Active control of heat flow is crucial for managing thermal energy in sustainable technologies. However, current technologies are limited by the small switching ratio and narrow operating temperature range of thermal switching materials. Herein, we demonstrate that molybdenum disulfide (MoS2) exhibits an excellent thermal switching performance across an ultra-wide temperature range of 300-1573 K, based on a reversible transition between the non-polarized hexagonal (2H) and electronically polarized rhombohedral (3R) phases. This phase transition is kinetically limited, and the presence of electric field lowers the transition barrier, dramatically reducing the temperature and pressure required to drive the phase transition. The application of the electric field results in a vertical flip from the out-of-plane alignment along the pressure direction in the 2H phase ("off" state) to an in-plane polarization alignment along the electric field direction in the 3R phase ("on" state). This phase transition and polarized orientation switching, in conjunction with the significant anisotropic thermal transport properties of both phases, lead to a record-high thermal switching ratio of 15.2 at 300 K and maintains 6.6 at 1573 K. Our findings provide a new avenue for exploring high-performance thermal switch material triggered by phase transition and orientation changes in highly anisotropic materials.

Copper vacancies (VCu) are crucial for optimizing the thermoelectric performance of CuInTe2-based compounds by governing the hole concentration and electrical transport. However, their limited solubility and restricted ability to suppress lattice thermal conductivity hinder further improvements. In this work, we have synthesized a series of single-phase (Cu2Te)1- x(In2Te3)x samples based on the Cu2Te-In2Te3 pseudo-binary phase diagram, which enabled the regulation of the density of VCu and InCu anti-site defects over a wide concentration range. The InCu anti-site defect disrupts the local lattice symmetry, driving cations away from the tetrahedral centers and softening the lattice, thereby reducing the room-temperature lattice thermal conductivity from 5.9 W m-1 K-1 in the intrinsic sample to 1.81 W m-1 K-1 in (Cu2Te)0.4(In2Te3)0.6. Meanwhile, the increased concentration of VCu leads to the broadening of impurity levels, raising the room-temperature carrier concentration from 1.0 × 1018 cm-3 in intrinsic CuInTe2 to 5.7 × 1019 cm-3 in (Cu2Te)0.49(In2Te3)0.51. As a result of the synergistic optimization of electrical and thermal transport properties, the (Cu2Te)0.49(In2Te3)0.51 sample achieved a maximum zT of 1.21 at 873 K. This work demonstrates that pseudo-binary solid solution is an effective approach to improving the electrical and thermal properties of chalcopyrite compounds, providing a new pathway for achieving higher thermoelectric performance.

The preparation technology of powder metallurgy is an important way to prepare Bi2Te3-based bulk materials with excellent mechanical properties and thermoelectric properties. However, the loss of sample orientation during the preparation of powder metallurgy results in low thermoelectric properties of the materials. The development of high-performance Bi2Te3-based thermoelectric materials with strong plate texture and fine grains is the focus of research on high-performance Bi2Te3-based thermoelectric materials. In this paper, a series of p-type Bi2Te3-based materials were prepared by vertical corner extrusion preparation technology. The influence of extrusion temperature on the microstructure and texture characteristics of the material and its influence on the thermoelectric properties of the material were systematically studied. During the vertical corner extrusion process, the grain preferentially grows along the minimum resistance direction in the direction perpendicular to the pressure, that is, along the extrusion direction, so that the (00l) texture of the original hot-pressed sample is further enhanced; while in the direction parallel to the pressure, due to the existence of friction with the inner wall of the die during the extrusion process, this frictional resistance will promote the inversion of the grain, so that the grain is arranged in a directional manner to achieve the effect of reducing the frictional resistance, thus forming the (110) texture that is not in the original hot-pressed sample in the extruded sample, and finally completing the surface weaving from the hot-pressed sample The transition of the structure to the plate texture of the extruded sample. When the extrusion temperature is low, the atomic diffusion rate is low, which limits the dynamic recrystallization of the grain, the grain growth process and the grain deflection speed. With the increase of the extrusion temperature, these processes can be carried out rapidly, so a more obvious plate texture characteristic is formed.The 773 K extruded sample achieved high orientation factors of F(00l) = 0.51 and F(110) = 0.30 in the direction perpendicular to the pressure and parallel to the pressure, respectively, and the carrier mobility was as high as 345.4 cm2·V-1·s-1 at room temperature, which was comparable to the zone melt sample and showed excellent electrical transport performance. The power factor reached 4.43 mW·m-1·K-2 at room temperature. At the same time, the sum of lattice thermal conductivity and bipolar thermal conductivity of the 773 K extruded sample decreased to a minimum value of 0.78 W·m-1·K-1 at 323 K. Finally, the 773 K extruded sample obtained a maximum ZT value of 1.13 at 323 K, which was nearly 70 % higher than that of the hot-pressed sample. This research provides a new way for the preparation of high-performance strong plate textures and fine-grained Bi2Te3-based thermoelectric materials, and lays an important foundation for the fabrication of micro thermoelectric devices.

So far, the influence of Anderson localization on the thermoelectric performance of materials has been somewhat ambiguous. Herein, we establish that doping with Mn significantly weakens the Anderson localization in AgSbSe2. The temperature dependent electronic transport properties of Mn-doped AgSbSe2 compounds document an Anderson localization-delocalization transition that is revealed by three distinct stages: variable-range hopping conduction, nearest-neighbor hopping conduction, and band conduction. Doping AgSbSe2 compounds with Mn reduces the electronic localization barrier and shifts electron localization to a lower temperature range. Such mitigation of the Anderson localization effect greatly improves the electrical transport properties. Ultimately, the electrical conductivity was increased from 1.01 x 103 Omega-1 m-1 at room temperature for pristine AgSbSe2 to 1.28 x 104 Omega-1 m-1 for AgSb0.96Mn0.04Se2. Consequently, the power factor was improved from 0.11 mW m-1 K-2 to 0.52 mW m-1 K-2, which corresponds to a fivefold increase compared to pristine AgSbSe2. In conjunction with the intrinsically low lattice thermal conductivity of AgSbSe2, the AgSb0.98Mn0.02Se2 sample reaches the highest zT value of 1.1 at 690 K, which is more than a threefold increase in comparison with that of pristine AgSbSe2. This work demonstrates that effective modulation of the Anderson localization can be an effective approach to improve the thermoelectric performance of materials.

The preparation technology of powder metallurgy is an important way to prepare Bi2Te3-based bulk materials with excellent mechanical properties and thermoelectric properties. However, the loss of sample orientation during the preparation of powder metallurgy results in low thermoelectric properties of the materials. The development of high-performance Bi2Te3-based thermoelectric materials with strong plate texture and fine grains is the focus of research on high-performance Bi2Te3-based thermoelectric materials. In this paper, a series of p-type Bi2Te3-based materials is prepared by vertical corner extrusion preparation technology. The influences of extrusion temperature on the microstructure and texture characteristics of the material and its influence on the thermoelectric properties of the material are systematically studied. In the vertical corner extrusion process, grains preferentially grow along the minimum resistance direction perpendicular to the pressure, that is, along the extrusion direction, thereby further enhancing the (00l) texture of the original hot-pressed sample; in the direction parallel to the pressure, due to friction with the inner wall of the die in the extrusion process, this frictional resistance will promote the inversion of the grains, so that the grains are arranged in a directional manner to reduce the frictional resistance, thus forming the (110) texture, which is not present in the original hot-pressed sample, in the extruded sample, and finally completing the transition from the hot-pressed sample to the plate texture of the extruded sample. When the extrusion temperature is low, the atomic diffusion rate is low, which limits the dynamic recrystallization of the grain, the grain growth process, and the grain deflection speed. With the increase of the extrusion temperature, these processes can be carried out rapidly, thus forming a more obvious plate texture characteristic. The 773 K extruded sample achieves high orientation factors of F-(00l) = 0.51 and F-(110) = 0.30 in the directions perpendicular to the pressure and parallel to the pressure, respectively, and the carrier mobility is as high as 345.4 cm(2)V-1s(-1) at room temperature, which is comparable to the carrier mobility of the zone melt sample, showing excellent electrical transport performance. The power factor reaches 4.43 mWm(-1)K-2 at room temperature. At the same time, the sum of lattice thermal conductivity and bipolar thermal conductivity of the 773 K extruded sample decreases to a minimum value of 0.78 Wm(-1)K-1 at 323 K. Finally, the 773 K extruded sample obtains a maximum ZT value of 1.13 at 323 K, which is nearly 70% higher than that of the hot-pressed sample. This research provides a new way for preparing high-performance strong plate textures and fine-grained Bi2Te3-based thermoelectric materials, and lays an important foundation for fabricating micro thermoelectric devices.

Zone melting technique is an important method for commercial preparation of Bi2Te3-based thermoelectric materials. The zone melting purification process is affected by segregation of materials. However, so far, the effect of zone melting process on the segregation mechanism of Bi2Te3-based materials has not yet formed unified understanding. In particular, increase of material components significantly affects the segregation process and uniformity. In this study, n-type Bi(1.9)6Sb(0.04)Te(2.70)Se(0.30)Br(0.006 )material was used as the research object, and the melting-zone melting-annealing process was used to systematically explore the influence of zone melting temperature on the composition and uniformity of thermoelectric performance. It was found that the zone melting temperature had a great influence on uniformity of the ingot, and the axial composition segregation was an important factor affecting its uniformity. At high zone melting temperature (>= 988 K), the segregation of Bi2Te3-rich phase appeared at the top of the ingot, which made the poor uniformity of thermoelectric properties of the material. The maximum difference of ZT at room temperature in different regions (center top, edge top (ET), center bottom, edge bottom) of samples with zone melting temperatures of 988 and 1003 K reached 31.5% and 28.6%, respectively. Reducing the zone melting temperature to 958 K significantly inhibited the segregation of Bi2Te3-enriched phase, and a cylindrical ingot (inner diameter of 16 mm, height of 55 mm) with excellent thermoelectric properties and uniformity was prepared. The maximum difference of ZT at room temperature in different regions was only 14%, and the maximum ZT of 958 K-ET sample was 1.05 at 350 K. This study reveals the regulation mechanism of zone melting temperature on the composition and thermoelectric performance uniformity of multi-component n-type (Bi, Sb)(2)(Te, Se)(3)-based materials, which provides important guidance for the preparation of high-performance thermoelectric materials with excellent uniformity.

The explosive growth of artificial intelligence, big data, and the Internet of Things is driving an unprecedented demand for computing power and energy efficiency. However, conventional von Neumann architectures are increasingly constrained by the physical and economic limits of transistor scaling in the post-Moore era. Ferroelectric transistors (FeFETs) are far more than a novel memory technology and instead represent a revolutionary platform that seamlessly integrates nonvolatile storage, in-memory computation, and multi-modal sensing into a single, energy-efficient device, overcoming the bottlenecks of traditional computing architectures. This review provides a comprehensive overview of ferroelectric materials, including perovskite oxides, hafnium-based compounds, organics, and emerging 2D systems, emphasizing their polarization original mechanisms and structureproperty relationships. This study focuses on the device physics and engineering of three terminal FeFETs, with particular attention to the current issues, optimization strategies, and contrasting operation principles of ferroelectric dielectric and semiconductor-based designs. Finally, the expanding applications of FeFETs in nonvolatile memory, neuromorphic computing, and artificial intelligence hardware from device to system integration is discussed, and an outlook toward scalable, low-power, and multifunctional electronics driven by ferroelectric innovation is presented.

Ag2TexS1-x usually undergo various phase structures upon heating or cooling processes; however, the correlation between the heat treatment, the phase structure, and the physical properties is still a controversy. Herein, three different phases are realized for Ag2TexS1-x (0.35 ≤ x ≤ 0.65) samples during the heat treatment, including the low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase. The metastable amorphous phase is an intermediate phase formed during transition from the high-temperature cubic phase to the low-temperature crystalline phase upon cooling via a solid-state conversion rather than the conventional liquid quenching process. The relative content of these three phases is highly sensitive to the heat treatment process. This as-formed low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase convert into the low-temperature crystalline phase and high-temperature cubic phase through long-time dwelling at the temperature below or above the transition temperature around 567 K, respectively. The status of the low-temperature crystalline phase, amorphous phase, and high-temperature cubic phase significantly affects the thermoelectric properties, resulting in the thermal hysteresis of thermoelectric properties. Below the phase transition temperature (TM), the electrical conductivity of the amorphous phase surpasses that of the low-temperature crystalline phase, which shows a growth of 112% for the Ag2Te0.60S0.40 sample annealed at 823 K in comparison with that of the sample annealed at 473 K. For Ag2Te0.50S0.50 samples annealed at 473 K, the maximum ZT value reaches 1.02 at 623 K during the initial test, while the maximum ZT value is improved to 1.34 at 523 K in the second-round test.

Since the lattice thermal conductivity of thermoelectric materials is a relatively independent parameter, exploring semiconductor materials with intrinsically low lattice thermal conductivity is an important direction in the field of thermoelectric research. Herein, a high figure of merit ZT of 1.23 at 873 K and an exceptionally low lattice thermal conductivity of 0.18 W m(-1) K-1 are realized in the n-type CuIn7Se11 compound for the first time. The weak In-Se chemical bonds induce strong coupling between acoustic phonon and optical phonon with low frequency, leading to low sound velocity. The highly disordered configuration of Cu, In, and vacancies at In-2, In-3, and M sites, in conjunction with atomic-scale slips and flips intensify phonon scattering. All these result in an intrinsically low thermal conductivity of the CuIn7Se11 compound. DFT calculation reveals that the density of states at the bottom of the conduction band is mainly contributed by the coupling between 4p orbitals of Se atoms and 5s orbitals of In atoms, featuring with a small effective mass. This small effective mass of charge carrier renders the CuIn7Se11 compound high carrier mobility of 435 cm(2) V-1 s(-1) at 300 K. Consequently, the CuIn7Se11 compound possesses an extraordinary thermoelectric performance

Antimony chalcogenide solar cells have captured considerable attention in recent years with an efficiency of over 10%, due to their use of Earth-abundant materials and superior physical characteristics. Despite these achievements, significant nonradiative recombination processes within these solar cells present a substantial obstacle to further efficiency improvements. Therefore, this review delves into the primary mechanisms responsible for nonradiative recombination losses in antimony chalcogenide solar cells. Additionally, the latest advancements in addressing these losses are summarized. Finally, potential directions for future research efforts aimed at reducing nonrecombination losses and enhancing the overall performance of these devices are outlined. This review summaries the latest methods that can effectively suppress the nonradiative recombinations, including innovative synthesis method and interface engineering strategies.image (c) 2024 WILEY-VCH GmbH

Exploring the relationship between crystal structure and thermoelectric performance is a pivotal topic in the thermoelectric field. In this study, we have comprehensively investigated the correlation between the structural evolution of (GeTe)m(Sb2Te3)n pseudo-binary system and the thermoelectric properties. The proportion of van der Waals bonds increases with the rising Sb2Te3 content, resulting in an increase in the anisotropy of the electrical conductivity and a decrease in the average sound velocity. Additionally, the cation sites in the crystal lattice of these compounds exhibit a mixed occupancy of Ge/Sb atoms, although the cation sites adjacent to the van der Waals gaps are predominantly occupied by Sb atoms. The ultra-low lattice thermal conductivity of the GST124 and GST147 compounds is mainly attributed to the high concentration of van der Waals bonds and enhanced phonon scattering arising from Ge/Sb mixed cation occupancy and high density of defect structures. The high electrical conductivity combined with the low lattice thermal conductivity enables GST124 and GST147 compounds to achieve a maximum ZT value of 0.56 and 0.57, respectively. Higher thermoelectric performance can be achieved through optimization of the microstructure as well as the carrier concentration.

The stabilization at low temperatures of the Ag2S cubic phase could afford the design of high-performance thermoelectric materials with excellent mechanical behavior, enabling them to withstand prolonged vibrations and thermal stress. In this work, we show that the Ag2TexS1-x solid solutions, with Te content within the optimal range 0.20 ≤ x ≤ 0.30, maintain a stable cubic phase across a wide temperature range from 300 to 773 K, thus avoiding the detrimental phase transition from monoclinic to cubic phase observed in Ag2S. Notably, the Ag2TexS1-x (0.20 ≤ x ≤ 0.30) samples showed no fractures during bending tests and displayed superior ductility at room temperature compared to Ag2S, which fractured at a strain of 6.6%. Specifically, the Ag2Te0.20S0.80 sample demonstrated a bending average yield strength of 46.52 MPa at 673 K, significantly higher than that of Ag2S, whose bending average yield strength dropped from 80.15 MPa at 300 K to 12.66 MPa at 673 K. Furthermore, the thermoelectric performance of the Ag2TexS1-x (0.20 ≤ x ≤ 0.30) samples surpassed that of both InSe and pure Ag2S, with the Ag2Te0.30S0.70 sample achieving the highest ZT value of 0.59 at 723 K. These results indicate substantial potential for practical applications due to enhanced durability and thermoelectric performance.

Exploring the relationship between crystal structure and thermoelectric performance is a pivotal topic in the thermoelectric field. In this study, we have comprehensively investigated the correlation between the structural evolution of (GeTe) m (Sb 2 Te 3 ) n pseudo-binary system and the thermoelectric properties. The proportion of van der Waals bonds increases with the rising Sb 2 Te 3 content, resulting in an increase in the anisotropy of the electrical conductivity and a decrease in the average sound velocity. Additionally, the cation sites in the crystal lattice of these compounds exhibit a mixed occupancy of Ge/Sb atoms, although the cation sites adjacent to the van der Waals gaps are predominantly occupied by Sb atoms. The ultra-low lattice thermal conductivity of the GST124 and GST147 compounds is mainly attributed to the high concentration of van der Waals bonds and enhanced phonon scattering arising from Ge/Sb mixed cation occupancy and high density of defect structures. The high electrical conductivity combined with the low lattice thermal conductivity enables GST124 and GST147 compounds to achieve a maximum ZT value of 0.56 and 0.57, respectively. Higher thermoelectric performance can be achieved through optimization of the microstructure as well as the carrier concentration.

Grain size refinement is the vital stratagem for improving mechanical properties of Bi2Te3-based compounds. However, the donor-like effect induced by grain size refinement strongly restricts the thermoelectric properties especially in the vicinity of room temperature. Once the donor-like effect is generated, it is very difficult to remove the donor-like effect by the simple heat treatment process and other processes. In this study, the effect of particle size on the donor-like effect and thermoelectric properties was systematically studied for Bi2Te3-based compounds. As the particle size decreases, the donor-like effect is enhanced significantly. The oxygen-induced donor-like effect dramatically increases the carrier concentration from 3.36×1019 cm-3 for 10 M sintered sample to 7.33×1019 cm-3 for 120 M sintered sample, which is largely beyond the optimal carrier concentration of 2.51×1019 cm-3 and seriously deteriorates the thermoelectric performance. However, when the particle size of the powder is 1~2 mm, the Seebeck coefficient of -195 μV K-1 and the carrier concentration of 3.36×1019 cm-3 near room temperature are achieved, which are similar to the ZM sample with the Seebeck coefficient of -203 μV K-1 and the carrier concentration of 2.51×1019 cm-3. The powders without the obvious donor-like effect can be used as the excellent raw materials for powder metallurgy process. A maximum ZT value of 0.75 is achieved for the 18 M sintered sample. The excellent thermoelectric properties is expected to obtain by enhancing the texture further. This study provides an important guidance for the preparation of materials with excellent thermoelectric and mechanical properties by powder metallurgy process and provides a new path to regulate and effectively suppress the generation of donor-like effects.

Grain size refinement is the vital stratagem for improving mechanical properties of Bi2Te3-based thermoelectric material. However, the donor-like effect induced by grain size refinement seriously deteriorates the thermoelectric properties especially near room temperature. Once the donor-like effect is generated, it is very difficult to eliminate the donor-like effect by the simple heat treatment process and other processes. In this study, the influences of particle size on the donor-like effect and thermoelectric properties are systematically studied for Bi2Te3-based compounds. As the particle size decreases, the donor-like effect is enhanced significantly. The oxygen-induced donor-like effect dramatically increases the carrier concentration from 3.36x 1019 cm-3 for 10 M sintered sample to 7.33x1019 cm-3 for 120 M sintered sample, which is largely beyond the optimal carrier concentration of 2.51x1019 cm-3 and seriously deteriorates the thermoelectric properties. However, when the particle size of the powder is 1-2 mm, the Seebeck coefficient of -195 mu V/K and the carrier concentration of 3.36x1019 cm-3 near room temperature are achieved, which are similar to those of the ZM sample with the Seebeck coefficient of -203 mu V/K and the carrier concentration of 2.51x1019 cm-3. The powders without the obvious donor-like effect can be used as the excellent raw material for powder metallurgy process. A maximum ZT value of 0.75 is achieved for the 18 M sintered sample. The excellent thermoelectric properties are expected to be obtained by enhancing the texture further. This study provides a new way to regulate and effectively suppress the generation of the donor-like effect, and provides an important guidance for the preparation of materials with excellent thermoelectric and mechanical properties by powder metallurgy process.

Acrylamide (AM) generally forms in high -temperature processes and has been classified as a potential carcinogen. In this study, we put forward a maneuverable solid-state luminescence sensor using polydimethylsiloxane (PDMS) as the matrix coupled with upconversion nanoparticles as the indicator. The core -shell upconversion nanoparticles emitting cyan light were uniformly encapsulated in PDMS. Then it was further modified with complementary DNA of AM aptamer. The nanocrystalline fluorescein isothiocyanate isomer (FITC), coupled with AM aptamer, was attached to the surface of PDMS. FITC effectively quenched the upconversion luminescence through fluorescence resonance energy transfer (FRET). The introduction of AM resulted in preferentially bound to aptamer caused the separation of the quencher and the donor, and led to luminescence recovery. The developed sensor was applied for both spectral and visual monitoring, demonstrating a detection limit (LOD) of 1.00 nM and 1.07 nM, respectively. Importantly, in the actual foodstuffs detection, there is no obvious difference between the results of this study and the standard method, which indicates the developed method has good accuracy. Therefore, this solid-state sensor has the potential for on -site detection using a smartphone device and an Android application.

We have determined the complex atomic structure of high-temperature α-Ag 9 GaTe 6 phase with a hexagonal lattice ( P 6 3 mc space group, a = b =8.2766 Å, c =13.4349 Å). The structure has outer [GaTe 4 ] 5− tetrahedrons and inner [Ag 9 Te 2 ] 5+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage-like [Ag 9 Te 2 ] 5+ clusters. The highly disordered Ag ions vibrate in-harmonically, producing strong coupling between low frequency optical phonons and acoustic phonons. This in conjunction with a low sound velocity of 1354 m s −1 leads to an ultralow thermal conductivity of 0.20 W m −1  K −1 at 673 K. Meanwhile, the deficiency of Ga in Ag 9 Ga 1− x Te 6 compounds effectively optimizes the electronic transport properties. Ag 9 Ga 0.91 Te 6 attains a highest power factor of 0.40 mW m −1  K −2 at 673 K. All these contribute to a much-improved ZT value of 1.13 at 623 K for Ag 9 Ga 0.95 Te 6 , which is 41 % higher than that of the pristine Ag 9 GaTe 6 sample.

Although traditional ferroelectric materials are usually dielectric and nonconductive, GeTe is a typical ferroelectric semiconductor, possessing both ferroelectric and semiconducting properties. GeTe is also a widely studied thermoelectric material, whose performance has been optimized by doping with various elements. However, the impact of the ferroelectric domains on the thermoelectric properties remains unclear due to the difficulty to directly observe the ferroelectric domains and their evolutions under actual working conditions where the material is exposed to high temperatures and electric currents. Herein, based on in-situ investigations of the ferroelectric domains and domain walls in both pure and Sb-doped GeTe crystals, we have been able to analyze the dynamic evolution of the ferroelectric domains and domain walls, exposed to an electric field and temperature. Local structural heterogeneities and nano-sized ferroelectric domains are generated due to the interplay of the Sb3+ dopant and the Ge-vacancies, leading to the increased number of charged domain walls and a much improved thermoelectric performance. This work reveals the fundamental mechanism of ferroelectric thermoelectrics and provides insights into the decoupling of previously interdependent properties such as thermo-power and electrical conductivity.

Bi2Te3 based thermoelectric device is the only commercialized thermoelectric module. The thermal stability of the interface between the thermoelectric materials and barrier layer or electrode plays pivotal role for the stability and reliability of micro thermoelectric devices especially for power generation. In this work, the thermal stability, bonding strength and structure evolution of the interface between Bi2Te3 based materials (both n type and p type materials) and Ni barrier layer were systematically investigated. The interface between Ni and Bi2Te3 based materials demonstrates an ohmic contact with the contact resistivity of 3.64 mu Omega cm(2) and 5.31 mu Omega cm(2) for p-type and n-type element respectively. The bonding strength of p-type and n type element with electrode is 13.43 MPa and 17.62 MPa, respectively. Upon annealing at 423 K for 7 days, due to the mass diffusion between Ni and Bi2Te3 based materials, a thin Ni-Te layer is formed. With further extending the annealing time at 423 K to 42 days, the thickness of the diffusion layer increases to 3 mu m. The growth of diffusion layer enhances the bonding strength to 19.81 MPa. However, this is accompanied with a sharp increase in the contact resistivity to 14.48 mu Omega cm(2) for n-type element and to 6 mu S-2 cm(2) for p-type element with Ni barrier. The increase in the contact resistance deteriorates the output power of thermoelectric module especially for the micro-device from 2.60 mW to 2.48 mW under the temperature gradient of 20 K. This work points out that for the application of Bi2Te3 based thermoelectric device in power generation above 423 K, appropriate barrier layer is indispensable and plays significant role for the performance of the device. (C) 2021 Published by Elsevier B.V.

In this study, p-type Bi0.5Sb1.5Te3 ingots were fabricated with a wide range of carrier concentrations through zone melting method. The anisotropy of thermoelectric properties was systematically investigated. The layered structure with weak van der Waals bonding, which selectively scatters charge carrier and phonon, produces the anisotropic thermoelectric properties. The intrinsic excitation generates electron-hole pairs with highly anisotropic transport behavior, resulting in a remarkable anisotropic Seebeck coefficient and bipolar thermal conductivity. The out-of-plane Seebeck coefficient is remarkably higher than that in-plane Seebeck coefficient in the intrinsic excitation regime. Doping with Te decreases the extrinsic carrier concentration of BiSbTe alloy, strengthening the intrinsic excitation and the contribution of the bipolar thermal conductivity. Optimization of carrier concentration via adjusting Te content significantly improves the thermoelectric performance. The maximum power factor of 5.2 mW m(-1) K-2 is achieved for the Bi0.5Sb1.5Te3.08 sample at room temperature along the in-plane direction. A high ZT value of 1.06 at 375 K is attained for the Bi0.5Sb1.5Te3.04 sample along the inplane direction, while the maximum out-of-plane ZT value is achieved as much as 0.94 at 450 K for Bi0.5Sb1.5Te3.02 sample.