a wide bandgap and cubic structure composited by layered SnSe and In4Se3

The wide-bandgap cubic-structure semiconductor In4SnSe4 can be regarded as a product of compositing two typical layered thermoelectric materials SnSe and In4Se3. Remarkably, In4SnSe4 inherited low thermal conductivity from its parent materials. To advance the potential thermoelectric property of In4SnSe4, we systematically investigated its crystal structure and the origin of the intrinsic low thermal conductivity. In4SnSe4 crystallized in a cubic phase (space group Pa3¯), with the lattice parameters of a = b = c = 12.66 Å. The anisotropy of InSe bonds in the lattice determined the complex structure of In4SnSe4 with 72 atoms in the primitive cell. More importantly, sound velocity and elastic properties unclosed the strong anharmonicity in In4SnSe4, which contributed greatly to the low thermal conductivity. With first-principles calculations, it was found that the lone-pair electrons from In+ mainly caused the anharmonicity in the lattice. Additionally, Br was proved to be an effective dopant for In4SnSe4 to improve the electrical transport properties. This work indicated that the complex wide-bandgap semiconductor In4SnSe4 with cubic phase and intrinsic low thermal conductivity was a new promising thermoelectric material with appropriate doping.

Layered thermoelectric materials: Structure, bonding, and performance mechanisms

The ever-increasing world-wide energy consumption and crisis of environmental pollution have aroused enthusiasm on developing high-efficiency and green-clean energy conversion technology. Thermoelectric materials enable an environmentally friendly conversion between heat and electricity, and therefore serve as an optimum candidate for solving the current dilemma and contribute to the carbon-neutral target. Among the thermoelectric family, layered materials have shared a great portion with impressive thermoelectric performance originating from their (quasi-)two-dimensional crystal structure with hierarchical bonding, i.e., strong intralayer and weak interlayer bonds. This structure and bonding feature is believed to be propitious to low lattice thermal conductivity, low-dimensional electrical features, and anisotropic electron and phonon transport behaviors, which offer great opportunity to disentangle the inter-coupled thermoelectric parameters. For those benefits, layered materials emerge endlessly in the field of thermoelectricity and have achieved extensive attention. In this review, we highlight the recent progress in the field of layered thermoelectric materials. The structure and bonding peculiarities of layered thermoelectric materials are outlined. Then, following the classification of single-unit, quasi-double-unit, and double-unit layered thermoelectric materials, the crystal and bonding features in some typical layered thermoelectric materials are discussed, with focus on their current research interest and progresses. The possible mechanisms behind the performance optimization will be analyzed. Finally, some personal views on the prospect of this field, including chemical bond perspective and interlayer electronic transport enhancement are also presented.

In Situ Investigation of the Phase Transition at the Surface of Thermoelectric PbTe with van der Waals Control.

The structure of thermoelectric materials largely determines the thermoelectric characteristics. Hence, a better understanding of the details of the structural transformation process/conditions can open doors for new applications. In this study, the structural transformation of PbTe (a typical thermoelectric material) is studied at the atomic scale, and both nucleation and growth are analyzed. We found that the phase transition mainly occurs at the surface of the material, and it is mainly determined by the surface energy and the degree of freedom the atoms have. After exposure to an electron beam and high temperature, high-density crystal-nuclei appear on the surface, which continue to grow into large particles. The particle formation is consistent with the known oriented-attachment growth mode. In addition, the geometric structure changes during the transformation process. The growth of nanoparticles is largely determined by the van der Waals force, due to which adjacent particles gradually move closer. During this movement, as the relative position of the particles changes, the direction of the interaction force changes too, which causes the particles to rotate by a certain angle.

Influence of structure phase transition on the thermoelectric properties of Cu2Se1-x Te x liquid-like compounds.

Copper chalcogenide Cu2(Se,Te) compounds are well known as typical p-type thermoelectric materials with a figure of merit (ZT) that can be optimized by the ratio of Se : Te. Here, by using the mechanical alloying and solid-state reaction methods, Te was substituted into Se sites within Cu2Se as the formula Cu2Se1−xTex (x = 0.1, 0.2, 0.25, and 0.3). The observed changes in structural phase, grain morphologies, and grain size were recorded by XRD and FE-SEM imaging with the appearance of the secondary phase of Cu2Te, with a Te content of x = 0.25. The layered structure morphology was observed more clearly at the high Te content. The electrical conductivity was greatly increased with enriched Te content while the maximum Seebeck coefficient was obtained in the Cu2Se0.75Te0.25 sample. Accordingly, a power factor value of up to 9.84 μW cm−1 K−2 at 773 K was achieved. The appearance of a Cu2Te phase with a Te content of 0.25 created a structural phase transition which results in a ZT value of 1.35 at 773 K in the Cu2Se0.75Te0.25 sample.

A comprehensive review on the output voltage/power of wearable thermoelectric generators concerning their geometry and thermoelectric materials

Wearable thermoelectric generators (TEGs) are considered as a promising power supply for low power wearable electronics. To obtain high thermoelectric (TE) generation, the focus should be on two main factors, including TE materials and the configurations of TE legs. Concerning these two factors, this paper provides a comprehensive review of recent studies on wearable TEGs. In general, TE materials can be classified into three categories, including inorganic, organic, and hybrid (inorganic-organic). In addition, the TE legs can be prepared in three different configurations, including ingot-shaped, film-shaped, and yarn-shaped. Based on the reviewed literatures, the superior output powers of all the three configurations were achieved by the inorganic, hybrid, and organic TE materials, respectively. It should be noted that the ingot- and the yarn-shaped legs were mostly composed of the inorganic and the organic TE materials, respectively. Whereas, all the three types of TE materials were almost equally used to prepare the film-shaped legs. Regarding power density, the ingot-shaped legs stood first followed by the film- and the yarn-shaped legs, respectively. Precisely, the output powers of the ingot- and the film-shaped legs were at µW/cm 2 level, dropping to nW/cm 2 for the yarn-shaped legs. • Fully coating the thermoelectric legs with a stretchable elastomer reduces the output power. • Varying the boundary condition along the legs was considered to solve this problem. • The covering region of the substrate and its thermal conductivity were manipulated. • A nonhomogeneous boundary condition along the legs showed superior output power than a homogeneous one. • The results provide a clear insight into the importance of the boundary condition along the thermoelectric legs.

Realizing Cd and Ag codoping in p-type Mg3Sb2 toward high thermoelectric performance

Mg3Sb2 has attracted intensive attention as a typical Zintl-type thermoelectric material. Despite the exceptional thermoelectric performance in n-type Mg3Sb2, the dimensionless figure of merit (zT) of p-type Mg3Sb2 remains lower than 1, which is mainly attributed to its inferior electrical properties. Herein, we synergistically optimize the thermoelectric properties of p-type Mg3Sb2 materials via codoping of Cd and Ag, which were synthesized by high-energy ball milling combined with hot pressing. It is found that Cd doping not only increases the carrier mobility of p-type Mg3Sb2, but also diminishes its thermal conductivity (κtot), with Mg2.85Cd0.5Sb2 achieving a low κtot value of ∼0.67 W m−1 K−1 at room temperature. Further Ag doping elevates the carrier concentration, so that the power factor is optimized over the entire temperature range. Eventually, a peak zT of ∼0.75 at 773 K and an excellent average zT of ∼0.41 over 300 − 773 K are obtained in Mg2.82Ag0.03Cd0.5Sb2, which are ∼240% and ∼490% higher than those of pristine Mg3.4Sb2, respectively. This study provides an effective pathway to synergistically improve the thermoelectric performance of p-type Mg3Sb2 by codoping Cd and Ag, which is beneficial to the future applications of Mg3Sb2-based thermoelectric materials.

Evaluation on the Thermoelectric Cooling Ability of PbTe

High thermoelectric cooling efficiency requires a high average ZT value, especially in a low temperature range. PbTe-based compounds are typical intermediate-temperature thermoelectric materials due to their relatively low ZT values near room temperature. Here, we attempt to enhance the average ZT value of PbTe, especially at 300–600 K, through decreasing its band gap so as to evaluate the thermoelectric cooling performance. The results show that Sn alloying in PbTe can narrow its band gap from ∼0.28 to ∼0.18 eV, which shifts its peak power factor from 673 to 523 K. Combining the enhanced power factor with the reduced lattice thermal conductivity after Sn alloying, a maximum average ZT value of ∼0.74 is obtained in n-type Pb0.785Sn0.2Sb0.015Te at 300–723 K. Finally, the thermoelectric cooling performance of a Pb0.785Sn0.2Sb0.015Te-based single leg is measured, and a cooling ΔTmax of ∼15 K is realized. These results demonstrate that, after tuning the band gap, PbTe can also exhibit promising cooling performance even though it is a typical intermediate-temperature thermoelectric material.

Investigation on Low-Temperature Thermoelectric Properties of Ag2Se Polycrystal Fabricated by Using Zone-Melting Method.

Silver selenide, Ag2Se, is a promising low-temperature thermoelectric material which can be used to harvest the low-quality waste heat for electrical power generation or cool the microelectronics. Currently, the investigation on Ag2Se and its derivatives has become a hot topic in the thermoelectric community, but the thermoelectric properties of Ag2Se below 300 K have been rarely investigated. In this study, we prepared Ag2Se by using the zone-melting method. The electrical and thermal transport properties of zone-melted Ag2Se from 5 to 380 K were systematically investigated and compared with the previously reported data of Ag2Se and other typical low-temperature thermoelectric materials, such as Mg3Bi2, Bi2Te3, and BiSb. Ag2Se shows intrinsic semiconductor features, ultrahigh carrier mobility, small density-of-state effective mass, and ultralow lattice thermal conductivity. At 300 K, the zT of zone-melted Ag2Se is 0.75. This study will shed light on the further investigation of Ag2Se.