P-type Bi0 Research Articles

Broadening the optimum thermoelectric power generation range of p-type sintered Bi0.4Sb1.6Te3 by suppressing bipolar effect

Bi2Te3-based compounds are well-known commercial thermoelectric materials near room temperature. However, the strong intrinsic excitations above 400 K severely deteriorate the ZT values and limit the applications of thermoelectric power generation. Here, we choose divalent Pb as an acceptor impurity to improve the thermoelectric performance of p-type Bi0.4Sb1.6Te3 sintered materials at higher temperature. Tiny Pb doping not only obviously suppresses the bipolar effect by increasing the hole concentrations, but also decreases the lattice thermal conductivity via introducing phonon scattering centers, such as grain boundaries, dislocations, and dislocation strains. Consequently, a peak ZT of 1.2 at 375 K and a ZTave of 1.1 from 300 to 500 K are realized. A thermoelectric module comprised of our Bi0.4Sb1.597Pb0.003Te3 and commercial Bi2Te2.5Se0.5 is constructed and the evaluated energy conversion efficiency can reach 5.1 % under a temperature difference of 200 K. This study demonstrates that tiny Pb-doped Bi0.4Sb1.6Te3 is promising for low-grade heat recovery.

Critical role of tellurium self-compensation in enhancing the thermoelectric performance of p-Type Bi0.4Sb1.6Te3 alloy

Traditionally, preparing p-type (Bi,Sb)2Te3 based materials by the combination of ball milling and hot pressing is regarded effective to reduce the lattice thermal conductivity and obtain high zT value. However, the deteriorated electrical transport properties and poor reproducibility restrict the further promotion of such technology. In this work, we prepare Bi0.4Sb1.6Te3 materials with Te self-compensation method, which leads to a high average zT value of 1.39 from 30 to 200 ℃ with significantly enhanced reproducibility. The Te self-compensation is found to be effective in manipulating the Bi(Sb)Te- and VTe2+ native defects in Bi0.4Sb1.6Te3 and thus suppress the “donor-like” effect caused by ball milling. The resulting enhanced carrier concentration further brings about a convergence of multi-valley bands, which leads to an increase in the density of states (DOS) near Fermi level and delays the onset of bipolar effect, in favor of improving electrical properties meanwhile reducing the bipolar thermal conductivity. Moreover, in the melting process, the excess Te facilitates the formation of Te-rich precipitates which remain in the ball-milled powders and then volatilize during the spark plasma sintering (SPS) process, thus leaving dispersedly distributed submicron pores and concequently reduced the lattice thermal conductivity. Taken together, the peak zT value reaches 1.55 at 100 ℃ and shows excellent reproducibility in three repeated measurements, which can promote the widespread application of the ball-milled (Bi,Sb)2Te3 based materials in solid-state refrigeration.

(Bi,Sb)2Te3/SiC nanocomposites with enhanced thermoelectric performance: Effect of SiC nanoparticle size and compositional modulation

Fabrication of nanoparticle-dispersed composites is an effective strategy for enhancing the performance of thermoelectric materials, and in particular SiC nanoparticles have been often used to create composites with Bi2Te3-based applied thermoelectric materials. However, the effect of particle size on the thermoelectric performance is unclear. This work systematically investigated the electrical and thermal properties of a series of (Bi,Sb)2Te3-based nanocomposites containing dispersed SiC nanoparticles of different sizes. It was found that particle size has a significant impact on the electrical properties with smaller SiC nanoparticles giving rise to higher electrical conductivity. Even though the dispersed SiC nanoparticles enhanced the Seebeck coefficient, no apparent dependence of the enhancement on the particle size was observed. It was also found that smaller SiC nanoparticles scatter phonons to some extent while the larger nanoparticles contribute to increased thermal conductivity. Eventually, the highest ZT value of 1.12 was obtained in 30 nm-SiC dispersed sample, corresponding to an increase by 18% from 0.95 for the matrix made from commercial scraps, and then the ZT was further boosted to 1.33 by optimizing the matrix composition and expelling excess Te during the optimized spark plasma sintering process. This work proves that the dispersion of smaller SiC nanoparticles in p-type (Bi,Sb)2Te3 materials is more effective than the dispersion of larger nanoparticles. In addition, it is revealed that additional compositional and/or processing optimization is vital and effective for obtaining further performance enhancement for nanocomposites of SiC nanoparticles dispersed in (Bi,Sb)2Te3.

Synergistic effects of B-In codoping in zone-melted Bi0.48Sb1.52Te3-based thermoelectric

Bismuth-telluride-based alloys are the unique commercial thermoelectric materials near room temperature, and the commonly used zone-melting method is efficient for the mass production. Since the ZTs of zone-melted samples has stagnated around 1.2 for decades, it is urgent for the scientific and industrial societies to break through this bottleneck. Herein, we report simultaneously improved power factor and ZT values in p-type Bi0.48Sb1.52Te3 materials by the addition of amorphous boron and metal indium. B and In dopants not only effectively increase the hole concentration and the density of state effective mass, leading to a high power factor of 55 μW cm−1 K−2, but also introduce various phonon scattering centers to obviously suppress the lattice thermal conductivity. The synergistic effects yield a ZTmax of 1.45 at 350 K, as well as a ZTave of 1.20 and σS2ave of 41 μW cm−1 K−2 (300 ~ 500 K) in the Bi0.48Sb1.515In0.005Te3 + 0.6 wt% B sample, suggesting tiny B-In codoping is a promising strategy for the further development of bismuth telluride thermoelectrics.

Formation of inhomogeneous micro-scale pores attributed ultralow κlat and concurrent enhancement of thermoelectric performance in p-type Bi0.5Sb1.5Te3 alloys

In the background of enhancing thermoelectric (TE) figure of merit of solid-state materials, the introduction of porous structure can significantly decrease lattice thermal conductivity by intensifying phonon scattering at the inhomogeneous microscale pores. Herein, we developed a porous structure in Cu0.07Bi0.5Sb1.5Te3 compounds by utilizing PVA as the pore former, and systematically studied its effect on thermoelectric properties. The results revealed that the reduction in thermal conductivity (~28%) was greater than the decrease in electrical conductivity (~17%) with increasing porosity, indicating long-wavelength phonon scattering was enhanced at micro-scale pores. Consequently, a peak zT of 1.342 at 400 K, and a zTavg of 1.254 in the temperature range of 300–500 K and an ηmax of ~9.4% at ΔT = 200 K were achieved in the porous sample (10.58%), which all are higher than that of dense sample. The hardness and compressive strength of the porous samples were significantly higher than commercial zone melting ingots. The proposed methodology is a cost-effective and efficient way of producing high-performance TE devices with good mechanical stability for real life practical applications.

Thermoelectric properties of p-type polycrystalline Bi0.8Sb0.8In0.4Se3

Achieving both n-type and p-type performance in one thermoelectric material family is of great benefit for the thermoelectric device due to the comparable mechanical properties. Bi2Se3 shows strong n-type behavior due to the intrinsic Se vacancy. Herein, we reported a p-type poly-crystalline Bi0.8Sb0.8In0.4Se3 material, which has the same crystalline structure as Bi2Te3, with an intrinsic Seebeck coefficient of 500 μV K−1 at room temperature. It is found that Mn is a good p-type charge carrier provider in the as-fabricated Bi0.8Sb0.8In0.4Se3 thermoelectric material. An optimized power factor of ∼420 μW m−1 K−2 and a low thermal conductivity of 0.51 W m−1 K−1 result in a ZT of 0.48 at 350 °C in Mn0.03Bi0.77Sb0.8In0.4Se3. Our work provides an incisive insight into the manipulation of the intrinsic defects via high entropy strategy.

High performance scalable and cost-effective thermoelectric devices fabricated using energy efficient methods and naturally occuring materials

Various printing methods have recently been employed to manufacture thermoelectric generators. While providing a scalable alternative to manufacturing thermoelectric generators, these printing techniques consume excessive energy by using long-duration and high-temperature sintering to reduce the interfacial connections and grain boundaries between thermoelectric particles. We report an inexpensive and energy-saving technique for fabricating thermoelectric generator devices that can be employed for low-waste heat applications. This technique involves a synergistic approach, using a small amount of binder (0.05 wt%), a heterogenous distribution of thermoelectric particles of varying size, low temperature (120 °C) and short duration (30 min) curing, and application of uniaxial mechanical pressure (200 MPa) to reduce the grain boundaries and interfacial connection and to enhance electrical conductivity of thermoelectric composite films and thermoelements. In this work, we present a thermoelectric prototype fabricated on gold-coated Kevlar substrate using p-type chitosan-100 mesh Bi0.5Sb1.5Te3 and n-type chitosan-100 mesh Bi composite inks. The dimension of a single thermoelement was 6.5 mm × 2.3 mm × 150 µm. The 9-couple planar device was able to produce a power output of 73 µW at a voltage of 26 mV, and at a current of 2.8 mA at a temperature difference of 40 K, which is sufficient to power wireless sensor devices. Using energy-efficient methods and naturally occurring materials (Bi and chitosan), this device achieved a power density of 566 µW/cm2 for a temperature difference of 40 K matching the best reported power densities of printed thermoelectric devices fabricated using high temperature and long duration.

A wearable real-time power supply with a Mg3Bi2-based thermoelectric module

A wearable thermoelectric generator using human body temperature is a promising power supply for wearable electronics. Here we discuss the design and fabrication of one kind of wearable thermoelectric generator constructed by n-type Mg3.2Bi1.498Sb0.5Te0.002 legs, p-type Bi0.4Sb1.6Te3 legs, polyurethane matrices, and flexible Cu/polyimide electrodes. The proposed device has a low thermal bypass and an efficient thermal contact interface, resulting in a peak power density of ∼20.6 μW/cm2 when placed on a human arm at an ambient temperature of 289 K (air velocity, 1.1 m/s) and a high peak power density of 13.8 mW/cm2 at a temperature difference of 50 K. In addition, it can withstand 10,000 bending cycles at a bend radius of 13.4 mm, suggesting that the proposed wearable thermoelectric generator has the potential to be a real-time power supply for certain wearable electronics in daily life.

Weak-ferromagnetism for room temperature thermoelectric performance enhancement in p-type (Bi,Sb)2Te3

Unceasing efforts have been devoted to performance enhancement of thermoelectric (TE) materials, and recently reports suggested a new approach by utilizing magnetism to increase power factor. This work investigated the doping effect of Fe on the TE properties of Bi2Te3-based materials. A series of Fex(Bi,Sb)2-xTe3 bulk samples were synthesized via mechanical alloying combined with spark plasma sintering. XRD results and DFT calculations indicate that Fe2+ and Fe3+ would coexist and substitute Bi3+ site firstly and shrink lattice. The co-doped Fe2+/Fe3+ in (Bi,Sb)2Te3 is helpful to reduce carrier concentration (nH), band gap (Eg) and increase effective mass (m∗). With further increase of x, ferromagnetic FeTe2 second phase was precipitated from (Bi,Sb)2Te3 matrix. A weak-ferromagnetism was observed in all Fe-doped samples via M-H curve, which could scatter low energy carriers along with little effect on high-energy carriers, whereby the mobility was enhanced effectively. Owing to the synergistic effect of weak-ferromagnetism and optimized band structure, the maximum power factor reaches up to 45 μWcm−1K−2 as x = 0.05, which is 28.5% higher than that at x = 0. The peak ZT value reaches up to 1.2 at 323 K along with a theoretical ηmax of 7.6% in the range of 303–473 K were achieved in x = 0.05 sample. The results suggest that introducing weak-ferromagnetism is an effective way to enhance room temperature TE performance of Bi–Sb–Te based materials.

High thermoelectric energy conversion efficiency of a unicouple of n-type Mg3Bi2 and p-type Bi2Te3

Low-grade heat harvesting by thermoelectric technology can contribute to efficient energy utilization. However, the large-scale application of thermoelectric devices is partially hindered by their unsatisfactory performance and relatively high cost. Here we prepared a cost-effective n-type Mg3Bi2-based compound with a peak zT of 1.24 at 573 K. A unicouple comprised of n-type Mg3.2Bi1.29Sb0.7Te0.01 and p-type Bi0.2Sb1.8Te3 was constructed and its energy conversion efficiency was evaluated. The unicouple exhibited a record-high efficiency of (9.0 ± 0.5)% or (8.3 ± 0.4)% [considering the radiation heat loss] under a temperature difference of 265 K at the hot-side temperature of 573 K. Our results demonstrate the great potential of Mg3Bi2-based materials for low-grade heat recovery.

Investigation of graphene dispersion on thermoelectric, magnetic, and mechanical properties of p-type Bi0.5Sb1.5Te3 alloys

In this research, polycrystalline p-type Bi0.5Sb1.5Te3 (BST)/x-wt% graphene (x = 0, 0.05, 0.1 and 0.2 wt%) composite bulks were fabricated to systematically investigate the effect of graphene content on thermoelectric, as well as magnetic and mechanical properties. The peaks corresponding to the D, G and 2D bands of graphene were clearly identified with Raman spectroscopy, and revealed that graphene was well dispersed in the BST matrix. The bulk fracture surfaces displayed randomly distributed grains and a progressive decrease in grain size, with increasing graphene content in the composite samples. A dramatic reduction in thermal conductivity of about 10%, and 12% was achieved for the 0.1, and 0.2 wt% graphene dispersed Bi0.5Sb1.5Te3 samples, respectively, due to the strong scattering of phonons at interfaces and fine grain boundaries. Thanks to the adequate power factor and the reduction in thermal conductivity by the incorporated graphene, the 0.1 wt% graphene dispersed Bi0.5Sb1.5Te3 sample showed the highest ZT value among all samples. Interestingly, a transformation from diamagnetic to para/ferro magnetic properties was observed after graphene incorporation, using magnetic hysteresis loops. Vickers hardness was also greatly improved, from 84.1 Hv to 103.8 Hv, and compressive strength was also increased. It was concluded that enhanced mechanical properties of the Bi0.5Sb1.5Te3 alloys was due to the strengthening effect of hierarchically structured graphene and reduced grain size.

Microstructure and thermoelectric performance evaluation of p-type (Bi, Sb)2Te3 materials synthesized using mechanical alloying and spark plasma sintering process

Microstructure and thermoelectric performance evaluation of p-type (Bi, Sb)2Te3 materials synthesized using mechanical alloying and spark plasma sintering process

Enhanced thermoelectric performance and atomic-resolution interfacial structures in BiSbTe thermo-electro-magnetic nanocomposites incorporating magnetocaloric LaFeSi nanoparticles

Incorporating magnetic nanoparticles in thermoelectric (TE) materials introduce magnetic interfaces with additional electron and phonon scattering mechanism for high TE performance. However, the influence of heterogeneous interfaces between magnetic nanoparticles and TE matrix on electronic and thermal transport remains elusive in the thermo-electric-magnetic nanocomposites. Here, using p-type TE material Bi0·3Sb1·7Te3 (BST) as matrix and magnetocaloric (MC) material La(Fe0·92Co0.08)11.9Si1.1 (LFS) nanoparticles as a second phase, TE/MC nanocomposites xLFS/BST (x = 0.1%, 0.2%, 0.3% and 0.4%) were synthesized using spark plasma sintering method. The atomic-resolution interfacial structures demonstrate that Te vacancies originating from LFS-BST interfacial reaction decreases the hole concentration of the LFS/BST nanocomposites and enhances the Seebeck coefficient. The LFS/BST nanocomposites exhibit lower thermal conductivity due to enhanced phonon scattering by interfaces and defects. All the nanocomposites have higher ZT than BST matrix, with 0.2%LFS/BST nanocomposite achieving highest ZT = 1.11 at 380 K. At working current 1.4 A, the device fabricated using 0.2%LFS/BST nanocomposite achieves maximal cooling temperature 4.9 K, which is 58% higher than the matrix. Moreover, the MC properties are retained in all the nanocomposites, which make them a promising candidate to achieve high TE performance and dual TE/MC properties for future applications.

Reduction of Thermal Conductivity Through Complex Microstructure by Dispersion of Carbon Nanofiber in p-Type Bi0.5Sb1.5Te3 Alloys

Reduction of Thermal Conductivity Through Complex Microstructure by Dispersion of Carbon Nanofiber in p-Type Bi0.5Sb1.5Te3 Alloys

Segregation of NiTe2 and NbTe2 in p-Type Thermoelectric Bi0.5Sb1.5Te3 Alloys for Carrier Energy Filtering Effect by Melt Spinning

The formation of secondary phases of NiTe2 and NbTe2 in p-type Bi0.5Sb1.5Te3 thermoelectric alloys was investigated through in situ phase separation by using the melt spinning process. Adding stoichiometric Ni, Nb, and Te in a solid-state synthesis process of Bi0.5Sb1.5Te3, followed by rapid solidification by melt spinning, successfully segregated NiTe2 and NbTe2 in the Bi0.5Sb1.5Te3 matrix. Since heterointerfaces of Bi0.5Sb1.5Te3 with NiTe2 and NbTe2 form potential barriers of 0.26 and 0.08 eV, respectively, a low energy carrier filtering effect can be expected; higher Seebeck coefficients and power factors were achieved for Bi0.5Sb1.5Te3(NiTe2)0.01 (250 μV/K and 3.15 mW/mK2), compared to those of Bi0.5Sb1.5Te3 (240 μV/K and 2.69 mW/mK2). However, there was no power factor increase for NbTe2 segregated samples. The decrease in thermal conductivity was seen due to the possible additional phonon scattering by the phase segregations. Consequently, zT at room temperature was enhanced to 0.98 and 0.94 for Bi0.5Sb1.5Te3(NiTe2)0.01 and Bi0.5Sb1.5Te3(NbTe2)0.01, respectively, compared to 0.79 for Bi0.5Sb1.5Te3. The carrier filtering effect induced by NiTe2 segregations with an interface potential barrier of 0.26 eV effectively increased the Seebeck coefficient and power factor, thus improving the zT of p-type Bi0.5Sb1.5Te3, while the interface potential barrier of 0.08 eV of NbTe2 segregation appeared to be too small to induce an effective carrier filtering effect.

Achieving superior performance in thermoelectric Bi0.4Sb1.6Te3.72 by enhancing texture and inducing high-density line defects

Miniaturization of efficient thermoelectric (TE) devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted (ZM) ingots. Here, we successfully prepared a robust high-performance p-type Bi0.4Sb1.6Te3.72 bulk alloy by combining an ultrafast thermal explosion reaction with the spark plasma sintering (TER-SPS) process. It is observed that the introduced excess Te not only enhances the (00l)-oriented texture to ensure an outstanding power factor (PF) of 5 mW m−1 K−2, but also induces extremely high-density line defects of up to 1011–1012 cm−2. Benefiting from such heavily dense line defects, the enhancement of the electronic thermal conductance from the increased electron mobility is fully compensated by the stronger phonon scattering, leading to an evident net reduction in total thermal conductivity. As a result, a superior ZT value of ~1.4 at 350 K is achieved, which is 40% higher than that of commercial ZM ingots. Moreover, owing to the strengthening of grain refinement and high-density line defects, the mechanical compressive stress reaches up to 94 MPa, which is 154% more than that of commercial single crystals. This research presents an effective strategy for the collaborative optimization of the texture, TE performance, and mechanical strength of Bi2Te3-based materials. As such, the present study contributes significantly to the future commercial development of miniature TE devices.

Performance assessment of nanostructured thermoelectric cooler

In this research study, 1D numerical simulation for p-type (Bi0.2Sb0.8)2Te3 nanocomposite thermoelectric cooler (TEC) is conducted by utilising a finite volume method. The model is verified through a comparison with the published analytical data and good agreement is observed. Multiwall carbon nanotube (MWCNT) is used to enhance the thermal characteristics of TEC which is represented by the figure of merit. In this context, three separate scenarios are developed for different MWCNT compositions in order to investigate the influence of various design parameters on the performance of TEC. It is found that the most efficient performance is achieved for nanocomposite containing 0.12 wt% of MWCNT with a figure of merit equal to 1.4. Moreover, the maximum value of exergy efficiency for this nanocomposite is found to be 0.195 at a current value of 0.7 A.

Performance assessment of nanostructured thermoelectric cooler

In this research study, 1D numerical simulation for p-type (Bi0.2Sb0.8)2Te3 nanocomposite thermoelectric cooler (TEC) is conducted by utilising a finite volume method. The model is verified through a comparison with the published analytical data and good agreement is observed. Multiwall carbon nanotube (MWCNT) is used to enhance the thermal characteristics of TEC which is represented by the figure of merit. In this context, three separate scenarios are developed for different MWCNT compositions in order to investigate the influence of various design parameters on the performance of TEC. It is found that the most efficient performance is achieved for nanocomposite containing 0.12 wt% of MWCNT with a figure of merit equal to 1.4. Moreover, the maximum value of exergy efficiency for this nanocomposite is found to be 0.195 at a current value of 0.7 A.

Development of Spark Plasma Syntering (SPS) technology for preparation of nanocrystalline p-type thermoelctrics based on (BiSb)2Te3

Bismuth antimony telluride is the most commonly used commercial thermoelectric material for power generation and refrigeration over the temperature range of 200–400 K. Improving the performance of these materials is a complected balance of optimizing thermoelectric properties. Decreasing the grain size of Bi0.5Sb1.5Te3 significantly reduces the thermal conductivity due to the scattering phonons on the grain boundaries. In this work, it is shown the advances of spark plasma sintering (SPS) for the preparation of nanocrystalline p-type thermoelectrics based on Bi0.5Sb1.5Te3 at different temperatures (240, 350, 400oC). The complex study of structural and thermoelectric properties of Bi0.5Sb1.5Te3 were presented. The high dimensionless thermoelectric figure of merit ZT ~ 1 or some more over 300–400 K temperature range for nanocrystalline p-type Bi0.5Sb1.5Te3 was obtained.

Novel p-n heterojunction Bi2O3/Ti3+-TiO2 photocatalyst enables the complete removal of tetracyclines under visible light

• The p-n heterojunction Bi 2 O 3 /Ti 3+ -TiO 2 photocatalyst was reported by a facile method. • The Bi 2 O 3 /Ti 3+ -TiO 2 enabled the complete removal (100%) of tetracyclines under visible light. • The effect of environmental factors on the photodegradation of tetracyclines was detailed. • The mechanism on photodegradation was analyzed through LC–MS spectrum. The search for a highly active visible-light photocatalyst toward the complete degradation of antibiotic residuals remains a challenging task due to the fast emergence of antibiotic resistance. To address the problem, we explore a novel p-n heterojunction visible-light photocatalyst by coupling a p-type Bi 2 O 3 with an n-type Ti 3+ self-doped TiO 2 porous material. The as-synthesized photocatalyst exhibits a narrowed bandgap (~2.89 eV) and enhanced visible-light absorption, leading to the complete degradation (100%) of antibiotics under visible light irradiation (λ > 420 nm) and excellent recyclability (98%) because of the synergistic effect of Ti 3+ self-doping and p-n heterojunction. The results effectively work out the challenging task of the incomplete removal of tetracyclines over almost all of the reported visible-light photocatalysts. Additionally, the effects of antibiotics mixture, pH value, inorganic ions, water matrix, and outdoor light on the degradation of tetracyclines were also detailed. Especially, the transformation pathways and degradation mechanism of tetracycline were revealed in depth via trapping experiments and photoelectrochemical characterizations. Therefore, this work provides a new insight in exploring excellent photocatalysts to realize the complete removal of other refractory organic pollutants under visible light.