P-type BiSbTe Research Articles

Realizing high power factor in p-type BiSbTe flexible thin films via carrier engineering

Realizing high power factor in p-type BiSbTe flexible thin films via carrier engineering

Advancement of thermoelectric performances through the dispersion of expanded graphene on p-type BiSbTe alloys

ABSTRACT We demonstrated the systematic investigation of the graphene addition on the microstructural behaviour and concurrent thermoelectric properties of water-atomized p-type BiSbTe (BST)- based alloy using mechanical ball milling, and followed through the spark plasma sintering to fabricate a bulk compact specimen. X-ray diffraction results confirm the single phase of BST. The fracture surface of both specimen exhibits the homogenous distribution of grains with irregular shapes in a random alignment. The graphene in the BST provides an extra carrier transport leading to an increment in the carrier concentration (n) resulting in higher electrical conductivity (σ) for the BST + Graphene composite. The interface between two-dimensional (2D) graphene and bulk BST provides a larger degree of phonon scattering leading to a maximum reduced thermal conductivity (к) of 0.8 W m−1K−1 compared to pristine- BST (0.9 W m−1K−1) results in a maximum figure of merit (ZT) 1.1 at 400 K.

Enhanced output voltage of thermoelectric generators driven by alternate triboelectric charges

Here, we report a novel thermoelectric generator (TEG) design aimed at boosting output voltage through the incorporation of ionic materials (perfluoroalkoxy and Ni) with alternating triboelectric charges. The ionic materials are attached to the cooling part of p-type BiSbTe and n-type BiTeSe TEGs, respectively. This significantly increases the electric potential difference inside the p-n junction TEG from 7.14 to 12.12 mV at the temperature difference of 20 K and the enhanced output voltage is maintained over 24 h. Finally, a TEG consisting of 11 p-n junction legs generates an output voltage of 0.167 V and the charged energy of 10 mF-capacitor is also boosted within 21 s.

Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.

Microstructure change and thermal conductivity reduction in p-type Bi–Sb–Te thermoelectric materials using a metal fatty acid as process control agent

Nanostructuring of bulk thermoelectric materials has attracted interest as a promising approach to improve the thermoelectric performance by lowering the thermal conductivity through phonon scattering. In the present study, a metal fatty acid, which is widely used as a precursor that decomposes to form nanoparticles in colloidal chemistry, was used as a process control agent (PCA) in the ball milling for nanostructured bulk thermoelectric materials. A p-type Bi–Sb–Te alloy was ball-milled with different amounts of iron stearate PCA and sintered into bulk pellets. Microstructural analysis clearly showed that particle growth during sintering was suppressed and nanoinclusions were introduced in matrix, which resulted in an increased interface density and low thermal conductivity. As a result of further analysis of the decrease in thermal conductivity, it was found that the bipolar thermal conductivity was reduced, and thus the ZT was improved at high temperature.

Investigation of anisotropy in microstructure and thermoelectric properties of large-scaled p-type Bi–Sb–Te sintered body made by hot pressing

Investigation of anisotropy in microstructure and thermoelectric properties of large-scaled p-type Bi–Sb–Te sintered body made by hot pressing

Mediating Point Defects Endows n-Type Bi2 Te3 with High Thermoelectric Performance and Superior Mechanical Robustness for Power Generation Application.

Bi2 Te3 -related alloys dominate the commercial thermoelectric market, but the layered crystal structure leads to the dissociation and intrinsic brittle fracture, especially for single crystals that may worsen the practical efficiency. In this work, point defect configuration by S/Te/I defects engineering is engaged to boost thermoelectric and mechanical properties of n-type Bi2 Te3 alloy, which, coupled with p-type BiSbTe, shows a competitive conversion efficiency for the fabricated module. First, as S alloying suppresses the intrinsic antisite defects and forms a donor-like effect, electronic transport properties are optimized, associated with the decreased thermal conductivity due to the point defect scattering. The periodide compound TeI4 is afterward adopted to further tune carrier concentration for the realization of an optimal ZT. Finally, an advanced average ZT of 1.05 with ultra-high compressive strength of 230MPa is achieved for Bi2 Te2.9 S0.1 (TeI4 )0.0012 . Based on this optimum composition, a fabricated 17-pair module demonstrates a maximum conversion efficiency of 5.37% under the temperature difference of 250K, rivaling the current state-of-the-art Bi2 Te3 modules. This work reveals the novel mechanism of point defect reconfiguration in synergistic enhancement of thermoelectric and mechanical properties for durably commercial application, which may be applicable to other thermoelectric systems.

Large-scale SHS based 3D printing of high-performance n-type BiTeSe: Comprehensive development from materials to modules

Micro thermoelectric devices have a broad application prospect in confined space refrigeration and power generation of small nodes in the Internet of things. The leg performance, manufacturing efficiency and yield are very important for the industrial production of thermoelectric devices. Here, self-propagating high-temperature synthesis (SHS) and selective laser melting (SLM) technique are combined to directly form a dense and highly growth-oriented n-type BiTeSe material in large scale from raw materials of Bi, Te and Se powders. Ignoring the solid solution of a small amount of Se, the composition and structure analysis of the micro-region via transmission electron microscopy shows that Bi first reacts with Te to form BiTe compound in the molten pool of laser, and then Te reacts with the intermediate BiTe to form Bi2Te3 phase. In the next manufacturing process, a thin bulk material with a size of 60 × 30 × 0.5 mm3 can be printed out within 1 h. Because of the excellent mechanical properties, 4000 valid legs with a size of 0.4 mm × 0.4 mm in plane can be obtained successfully. Finally, a micro thermoelectric device is fabricated via using 3D-printed n-type BiTeSe and commercially hot extrusion p-type BiSbTe legs (28 pairs). For solid refrigeration, the maximum cooling temperature difference is about 44 °C and the maximum cooling power Qmax of the device is about 2.1 W when the input current Imax is about 1.1 A. For power generation, the open-circuit voltage Uoc is 324 mV and the maximum output power Pmax is 4.97 mW when ΔT is 40 K.

Microstructure Change and Thermal Conductivity Reduction in P-Type Bi–Sb–Te Thermoelectric Materials Using a Metal Fatty Acid as Process Control Agent

Microstructure Change and Thermal Conductivity Reduction in P-Type Bi–Sb–Te Thermoelectric Materials Using a Metal Fatty Acid as Process Control Agent

Development of High-Performance Thermoelectric Materials by Microstructure Control of P-Type BiSbTe Based Alloys Fabricated by Water Atomization.

Developing inexpensive and rapid fabrication methods for high efficiency thermoelectric alloys is a crucial challenge for the thermoelectric industry, especially for energy conversion applications. Here, we fabricated large amounts of p-type Cu0.07Bi0.5Sb1.5Te3 alloys, using water atomization to control its microstructure and improve thermoelectric performance by optimizing its initial powder size. All the water atomized powders were sieved with different aperture sizes, of 32–75 μm, 75–125 μm, 125–200 μm, and <200 μm, and subsequently consolidated using hot pressing at 490 °C. The grain sizes were found to increase with increasing powder particle size, which also increased carrier mobility due to improved carrier transport. The maximum electrical conductivity of 1457.33 Ω−1 cm−1 was obtained for the 125–200 μm samples due to their large grain sizes and subsequent high mobility. The Seebeck coefficient slightly increased with decreasing particle size due to scattering of carriers at fine grain boundaries. The higher power factor values of 4.20, 4.22 × 10−3 W/mk2 were, respectively, obtained for large powder specimens, such as 125–200 μm and 75–125 μm, due to their higher electrical conductivity. In addition, thermal conductivity increased with increasing particle size due to the improvement in carriers and phonons transport. The 75–125 μm powder specimen exhibited a relatively high thermoelectric figure of merit, ZT of 1.257 due to this higher electric conductivity.

Enhancing the power factor of p-type BiSbTe films via deposited with/without Cr seed layer

The thermoelectric effect is an efficient method to use waste heat as a primary source of electrical energy. Being a room temperature thermoelectric thin film, p-type BiSbTe is one of the best candidates owing to the combined high efficiency and large power factor for future technological applications. Novel approaches have emerged in recent decades with the aim of enhancing the thermoelectric properties of BiSbTe thin films. The method involves using Cr as an adhesion and seed layer for controlling microstructure and transport properties via the energy filtering of high-energy carriers. The heterostructure of Cr/BiSbTe film demonstrates the best electrical transport performance, where the Seebeck coefficient and the electrical conductivity are 425 µV/K and 25 S/m* 103 in the vicinity of room temperature. The power factor of Cr/BiSbTe was reported to be 6.8 mW/mK2 at 375 K, which was approximately seven times higher than the film without the Cr layer. We conclude that the inclusion of the Cr seed layer can notably improve the electrical transport properties of p-type BiSbTe films.

Liquid-Phase Manipulation Securing Enhanced Thermoelectric Performance of Ag2Se.

Developing n-type materials with high peak and/or average ZT (ZT is the figure of merit) is an urgent need for the lower ZT of the existing n-type BiTeSe materials compared with the p-type BiSbTe materials. Here, we demonstrate that liquid-phase sintering can lead to lowered thermal conductivity and an improved power factor in n-type Ag2Se, which originates from the greatly lowered electronic thermal conductivity attributed to the decreased mobility and improved Seebeck coefficients because of increased effective mass. Benefiting from this, the maximum ZT (ZTmax) of ∼1.21 and the average ZT (ZTave) of 1.06 are successfully achieved in polycrystalline Ag2Se. In this work, ZTave is the highest reported value, being 26% larger than that of Ag2Se reported. Our work shows that liquid-phase sintering to achieve improved thermoelectric (TE) performance opens a great opportunity for designing prospective thermoelectrics.

Morphological Analysis and Properties Evaluation of Electrodeposited Thick BiSbTe Films with Cooperative Interactions among Multiple Additives

As a cost-effective method, electrodeposition has been widely applied to synthesize materials for the fabrication of micro thermoelectric devices. However, it is hard to obtain smooth, compact and high-performance p-type BiSbTe films when the thickness becomes higher. In this work, multiple additives consist of PVA and saccharin sodium are firstly introduced into the electrolyte bath with the assistance of KCl for electrodeposition. The influence of different additives on reduction kinetics, morphology, stoichiometry and crystalline structure has been thoroughly explored. Besides the electrolyte concentration and the deposition potential, the pulse duration for pulsed deposition also significantly affects the stoichiometry. The smooth, compact and well-adherent films with ideal composition were successfully deposited for the thickness range from 4 to 100 μm. Crystallite size was much refined, and lattice strain slightly increased with the cooperative reaction of multiple additives. The measured Seebeck coefficient reached around 262 ± 25 μV K−1 for the deposited film with multiple additives, while that of the film with absence of additives was about 156 ± 14 μV K−1. The electric resistivity increased from 66 μΩ·m to 150 μΩ·m when PVA and saccharin sodium were introduced, but decreased to 81 μΩ·m after increasing the electrolyte conductivity through adding KCl.

Preparation and thermoelectric performance of nano rare-earth oxides dispersed p-type BiSbTe alloys by mechanical milling and spark plasma sintering

Simultaneously, the enhancement of power factor and reduction in thermal conductivity is a critical issue to improve the thermoelectric performance of a certain material. In the present work, the rare earth oxide, Pr6O11 was added to the Bi-Sb-Te material and the corresponding thermoelectric properties have been systematically investigated. The Seebeck coefficient was slightly improved due to the increase in effective mass by addition of rare earth oxides in BiSbTe matrix. The electrical conductivity was decreased with increasing rare earth oxide content due to the decreasing mobility owing to the carrier scattering at grain boundaries. The thermal conductivity was reduced of 8% for Pr6O11/BiSbTe composites in which the 4 wt% added Pr6O11 particles, act as a scattering center for middle to higher wavelength phonons and induce the phonon scattering. As a result, the maximum thermoelectric figure of merit, ZT of 0.71 was obtained for 2 wt% added BiSbTe/Pr6O11 composites at 350 K.

Magnetism-induced huge enhancement of the room-temperature thermoelectric and cooling performance of p-type BiSbTe alloys

Superparamagnetic Fe3O4 nanoparticles remarkably enhance the room-temperature thermoelectric and cooling performance of BiSbTe alloys.

Development of p-type Bi2−xSbxTe3 thermoelectric materials for power generation application exploiting synergetic effect of Sb alloying and repress process

Bi–Te based alloy compounds are currently the best-performing thermoelectric materials near room temperature. However, with the temperature increase, their conversion efficiency drops dramatically due to intrinsic excitation, thereby limiting their power generation application. In this study, for low-temperature thermoelectric power generation, we develop p-type Bi–Sb–Te alloys with the highest performance at a temperature of ~473 K. Here, we note that increasing the amount of Sb can effectively suppress intrinsic excitation, shifting the ZT peak towards higher temperatures. Moreover, we apply the repress process, through which microstructures such as grain boundaries and dislocations are developed in the material, which in turn reduces the thermal conductivity. As a result, a peak ZT of ~1.32 at 473 K is achieved for Bi0.3Sb1.7Te3 in the direction parallel to the pressure, which indicates its large application prospect for low-temperature thermoelectric power generation.

Reduction of thermal conductivity in Al2O3 dispersed p-type bismuth antimony telluride composites

In this work, BiSbTe/Al2O3 composites were prepared by incorporation of alumina (with 2, 4, and 6 wt%) particles into the p-type Bi–Sb–Te gas atomized powders via mechanical milling and, subsequently consolidated by spark plasma sintering (SPS). The Seebeck coefficient was significantly improved (over 41%) at 325 K, while the electrical conductivity was abruptly decreased for 6 wt% Al2O3 added BiSbTe/Al2O3 composites, which was mainly due to the decreases in carrier concentration, and energy filtering of carriers at interfaces. The thermal conductivity was eminently decreased over 27.5% for 6 wt% Al2O3 added BiSbTe/Al2O3 composites, was mainly attributed to the scattering of carriers and phonons at enormous grain boundaries as well as newly formed interfaces. The Vickers hardness of the BiSbTe/Al2O3 composites was improved compared to that of base matrix, and this was attributed to refinement of grains, and to a dispersion strengthening mechanism.

Optimization of annealing conditions to enhance thermoelectric performance of electrodeposited p-type BiSbTe thin films

In this work, we report the optimization of annealing process to improve the thermoelectric properties of pulse electrodeposited bismuth antimony telluride (Bi–Sb–Te) films by varying the annealing time-temperature profile. The innovative approach of sandwiched Te in between the Bi–Sb–Te layers aids in compensating the loss of tellurium during the annealing of BiSbTe thin films. An optimized Seebeck coefficient of 90.5 µV/K along with a power factor of 240 µW/mK2 is achieved for samples annealed at 350 °C for 1 h under N2 atmosphere with controlled heating and cooling rates. These improvements are attributed to a significant decrease in the carrier concentration as substantiated by the Hall measurements and to the increase in the crystallite size at the elevated temperatures as indicated by the X-ray diffraction pattern data. A comprehensive study on the annealing parameters reveals that the Seebeck coefficient and the electrical conductivity are considerably more sensitive to the annealing temperature than compared to the annealing time.

Enhanced room-temperature thermoelectric performance of p-type BiSbTe by reducing carrier concentration.

Improving room-temperature thermoelectric performance of p-type (Bi,Sb)2Te3 is essential for its practical application. However, the usual doping or alloying methods increase the carrier concentration and result in enhanced thermoelectric properties at high temperatures but not room temperature. In this work, we find that Ti is a promising dopant to shift the optimum thermoelectric properties of p-type (Bi,Sb)2Te3 to room temperature by reducing its carrier concentration. p-type Bi0.5Sb1.5−xTixTe3 samples with various Ti contents have been prepared using a simple melting method. The carrier concentration of Bi0.5Sb1.5−xTixTe3 is reduced by partially replacing Sb with Ti, leading to not only a significantly increased Seebeck coefficient but also an improved power factor near room temperature. Moreover, the total thermal conductivity near room temperature also decreases owing to the combined effect of decreased electrical conductivity and an anisotropic microstructure. An optimal zT value of ∼1.2 is achieved near room temperature for the sample containing 6 at% Ti, and its average zT value below 150 °C increases to ∼1.1, demonstrating the great potential of this material for room-temperature thermoelectric devices.

Enhanced thermoelectric properties by effective decoupling of electrical, thermal properties and seebeck coefficient through the addition of rare earth sesquioxides in p-type BiSbTe alloys

The decoupling between the electrical conductivity and thermal conductivity is a crucial challenge to elevate the figure of merit of a given thermoelectric material. In this research, thermoelectric properties of the rare-earths sesquioxides added Bi-Sb-Te material has been investigated systematically. The electrical conductivity (σ) is increased by increase in carrier concentration due to progressive movement of reduced Fermi level deeper into the valance band. Meanwhile, an effective mass of the rare earth added BiSbTe composites has been increased and contributed to the resonant distortion in density of states (DOS), that gives rises to the enhancement of Seebeck coefficient (α). Owing to the increment of both factors (σ &α), a considerable enhancement in power factor of 14% was achieved for the 2 wt% added BiSbTe/(x-wt%) Nd2O3 composites. The low content addition of rare earth oxide particles are potentially acts as scattering centers for mid to long wavelength phonons and reduced the thermal conductivity by 7%. The effective decoupling of the electrical and thermal properties by rare earths sesquioxides (Nd2O3) provides a 15% enhancement in thermoelectric figure of merit, ZT for 2 wt% added BiSbTe/(x-wt%)Nd2O3 composites.