Intrinsic Low Thermal Conductivity Research Articles

DEVELOPMENT OF HIGH-PERFORMANCE THERMOELECTRIC POLYMERS VIA DOPING OR DEDOPING ENGINEERING.

It is of great significance to develop high-performance thermoelectric (TE) materials, because they can be used to harvest waste heat into electricity and there is abundant waste heat on earth. The conventional TE materials are inorganic semimetals or semiconductors like Bi2Te3 and its derivatives. However, they have problems of high cost, scare/toxic elements, high thermal conductivity, and poor mechanical flexibility. Organic TE materials emerged as the next-generation TE materials because of their merits including solution processability, low cost, abundant element, low intrinsic thermal conductivity, and high mechanical flexibility. Organic TE materials are mainly conducting polymers because of their high conductivity. Both the conductivity and Seebeck coefficient depend on the doping level, and they are interdependent. Hence, the TE properties of polymers can be improved through doping/dedoping engineering. There are three types of doping forms, oxidative (or reductive) doping, protonic acid doping, and charge transfer doping. Accordingly, they can be dedoped by different approaches. In this article, we review the methods to dope and dedope p-type and n-type TE polymers and the combination of doping and dedoping to optimize their TE properties. Secondary doping is also covered, since it can significantly enhance the conductivity of some TE polymers.

Thermophysical characterization and reliability analysis of binary composite nano doping on stearic acid-acetamide eutectic PCM

Organic phase change materials (PCM) have been extensively studied and employed for thermal energy storage applications, especially in the last decade. Wide range of melting temperature with high latent heat of fusion and absence of super cooling have made them highly desirable for energy storage applications, yet their intrinsic low thermal conductivity has been a major drawback in practical implementation. This study intends to address this and study the thermophysical characteristics of an organic PCM through composite nano doping. Stearic acid-acetamide eutectic PCM with a melting temperature of 65.73 °C and a latent heat of 203.72 J/g, was incorporated with a binary blend of Aluminum Oxide nanoparticles and multi-walled carbon nanotubes (MWCNT). The addition of metallic oxide and carbonaceous nanoparticles increased the melting temperature of the eutectic mixture by 2.9 °C and a highly advantageous increment in latent heat of fusion by 10% was observed, due to the improved molecular interaction introduced by the nanoparticles. Composite nano doping enhanced the thermal conductivity of the eutectic PCM by a 132.7% and also resulted in high optical absorption properties. The prepared eutectic mixtures were chemically stable and the eutectic PCM showed an improved final degradation temperature and thermal stability, with composite nano doping. Thermal reliability was analyzed through accelerated thermal cycling test and the eutectic mixtures could retain their thermal characteristics and chemical stability even after 500 thermal cycles. Composite nano doping proved to be a reliable thermophysical characteristics enhancement technique for organic eutectic PCM.

High cooling and power generation performance of α-MgAgSb with intrinsic low lattice thermal conductivity

α-MgAgSb is a promising near-room temperature thermoelectric material, characterized by its intrinsically low lattice thermal conductivity, a feature attributed to the significant atomic mass contrast and complex crystal structure. In this work, we achieved respective zTavg values of 0.58 in the temperature range of 150–300 K and 1.22 in the range of 300–550 K for α-MgAgSb, indicating exceptional potential for both cooling and power generation applications. Additionally, through the reduction of cross-sectional size, the stability of MgAgSb/Ag interface was enhanced under high temperature, which is crucial for the practical application of thermoelectric module. To verify the property of α-MgAgSb material, a 7-pair MgAgSb/Bi2Te3 module was fabricated, demonstrating a maximum cooling temperature difference ΔTmax of 60 K at hot-side temperature of 300 K and a power generation efficiency ηmax of 7.2 % with ΔT of 275 K. This work paves the way for the application of Mg-based thermoelectric materials.

Plasma sprayed K2Ti6O13 as thermal barrier coatings with high thermal swing for diesel piston enabled by inter-splat bonding and porosity tailoring

Thermal swing coatings with high thermal diffusivity but low thermal conductivity could increase the efficiency of diesel engines by minimizing the piston surface thermal gradient. However, the thermal diffusivity is usually positively related to the thermal conductivity and thus it is generally difficult to deposit thermal barrier coating with a low thermal conductivity but high thermal diffusivity by plasma spraying. In the present work, K2Ti6O13 with intrinsic low thermal conductivity and low melting point (1350 °C) was used as the coating material to prepare a coating with a high ratio of thermal diffusivity to thermal conductivity. Results revealed that due to the low melting point feature of K2Ti6O13 all plasma sprayed coatings have high inter-splat bonding quality which resulted in a high thermal diffusivity close to the sintered counterpart. K2Ti6O13 coatings of high porosity were plasma sprayed by optimizing powder structure, which leads to a low thermal conductivity but influences little the thermal diffusivity. It is also found that the preferential evaporation of potassium oxide from the K2Ti6O13 molten droplets leads to the formation of the TiO2 phase and generates global pores in the coating. At optimized spray conditions by using sintered porous powder, the K2Ti6O13 coating with a porosity of 21 % and single K2Ti6O13 phase reveals the lowest thermal conductivity of 0.85 W/m·K and a high diffusivity of 0.43 mm2/s. The coating exhibits the highest thermal swing of about 91 °C, having much higher performance than the conventional thermal barrier coatings used for enhancing the thermal swing effect.

Achieving High Thermoelectric Performance in ZnSe-Doped CuGaTe2 by Optimizing the Carrier Concentration and Reducing Thermal Conductivity.

The CuGaTe2 thermoelectric material has garnered widespread attention as an inexpensive and nontoxic material for mid-temperature thermoelectric applications. However, its development has been hindered by its low intrinsic carrier concentration and high thermal conductivity. This study investigates the band structure and thermoelectric properties of (CuGaTe2)1-x (ZnSe)x (x = 0, 0.25%, 0.5%, 1%, 1.5%, and 2%). The research revealed that the incorporation of Zn and Se atoms enhanced the level of band degeneracy and electron density of states near Fermi level, significantly raising carrier concentration through the formation of point defects. Simultaneously, when the doping content reached 1.5%, the ZnTe second phase emerged, collaborating with point defects and high-density dislocations, effectively scattering phonons and substantially reducing lattice thermal conductivity. Therefore, introducing ZnSe can simultaneously optimize the material's electrical and thermal transport properties. The (CuGaTe2)0.985(ZnSe)0.015 sample reaches peak ZT of 1.32 at 823 K, representing a 159% increase compared to pure CuGaTe2.

Boosting Thermoelectric Performance of PbBi2 Te4 via Reduced Carrier Scattering and Intensified Phonon Scattering.

Materials with low intrinsic lattice thermal conductivity are crucial in the pursuit of high-performance thermoelectric (TE) materials. Here, the TE properties of PbBi2 Te4-x Sex (0 ≤ x ≤ 0.6) samples are systematically investigated for the first time. Doping with Se in PbBi2 Te4 can simultaneously reduce carrier concentration and increase carrier mobility. The Seebeck coefficient is significantly increased by doping with Se, based on the density functional theory calculation, it is shown to be due to the increased bandgap and electronic density of states. In addition, the lattice strain is enhanced due to the difference in the size of Se and Te atoms, and the multidimensional defects formed by Se doping, such as vacancies, dislocations, and grain boundaries, enhance the phonon scattering and reduce the lattice thermal conductivity by about 37%. Finally, by using Se doping to reduce carrier concentration and thermal conductivity, a large ZTmax = 0.56 (at 574K) is achieved for PbBi2 Te3.5 Se0.5 , which is around 64% larger than those of the PbBi2 Te4 pristine sample. This work not only demonstrates that PbBi2 Te4 is a potential medium temperature thermoelectric material, but also provides a reference for enhancing thermoelectric properties through defect and energy band engineering.

High thermoelectric properties in polycrystalline SnSe materials realized by rare earth halide Co-doping

SnSe materials have garnered significant interest due to the intrinsic low thermal conductivity. However, its limited electrical conductivity hinders their practical implementation. This study achieved a high ZT value of 1.40 at 773 K in the samples of n-type polycrystalline SnSe0.95 + x wt% SmCl3 + y wt% ErCl3 (x = 0, 0.75, 1.0, 1.25, and 1.5; y = 0, 0.0675, 0.125, and 0.25) since (SmCl3, ErCl3) co-doping decoupled the electrical-thermal transport properties. First, the released electron carrier concentration due to SmCl3 doping enhanced the electrical transport properties. The SnSe0.95 + 1.25 wt% SmCl3 sample exhibited a high power factor of 563 μWm−1K−2 at 773 K. Then, the lattice thermal conductivity markedly decreased with further ErCl3 doping due to the high-density dislocations and coherent boundary, resulting in effective the phonon scattering. Additionally, the special microtopography was conducive to the decreased lattice thermal conductivity. Therefore, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample achieved a low lattice thermal conductivity value of 0.28 Wm−1K−1 at 773 K. Simultaneously, the (SmCl3, ErCl3) co-doped samples maintained the electrical transport properties than the SmCl3-doped samples. Consequently, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample obtained a peak ZT value of 1.40 at 773 K and a competitive average ZT value of 0.37 from 323 to 773 K, and a theoretically calculated conversion efficiency reached 7.2%, which can be applied in the deep space for power generation. This strategy can be utilized to optimize the thermoelectric performance of other thermoelectrical material systems.

Ultralow Thermal Conductivity of a Chalcogenide System Pt3Bi4Q9 (Q = S, Se) Driven by the Hierarchy of Rigid [Pt6Q12]12- Clusters Embedded in Soft Bi-Q Sublattice.

Knowledge of structure-property relationships in solids with intrinsic low thermal conductivity is crucial for fields such as thermoelectrics, thermal barrier coatings, and refractories. Herein, we propose a new "rigidness in softness" structural scheme for intrinsic low lattice thermal conductivity (κL), which embeds rigid clusters into the soft matrix to induce large lattice anharmonicity, and accordingly discover a new series of chalcogenides Pt3Bi4Q9 (Q = S, Se). Pt3Bi4S9-xSex (x = 3, 6) achieved an intrinsic ultralow κL down to 0.39 W/(m K) at 773 K, which is considerably low among the Bi chalcogenide thermoelectric materials. Pt3Bi4Q9 contains the rigid cubic [Pt6Q12]12- clusters embedded in the soft Bi-Q sublattice, involving multiple bonding interactions and vibration hierarchy. The hierarchical structure yields a large lattice anharmonicity with high Grüneisen parameters (γ) 1.97 of Pt3Bi4Q9, as verified by the effective scatter of low-lying optical phonons toward heat-carrying acoustic phonons. Consequently, the rigid-soft coupling significantly inhibits heat propagation, exhibiting low acoustic phonon frequencies (∼25 cm-1) and Debye temperatures (ΘD = 170.4 K) in Pt3Bi4Se9. Owing to the suppressed κL and considerable power factor (PF), the ZT value of Pt3Bi4S6Se3 can reach 0.56 at 773 K without heavy carrier doping, which is competitive among the pristine Bi chalcogenides. Theoretical calculations predicted a large potential for performance improvement via proper doping, indicating the great potential of this structure type for promising thermoelectric materials.

Enhancement of thermoelectric performance of Cu2MnSnSe4 alloys by regulation of lattice strain

Quaternary Cu2MnSnSe4 alloys with low intrinsic thermal conductivity are identified as promising middle-temperature thermoelectric materials. However, zT is depressed by the poor electrical performance. To overcome this issue, here, a series of Cu2.1Mn0.9SnSe4 samples are prepared by ball-milling method which appears as a time-saving technique and lattice strain variation is observed by changing the annealing time (x = 0, 1, 2, 3, 4 days). The vacancy defects concentration of Cu, with lowest vacancy defects formation energy, is changed with the competition between compression and tension-strain state, consistent with the first principles calculations, which optimizes the carrier transport. As a result, about 4 times increment of the carrier mobility is found. Moreover, the lattice strain of several nanometers is observed with TEM analysis, which scatters phonon strongly. A lowest κL value of 0.57 W m−1 K−1 at 673 K is obtained for x = 3 sample, which is close to the amorphous limit. The interactive effect of enhanced mobility and strong scattering of phonons, contributing to a record zT ∼ 0.48 at 673 K for x = 3 sample. Lattice strain engineering is an effective tactic to simultaneously optimize the electrical and thermal transport.

Phonon transport properties of Janus Pb2 XAs (X = P, Sb, and Bi) monolayers: A DFT study

Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials. In this paper, we present a first-principles calculations of the phonon transport properties of Janus Pb2PAs and Pb2SbAs monolayers. Both materials possess low lattice thermal conductivity, at least two orders of magnitude lower than graphene and h-BN. The room temperature thermal conductivity of Pb2SbAs (0.91 W/mK) is only a quarter of that of Pb2PAs (3.88 W/mK). We analyze in depth the bonding, lattice dynamics, and phonon mode level information of these materials. Ultimately, it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures. Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb2PAs and Pb2SbAs, and the three-phonon scattering is sufficient to describe their anharmonicity. In this study, the thermal transport properties of Janus Pb2PAs and Pb2SbAs monolayers are illuminated based on fundamental physical mechanisms, and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.

Promising thermoelectric performance in p-type AgBiSe2 doping with alkaline-earth metals

P-type AgBiSe2 is a promising thermoelectric material because of its intrinsic low lattice thermal conductivity and multiple valence band behavior. However, realizing high performance in p-type AgBiSe2 is challenging due to the doping bottleneck. In this work, the enhancement of thermoelectric performance for p-type AgBiSe2 has been successfully realized by adding an excess amount of Se and doping with alkaline-earth metals. We show that Ca or Mg doping at the Bi site effectively increases the room-temperature hole concentration and improves the electrical transport properties of p-type AgBiSe2. Combined with the intrinsic lower thermal conductivity, the maximum zT values of ∼0.74 and ∼0.63 at 448 K were achieved in AgBi0.98Ca0.02Se2 and AgBi0.98Mg0.02Se2, respectively. This work demonstrates a crucial strategy for improving the thermoelectric properties of p-type AgBiSe2-based materials.

Enhanced thermal conductivity and electrical insulation by patterned self-assembly of electrospun nanofibers

Low intrinsic thermal conductivity (TC) of polymer materials has severely limited their further applicability in electronic and electrical products. To enhance the TC, a strategy for constructing nanofiller-based thermal conductive networks by patterned self-assembly of electrospun nanofibers was first proposed in this paper. By selecting a regular metal mesh as the collector, the electrostatic field-induced directional deposition of nanofibers was achieved, thereby constructing interconnected heat transfer paths aligned in at least four directions. The in-plane TC of heat-pressed electrospun polyvinylidene fluoride (PVDF) nanofibers with 20 wt% loading of boron nitride nanosheets (BNNSs) can reach 7.27 W/(m·K). Electrical insulation of the PVDF/BNNS composites has also been confirmed, showing high volume resistivity and breakdown strength, which have increased by 460.0 % and 26.6 %, respectively, compared to pure PVDF. Finally, a double-layer composite film with waterproof and easy-cleaning characteristics was prepared for electronic device packaging. This simple and efficient preparation strategy for thermal conductive networks may bring new perspectives to thermal management applications.

Low dielectric constant and highly intrinsic thermal conductivity fluorine‐containing epoxy resins with ordered liquid crystal structures

AbstractEpoxy resins with a high dielectric constant and low intrinsic thermal conductivity coefficient cannot meet the current application requirements of advanced electronic and electrical equipment. Therefore, novel fluorine‐containing liquid crystal epoxy compounds (TFSAEy) with fluorinated groups, biphenyl units, and flexible alkyl chains are first synthesized via amidation and esterification reactions. Then, 4,4′‐diaminodiphenylmethane (DDM) is used as a curing agent to prepare the corresponding fluorine‐containing liquid crystal epoxy resins. The obtained dielectric constant (ε) and dielectric loss (tan δ) values of TFSAEy/DDM at 1 MHz are 2.54 and 0.025, respectively, which are significantly lower than those of conventional epoxy resins (E‐51/DDM, 3.52 and 0.038). Additionally, the intrinsic thermal conductivity coefficient (λ) of TFSAEy/DDM is 0.36 W/(m·K), 71.4% higher than that of E‐51/DDM (0.21 W/(m·K)). Meanwhile, the corresponding elastic modulus, hardness, glass transition temperature, and heat resistance index of TFSAEy/DDM are 5.73 GPa, 0.35 GPa, 213.5°C, and 188.7°C, respectively, all superior to those of E‐51/DDM (3.68 GPa, 0.27 GPa, 107.2°C, and 174.8°C), presenting potential application in high‐heating electronic component packaging and printed circuit boards.

High thermal conductivity in three-dimensional BN/epoxy composites by engineered favorable interfacial adhesion between BN sheets

Because of their excellent insulation performance and processing properties, polymers are widely used in electrical and electronic applications. However, their further applications are severely constrained by their extremely low intrinsic thermal conductivity. Boron nitride (BN), which has high thermal conductivity and ideal insulation properties, is commonly used as a filler for improving the thermal conductivity of polymers. However, the high chemical inertia of the surface of BN makes it difficult to achieve an interconnection of BN sheets when building a three-dimensional (3D) BN skeleton in a polymer. In this study, urea melt pore preparation (UMPP) was used to fabricate a 3D BN skeleton. Urea was infiltrated into the BN skeleton to minimize the interfacial thermal resistance among the BN flakes and to join BNs. When the volume of a BN is 10 %, the thermal conductivity of the BN/epoxy composites is 3.15 W/(m·K). When the BN volume is 80 %, the thermal conductivity of BN/epoxy can reach 13.65 W/(m·K), which is 6500 % of pure epoxy resin. Additionally, the skeleton exhibits a remarkable mechanical strength capable of supporting weights up to 50,000 times its own, which facilitates easier handling and operation. The electrical resistivity volume of the UMPP composite is as high as that of the pure epoxy, whereas the dielectric loss is lower than that of pure epoxy. This study provides a new method for reducing internal interface thermal resistance of a skeleton formed by thermal conductive fillers with high chemical inertia such as boron nitride.

Great Enhancement in the Seebeck Coefficient of PEDOT:PSS by Polaron Level Splitting via π–π Overlapping with Nonpolar Small Aromatic Molecules

AbstractOrganic thermoelectric (TE) materials are regarded as the next‐generation TE materials because of their merits including low cost, high mechanical flexibility, and low intrinsic thermal conductivity. However, their Seebeck coefficient is usually quite low. Herein, a new strategy is demonstrated to greatly enhance the Seebeck coefficient of poly(3,4‐ethylenedioxy‐thiophene):poly(styrenesulfonate) (PEDOT:PSS), which is the most popular TE polymer, through polaron level splitting via π–π overlapping with nonpolar small aromatic molecules including anthracene, naphthalene, and pyrene. Although these aromatic molecules are neither oxidizing nor reducing agent, they can greatly enhance the Seebeck coefficient of PEDOT:PSS films pre‐treated with dimethyl sulfoxide, acid, or acid then base, while they do not lower the electrical conductivity too much. Through such a treatment with anthracene, the Seebeck coefficient can be up to 45.5 µV K−1, and the ZT value can be up to 0.27. The enhancement is ascribed to the splitting of the lower polaron energy level of PEDOT, which is induced by the π–π overlapping between the aromatic compounds and conjugated PEDOT. This can shift up the Fermi level, thereby enhancing the Seebeck coefficient.

Impact of mobility and effective mass on the thermoelectric performance of Ni doped Cu2Se

Cu2Se, a liquid-like thermoelectric material, has shown tremendous promise in recent years due to its strong electrical properties and intrinsic low thermal conductivity, which might be optimized for future applications by engineering the performance of Cu ions. In the present study, the thermoelectric features of hydrothermally grown Cu2Se are modified by tuning the presence of nickel in the crystalline matrix. The approach of modifying electronic band structures has been explored to optimize carrier transports by balancing the competitive relationship between carrier mobility and effective mass in order to discover improvements in thermoelectric materials beyond nanostructures. Its exceptional thermoelectric performance stems from ultrahigh carrier mobility over the whole working temperature range, which is achieved by effectively modifying the transport parameters through Ni doping. The inclusion of nickel in the Cu2Se lattice at either substitutional or interstitial sites has a substantial influence on its thermal and electrical transport properties. A band sharpening caused by the presence of Ni in the lattice of Cu2Se tailored the carrier's effective mass, resulting in increased carrier mobility without compromising the carrier concentration. A simultaneous enhancement in the carrier concentration and carrier mobility is achieved due to the presence of Ni in the interstitial sites. A maximum power factor of 614 µW/mK2 is observed for the sample doped at 1.5 wt% Ni at 573 K. The lattice distortion and point defects caused by Ni substitution generated additional phonon scattering centers, resulting in a substantial decrease in thermal conductivity. The sample doped with 2 wt% Ni shows a maximum ZT value of 0.535 at 573 K, which is around 3 times higher than that of pristine Cu2Se. These findings show that nickel is a novel efficient dopant that may significantly increase the thermoelectric performance of Cu2Se via defect and band engineering.

Isovalent co-alloying contributes to considerable improvement in thermoelectric performance of BiSe bulks with weak anisotropy

BiSe with intrinsic low thermal conductivity has considered as a promising thermoelectric (TE) material at nearly room temperature. To improve its low thermoelectric figure of merit (zT), in this work, Sb and Te isovalent co-alloying was performed and significantly optimized its TE property with weakly anisotropic characteristic. After substituting Sb on Bi sites, the carrier concentration is suppressed by introduction of Sb Se site defects, which contributes to the increased absolute value of Seebeck coefficient (|S|). Further co-alloying Te on Se of the optimized composition Bi0.7Sb0.3Se, the carrier concentration increased without affecting the |S| due to the enhanced effective mass, which leads to a highest power factor of 12.8 μW/(cm·K2) at 423 K. As a result, a maximum zT of ∼0.54 is achieved for Bi0.7Sb0.3Se0.7Te0.3 along the pressing direction and the average zT (zTave) (from 300 K to 623 K) are drastically improved from 0.24 for pristine BiSe sample to 0.45. Moreover, an energy conversion efficiency ∼4.0% is achieved for a single leg TE device of Bi0.7Sb0.3Se0.7Te0.3when applied the temperature difference of 339 K, indicating the potential TE application.

High thermoelectric properties realized in polycrystalline (Ag, Ga) Co-doped SnSe via two-steps point defects modulation

Tin selenide materials have attracted much attention due to the intrinsic low thermal conductivity. However, the further application of SnSe materials is limited due to the poor electrical conductivity. Herein, a two-step doping process is employed on p-type polycrystalline SnSe materials to enhance the thermoelectric properties. It is found that the Sn0·98Ag0.01Ga0.01Se sample achieves a high ZT value of 1.53 at 823 K and a quite competitive ZTave value of 1.04 from 673 to 823 K. This is attributed to the associations of point defects, AgSn′, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. In those defects, AgSn′ acts as an accepter, which can conduce to enhancing the hole carrier concentration. Ga element doping astonishingly play dual-roles, in that it both faultlessly maintains the electrical transport properties and effectively decreases the thermal conductivity through the associations with the point defects, GaSn·, and Ga0, and nano-precipitates, SnGa4Se7, Ag9GaSe6 and AgGa1+δ. The method paves the way for achieving high thermoelectric properties in SnSe materials by the point defects engineering and nano-precipitates.

N-Type Thermoelectric AgBiPbS3 with Nanoprecipitates and Low Thermal Conductivity.

Thermoelectric sulfide materials are of particular interest due to the earth-abundant and cost-effective nature of sulfur. Here, we report a new n-type degenerate semiconductor sulfide, AgBiPbS3, which adopts a Fm3̅m structure with a narrow band gap of ∼0.32 eV. Despite the homogeneous distribution of elements at the scale of micrometer, Ag2S nanoprecipitates with dimensions of several nanometers were detected throughout the matrix. AgBiPbS3 exhibits a low room-temperature lattice thermal conductivity of 0.88 W m-1 K-1, owing to the intrinsic low lattice thermal conductivity of Ag2S and the effective scattering of phonons at nanoprecipitate boundaries. Moreover, compared to AgBiS2, AgBiPbS3 demonstrates a significantly improved weighted mobility of >16 cm2 V-1 s-1 at 300 K, leading to an enhanced PF of 1.6 μW cm-1 K-2 at 300 K. The superior electrical transport in AgBiPbS3 can be attributed to the high valley degeneracy of the L point (the conduction band minimum), which is contributed by the Pb s and Pb p orbitals. Further, Ga doping is found to be effective in modulating the Fermi levels of AgBiPbS3, leading to further enhancement of PF with a PFave of 2.7 μW cm-1 K-2 in the temperature range of 300-823 K. Consequently, a relatively high ZTave of 0.22 and a peak ZT of ∼0.4 at 823 K have been achieved in 3% Ga-doped AgBiPbS3, highlighting the potential of AgBiPbS3 as an n-type thermoelectric sulfide.

Realizing high thermoelectric performance in CeCl3-doped n-type SnSe polycrystals

SnSe is a promising thermoelectric material because of its intrinsic low lattice thermal conductivity. However, the inferior electrical transport properties restrict the thermoelectric performance of n-type SnSe polycrystals especially at lower temperature range. In this work, an effective strategy to enhance the performance of n-type SnSe polycrystals by CeCl3 doping is reported. CeCl3 doping increased both the carrier concentration and electrical conductivity. The high weighted mobility contributed to the high power factor over the whole temperature range. Combined with the reduced thermal conductivity, a peak zT of ∼1.3 at 823 K was obtained in SnSe0.92+1 mol% CeCl3 with an average zT of ∼0.36 in the temperature range of 300–773 K. This work suggests that CeCl3 doping is an effective way to optimize the thermoelectric properties of n-type SnSe polycrystals.