Thermoelectric Bi2Te3 Research Articles

Electric Field-Induced Enhanced Raman Spectroscopy Sensor and Photocatalysis with Thermoelectric-Plasmonic Metal Nanocomposites.

Electric field-induced surface-enhanced Raman scattering (E-SERS) substrates have been proven to further enhance the attained Raman intensity. Herein, integrated with plasmonic Ag nanoparticles (Ag NPs), the thermoelectric Bi2Te3 plate as an E-SERS substrate decreased the limit of detection by 2 orders of magnitude and increased the SERS signal by >20 times compared to those without electrical field induction. The thermoelectric potential produced by the Bi2Te3 plate could modulate the electron density and subsequently change the Fermi level of Ag. This increases the resonant electron transition probability using a broad range of molecules. The plasmon-activated catalytic reactions of the interconversion between p-nitrothiophenol and p,p'-dimercaptoazobenzene could be controlled through the E-SERS template. On the basis of the finite element method, explicit theoretical analysis indicated that the Ag NP-Bi2Te3-molecule charge transfer could improve our understanding of the SERS and photocatalytic mechanism.

Thermal detector based on a suspended polyimide membrane for infrared radiation applications

This Letter details a pioneering study on the design and nanofabrication process of a thermoelectric infrared radiation detector using a suspended polyimide membrane. The research includes a comprehensive analysis of thermoelectric doped Bi2Te3 thin films, comparing their expected performance regarding noise and specific detectivity with other infrared detectors, particularly those in the silicon sector. Experimental results and calculations shed light on responsivity and time constants. In the absence of absorption layers, specific detectivity values for visible and near infrared radiation are measured at 9.2 × 107 and 2.9 × 107cm Hz/W, respectively, with a time constant nearing 20 ms. Calculations show that introducing an optimized absorption layer with ε = 1 significantly improves specific detectivity, reaching 9.0 × 108cm Hz/W. Subsequent calculations also show that further enhancement can be obtained by etching the polyimide membrane to a 1-micron thickness, resulting in an exceptional specific detectivity value of 8.4 × 109cm Hz/W, placing it among the best in the current state-of-the-art.

Flexible temperature-pressure dual sensor based on 3D spiral thermoelectric Bi2Te3 films

Dual-parameter pressure-temperature sensors are widely employed in personal health monitoring and robots to detect external signals. Herein, we develop a flexible composite dual-parameter pressure-temperature sensor based on three-dimensional (3D) spiral thermoelectric Bi2Te3 films. The film has a (000l) texture and good flexibility, exhibiting a maximum Seebeck coefficient of −181 μV K–1 and piezoresistance gauge factor of approximately −9.2. The device demonstrates a record-high temperature-sensing performance with a high sensing sensitivity (−426.4 μV K−1) and rapid response time (~0.95 s), which are better than those observed in most previous studies. In addition, owing to the piezoresistive effect in the Bi2Te3 film, the 3D-spiral deviceexhibits significant pressure-response properties with a pressure-sensing sensitivity of 120 Pa–1. This innovative approach achieves high-performance dual-parameter sensing using one kind of material with high flexibility, providing insight into the design and fabrication of many applications, such as e-skin.

In Situ Synthesis of High Thermoelectric Performance Bi2Te3 Flexible Thin Films through Thermal Diffusion Engineering

Bi2Te3-based materials are promising candidates for near-room-temperature applications due to their high thermoelectric performance and low cost. Here, an innovative thermal diffusion strategy combined with magnetron sputtering and thermal evaporation methods was employed to fabricate Bi2Te3 flexible thin films (f-TFs) on a flexible polyimide substrate. An in situ synthesis of Bi2Te3 f-TFs with good crystallinity was obtained using a straightforward thermal diffusion method through diffusion of Te into a Bi precursor under low vacuum conditions (1 × 105 Pa). This method offers easy preparation, low cost, and a large-area film preparation for industrialization. The electrical conductivity increases with increasing thermal diffusion temperatures. A high room temperature carrier mobility of ~28.7 cm−2 V−1 S−1 and an electrical conductivity of ~995.6 S cm−1 can be achieved. Then, a moderate room temperature Seebeck coefficient >100 μV K−1 was obtained due to the chemical stoichiometry being close to the standard by optimizing the thermal diffusion temperature. Consequently, a maximum room temperature PF of ~11.6 μW cm−1 K−1 was observed in Bi2Te3 f-TFs prepared using a thermal diffusion temperature of 653 K. The thermal diffusion strategy applied in the thin film preparation represents an effective approach for the preparation of high thermoelectric performance Bi2Te3 f-TFs, offering a promising route for future thermoelectric applications.

Optimization and comparison of two-stage thermoelectric generators considering the influence of temperature variation on materials for waste heat utilization

Thermoelectricity technology, as a kind of cost-effective and pollution-free power generation solution, is often used for waste heat recovery and utilization. In this paper, the temperature distribution of a Two-stage Thermoelectric Generator (TTEG) under constant temperature conditions has been studied using a one-dimensional heat conduction model. Moreover, by combining the obtained temperature distribution with the three-dimensional size of TTEG, a calculation formula of resistance and voltage was developed based on the calculus method. When the sum of cross-sectional areas of all the PN-type thermoelectric arms respectively in high- and low-temperature layers is constant, the optimal ratio between cross-sectional areas of a single PN-thermoelectric arm respectively in high- and low-temperature layers can be calculated using the proposed formula in this study to achieve the maximum output power. Results also showed the relationship between the heights of PN-type thermoelectric arms and the temperature distributions in high- and low-temperature layers. Using PbTe as the medium temperature thermoelectric material and Bi2Te3 as the low temperature thermoelectric material, a case study was conducted on the PN-type thermoelectrics with the same total height and the same total cross-sectional area. The theoretical calculation results showed that the bigger of maximum output power between the two-stage thermoelectric generator and that of the Segmented Thermoelectric Generator (STEG) is related to the hot and cold end temperature.

Stacking fault-induced strengthening mechanism in thermoelectric semiconductor Bi2Te3

Stacking fault-induced strengthening mechanism in thermoelectric semiconductor Bi2Te3

Mid-infrared circular-polarization-sensitive photodetector based on a chiral metasurface with a photothermoelectric effect.

Photothermoelectric conversion in chiral metasurfaces with thermoelectric material provides an effective way to achieve circular polarization recognition. In this paper, we propose a circular-polarization-sensitive photodetector in a mid-infrared region, which is mainly composed of an asymmetric silicon grating, a film of gold (Au), and the thermoelectric B i 2 T e 3 layer. The asymmetric silicon grating with the Au layer achieves high circular dichroism absorption due to a lack of mirror symmetry, which results in a different temperature increasing on the surface of the B i 2 T e 3 layer under right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) excitation. Then the chiral Seebeck voltage and output power density are obtained, thanks to the thermoelectric effect of B i 2 T e 3. All the works are based on the finite element method, and the simulation results are conducted by the Wave Optics module of COMSOL, which is coupled with the Heat Transfer module and Thermoelectric module of COMSOL. When the incident flux is 1.0W/c m 2, the output power density under RCP (LCP) light reaches 0.96m W/c m 2 (0.01m W/c m 2) at a resonant wavelength, which achieves a high capability of detecting circular polarization. Besides, the proposed structure shows a faster response time than that of other plasmonic photodetectors. Our design provides a novel, to the best of our knowledge, method for chiral imaging, chiral molecular detection, and so on.

Selective Dissolution-Derived Nanoporous Design of Impurity-Free Bi2 Te3 Alloys with High Thermoelectric Performance.

Thermoelectric technology, which has been receiving attention as a sustainable energy source, has limited applications because of its relatively low conversion efficiency. To broaden their application scope, thermoelectric materials require a high dimensionless figure of merit (ZT). Porous structuring of a thermoelectric material is a promising approach to enhance ZT by reducing its thermal conductivity. However, nanopores do not form in thermoelectric materials in a straightforward manner; impurities are also likely to be present in thermoelectric materials. Here, a simple but effective way to synthesize impurity-free nanoporous Bi0.4 Sb1.6 Te3 via the use of nanoporous raw powder, which is scalably formed by the selective dissolution of KCl after collision between Bi0.4 Sb1.6 Te3 and KCl powders, is proposed. This approach creates abundant nanopores, which effectively scatter phonons, thereby reducing the lattice thermal conductivity by 33% from 0.55 to 0.37 W m-1 K-1 . Benefitting from the optimized porous structure, porous Bi0.4 Sb1.6 Te3 achieves a high ZT of 1.41 in the temperature range of 333-373 K, and an excellent average ZT of 1.34 over a wide temperature range of 298-473 K. This study provides a facile and scalable method for developing high thermoelectric performance Bi2 Te3 -based alloys that can be further applied to other thermoelectric materials.

Features of microstructure and thermoelectric properties of the cermet composites based on grained Bi2Te3 matrix with locally-gradient Ni@NiTe2 inclusions

Starting Bi2Te3 and Ni powders were spark-plasma-sintered (SPS) to prepare thermoelectric cermet composites consisting of thermoelectric Bi2Te3 matrix with different content, x, of ferromagnetic Ni filler (x = 0.00, 0.50, 0.85, 1.25 and 1.50 at. %). Grained Bi2Te3 matrix of composites is texturing under sintering. Texturing degree is x-dependent that is attributed to ability of Ni particles act as lubricant. New trigonal NiTe2 phase is formed under SPS-process. The Ni and NiTe2 phases correspond to filler Ni@NiTe2 (“core”-“shell”) inclusions. Forming these inclusions is originated from chemical interaction between Bi2Te3 and Ni during SPS-process. A Ni→NiTe2 reaction is accelerated with increasing x that results in growing Ni@NiTe2 inclusions and increasing fraction of shell. Thermoelectric properties of composites are x-dependent that is due to non-monotonic changes in texturing degree, size of the inclusions and concentration of majority carriers with increasing x. Thermoelectric figure-of-merit of composites is remarkably enhancing as compared to that of Bi2Te3 matrix.

Microstructure evolution during reduction and sintering of 3D-extrusion-printed Bi2O3+TeO2 inks to form Bi2Te3

As an alternative to beam-based additive manufacturing, 3D ink-extrusion additive manufacturing is studied here for thermoelectric Bi2Te3, starting from Bi2O3+TeO2 oxide precursor powders. In situ synchrotron XRD in flowing H2 at elevated temperatures reveals the complex phase evolution upon co-reduction leading to the formation of Bi2Te3, Bi2TeO5 and Bi2TeO2. Sintering trials performed using optimal temperatures identified by in situ XRD show that low heating rates and extensive holding times are required to achieve full co-reduction to pure Bi2Te3. The formation of liquid Bi at the temperatures required for oxide reduction leads to local transient-liquid-phase sintering, creating a coarse-grained porous structure. To limit the amount of free Bi, compositional homogenization prior to reduction is achieved by oxide pre-sintering in air, allowing to access the high temperatures required for interdiffusion. After co-reduction of the complex Bi2Te4O11+Bi2Te2O7+TeO2 pre-sintered ceramic, fine-grained, Te-rich n-type Bi2Te3 is obtained, achieving a zT of ∼0.4 between 373 and 423 K. The present study demonstrates the feasibility of synthesizing thermoelectrics from oxide precursors, with the potential of simplifying the processing chain and reducing cost to obtain 3D-extruded thermoelectric parts with complex shapes and architectures.

Non-universal scaling of thermoelectric efficiency in 3D and 2D thermoelectric semiconductors

We performed the first-principles calculation on common thermoelectric semiconductors Bi2Te3, Bi2Se3, SiGe, and PbTe in bulk three-dimension (3D) and two-dimension (2D). We found that miniaturisation of materials does not generally increase the thermoelectric figure of merit (ZT) according to the Hicks and Dresselhaus (HD) theory. For example, ZT values of 2D PbTe (0.32) and 2D SiGe (0.04) are smaller than their 3D counterparts (0.49 and 0.09, respectively). Meanwhile, the ZT values of 2D Bi2Te3 (0.57) and 2D Bi2Se3 (0.43) are larger than the bulks (0.54 and 0.18, respectively), which agrees with HD theory. The HD theory breakdown occurs because the band gap and band flatness of the materials change upon dimensional reduction. We found that flat bands give a larger electrical conductivity (σ) and electronic thermal conductivity (κ el) in 3D materials, and smaller values in 2D materials. In all cases, maximum ZT values increase proportionally with the band gap and saturate for the band gap above 10 k B T. The 2D Bi2Te3 and Bi2Se3 obtain a higher ZT due to the flat corrugated bands and narrow peaks in their DOS. Meanwhile, the 2D PbTe violates HD theory due to the flatter bands it exhibits, while 2D SiGe possesses a small gap Dirac-cone band.

Forming the locally-gradient Ni@NiTe2 domains from initial Ni inclusions embedded into thermoelectric Bi2Te3 matrix

Mixtures of thermoelectric Bi2Te3 powder and ferromagnetic Ni powder were spark-plasma-sintered to prepare bulk composites with different Ni content (0.00, 0.50, 0.85, 1.25 and 1.50 at.%). Hexagonal Bi2Te3, cubic Ni and trigonal NiTe2 phases coexist in the composites. Bi2Te3 phase forms matrix of the composite, whereas Ni and NiTe2 phases correspond to filler. The filler is formed by locally-gradient Ni@NiTe2 (“core–shell”) inclusions. Forming the “core–shell” inclusions is due to high-temperature diffusion redistribution of matrix and filler atoms during the composites sintering. The thermoelectric figure-of-merit of the composites with the locally-gradient inclusions is remarkably enhanced as compared to that of the Bi2Te3 matrix.

Heavy Chalcogenide-Based Ionic Liquids in Syntheses of Metal Chalcogenide Materials near Room Temperature.

This minireview describes two strategically different and unexplored approaches to use ionic liquids (IL) containing weakly solvated and highly reactive chalcogenide anions [E‐SiMe3]− and [E−H]− of the heavy chalcogens (E=S, Se, Te) in materials synthesis near room temperature. The first strategy involves the synthesis of unprecedented trimethylsilyl chalcogenido metalates Cat+[M(E‐SiMe3)n]− (Cat=organic IL cation) of main group and transition metals (M=Ga, In, Sn, Zn, Cu, Ag, Au). These fully characterized homoleptic metalates serve as thermally metastable precursors in low‐temperature syntheses of binary, ternary and even quaternary chalcogenide materials such as CIGS and CZTS relevant for semiconductor and photovoltaics (PV) applications. Furthermore, thermally and protolytically metastable coinage metalates Cat+[M(ESiMe3)2]− (M=Cu, Ag, Au; E=S, Se) are accessible. Finally, the use of precursors BMPyr[E‐SiMe3] (E=Se,Te; BMPyr=1‐butyl‐1‐methylpyrrolidinium) as sources of activated selenium and tellurium in the synthesis of high‐grade thermoelectric nanoparticles Bi2Se3 and Bi2Te3 is shortly highlighted. The second synthesis strategy involves the metalation of ionic liquids Cat[S−H] and Cat[Se−H] by protolytically highly active metal alkyls or amides RnM. This rather general approach towards unknown chalcogenido metalates Catm[Rn‐1M(E)]m (E=S, Se) will be demonstrated in a research paper following this short review head‐to‐tail.

Enhanced thermoelectric efficiency of the bulk composites consisting of “Bi2Te3 matrix” and “filler Ni@NiTe2 inclusions”

Mixture of thermoelectric Bi2Te3 and ferromagnetic Ni powders was spark-plasma-sintered to prepare bulk composites with different Ni content (0.5 and 1.25 at.%). Hexagonal Bi2Te3, cubic Ni and trigonal NiTe2 phases coexist in the composites. The Bi2Te3 phase forms matrix of the composite, whereas the Ni and NiTe2 phases corresponds to filler. The filler is formed by Ni@NiTe2 (“core-shell”) inclusions. Forming “core-shell” inclusions is due to high-temperature diffuse redistribution of Ni during the composites sintering. Gradient distributions of Ni, Te and Bi exist within these inclusions. Embedding the Ni filler into the Bi2Te3 matrix lead to drastic decrease of electrical resistivity, decrease of Seebeck coefficient, and increase of thermal conductivity. As result, the composites demonstrate enhanced thermoelectric efficiency. Optimal combination of thermoelectric properties for the composite with x = 0.5 at.% leads to more than two-fold enhancement of the thermoelectric figure-of-merit (∼0.67 for the composite against ∼0.30 for reference Bi2Te3 sample).

Ultra-low lattice thermal conductivity and giant phonon–electric field coupling in hafnium dichalcogenide monolayers

Phonons in crystalline solids are of utmost importance in governing its lattice thermal conductivity (kL). In this work, kL in hafnium (Hf) dichalcogenide monolayers has been investigated based on ab initio DFT coupled to linearized Boltzmann transport equation together with single-mode relaxation-time approximation. Ultra-low kL found in HfS2 (2.19 W m−1 K−1), HfSe2 (1.23 W m−1 K−1) and HfSSe (1.78 W m−1 K−1) monolayers at 300 K, is comparable to that of the state-of-art bulk thermoelectric materials, such as, Bi2Te3 (1.6 W m−1 K−1), PbTe (2.2 W m−1 K−1) and SnSe (2.6 W m−1 K−1). Gigantic longitudinal-transverse optical (LO-TO) splitting of up to 147.7 cm−1 is noticed at the Brillouin zone-centre (Γ-point), which is much higher than that in MoS2 single layer (∼2 cm−1). It is driven by the colossal phonon–electric field coupling arising from the domination of ionic character in the interatomic bonds and Born effective or dynamical charges as high as 7.4e on the Hf ions, which is seven times that on Mo in MoS2 single layer. Enhancement in kL occurs in HfS2 (2.19 to 4.1 W m−1 K−1), HfSe2 (1.23 to 1.7 W m−1 K−1) and HfSSe (1.78 to 2.2 W m−1 K−1) upon the incorporation of the non-analytic correction term. Furthermore, the mode Grüneisen parameter is calculated to be as high as ∼2.0, at room temperature, indicating a strong anharmonicity. Moreover, the contribution of optical phonons to kL is found to be ∼12%, which is significantly high than that in single-layer MoS2. Large atomic mass of Hf (178.5 u), small phonon group velocities (4–5 km s−1), low Debye temperature (∼166 K), low bond and elastic stiffness (Young’s modulus ∼75 N m−1), small phonon lifetimes (∼6 ps), low specific heat capacity (∼17 J K−1 mol−1) and strong anharmonicity are collectively found to be the factors responsible for such a low kL. These findings would be immensely helpful in designing thermoelectric interconnects at the nanoscale and 2D material-based energy harvesters.

Effect of annealing temperature on thermoelectric properties of bismuth telluride thick film deposited by DC magnetron sputtering

We report the thermoelectric properties of thick bismuth-telluride (Bi2Te3) films deposited on polyimide substrates by DC magnetron sputtering and annealed at various temperatures (150–350 °C). The influence of annealing temperature on the microstructure and electronic structure of thick Bi2Te3 films is discussed. In this work, the annealed film at 250 °C has the best thermoelectric property due to highest electrical conductivity and Seebeck coefficient. The main effect of annealing temperature was really helpful to improve crystalline structure and enhance carrier mobility, whereas the carrier concentration was reduced due to the volatile of tellurium atom during annealing. Chemical states of bound and unbound atoms (Bi, Bi3+, Te, and Te2‐) on the surface play an important role in electrical properties. The exceed temperature caused the micro-crack formation and affect carrier transport by the scattering. The power factor of Bi2Te3 deposited by DC magnetron sputtering and annealed at 250 °C is comparable to the power factors of thick Bi2Te3 film deposited by various deposition techniques. The output power of single-leg, thick, thermoelectric Bi2Te3 film annealed at 250 °C as a function temperature generated a power of 0.98 μW at a temperature difference of 50 °C.

Combined hot extrusion and spark plasma sintering method for producing highly textured thermoelectric Bi2Te3 alloys

Hot extrusion is a promising method for producing high-performance thermoelectric bismuth telluride alloys because of its ability to create textured microstructures. However, hot extrusion is less favourable for scaling-up because of temperature and strain gradients along the radial direction, and only <110> -textured thermoelectric legs can be obtained because of the fibre-like texture. We suggest a way to overcome these disadvantages by implementing an additional spark plasma sintering process on a stack of extrudates. Using this combined process, we demonstrate the fabrication of 12 × 15 × 13 mm3 p-type (Bi0.2Sb0.8)2Te3 samples from extrudates that had originally been 3 mm in diameter. The evolution of sheet-like texture revealed by SEM, XRD, and EBSD allows us to obtain both <110> - and <001> -textured thermoelectric legs from a single specimen that are desirable for low- and high-temperature applications, respectively. Our results demonstrate the combined method as an industry-friendly process for fabricating high-performance thermoelectric materials.

Anisotropic Thermoelectric Properties of n-Type Te-Free (Bi, Sb)2Se3 with Orthorhombic Structure

Bi2Se3, a sister compound of the best room-temperature thermoelectric (TE) Bi2Te3, has been proven to undergo a transition from a rhombohedral phase to an orthorhombic phase by Sb-alloying. Te-free...

Ternary selenides A2Sb4Se8 (A = K, Rb and Cs) as an n-type thermoelectric material with high power factor and low lattice thermal conductivity: importance of the conformationally flexible Sb-Se-Se-Sb bridges.

We investigated the thermoelectric properties of the layered ternary selenides A2Sb4Se8 (A = K, Rb and Cs) and the lattice thermal conductivity of K2Sb4Se8 on the basis of DFT calculations, to find that these selenides are a high-performance n-type thermoelectric material. The Seebeck coefficients and power factors calculated for the electron carriers of A2Sb4Se8 (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi2Te3 and PbTe. The lattice thermal conductivity κlatt of K2Sb4Se8 is comparable to that of PbTe, well-known for its low lattice thermal conductivity. In terms of both electronic and phonon structures, the structural parts of the A2Sb4Se8 (A = K, Rb and Cs) phases crucial for their thermoelectric properties are the conformationally-flexible Sb–Se–Se–Sb bridges that interlink between their structurally rigid units.

Geometric optimization of two-stage thermoelectric generator using genetic algorithms and thermodynamic analysis

Multi-objective genetic algorithms are used to optimize the structure, assignment of configuration and load resistance of a two-stage thermoelectric generator, where Skutterudite and Bi2Te3 are chosen as upper stage and lower stage TE leg materials, respectively. Heat convection and radiation are considered on the top of the upper substrate. In the optimization process, the specific power and entropy generation rate are considered synchronously as objective functions to maximize the power output per unit area and to minimize the irreversibilities. The FEM is adopted in the simulation model, and the Seebeck effect, together with the Peltier effect, Joule heating, Thomson effect, and Fourier heat conduction phenomena are all considered in the simulation process. Shannon's entropy method is applied to select the best solution from the Pareto Frontier. Besides, the exergy destruction rate is analyzed, the results show that the exergy destruction rate increases as the load resistance increases. In addition, the different relationships between the load resistance and the voltage, power output, efficiency and entropy generation rate are presented. The principle of performance enhancement is also explained by comparing the ZT value along the TE legs. The optimization is important to the development of more compact and high-efficiency thermoelectric generators.