N-type Bi Research Articles

High thermoelectric power factor of n-type Bi2(Se,S)3 via synergetic influence on the charge carrier concentration and energy filtering effect

Excellent thermoelectric performance is sought to address essential energy concerns, including the impact of energy consumption on the environment. In this work, we have synthesized the Bi2Se3 thin film using a simple thermal evaporation route and post‑sulfurized it for different durations at (773 K). The crystal structure change from rhombohedral to orthorhombic with different post‑sulfurization times has been confirmed via x-ray diffraction. The atomic vibrational modes of Bi2(Se,S)3 thin films have been examined by Raman spectroscopy. The surface morphology of Bi2(Se,S)3 thin films have been observed using a scanning electron microscope. The Seebeck coefficient values enhanced from 155.1 to 203.5 μV/K with post‑sulfurization time due to increased charge carrier concentration and energy filtering effect. The electrical conductivity improved from 90.2 to 118.7 S/m of the as-deposited sample to the highest post‑sulfurized sample due to improving charge carrier concentration and changing the crystal structure from rhombohedral to orthorhombic structure. We have achieved the maximum power factor of Bi2(Se,S)3 thin film of the 4.86 μWcm−1 K−2 at room temperature. Obtaining the highest power factor has a straightforward approach to fabricating commercial thermoelectric material.

Structural effects on the performance of microfabricated in-plane π -type thermoelectric devices composed of p-type Mg2Sn0.8Ge0.2 and n-type Bi layers

Miniaturized in-plane π-type thermoelectric devices composed of p-type Mg2Sn0.8Ge0.2 and n-type Bi layers were prepared by microfabrication techniques. Structural effects on thermoelectric device performance need to be evaluated and optimized to improve device performance and operation. In this study, a rational analysis of the correction of the open-circuit output voltages, output powers, and output power densities by using effective temperature differences was performed, and the effects of device geometries (e.g., the number of π junctions and the cross-sectional area ratio between p- and n-type layers) were determined by comparing different types of in-plane π-type thermoelectric devices. The results revealed that it is crucial to consider the heat transfer loss caused by thermal contact effects in the device and to optimize the structural geometries of the device. Proper structural trends and the effects of the number of p–n pairs on the device performance were observed, which indicated the reasonable device operation of microfabricated in-plane π-type thermoelectric devices.

Combinatorial screening via high-throughput preparation: Thermoelectric performance optimization for n-type Bi–Te–Se film with high average zT > 1

Thermoelectric materials have drawn extensive interest due to the direct conversion between electricity and heat, however, it is usually a time-consuming process for applying traditional “sequential” methods to grow materials and investigate their properties, especially for thermoelectric films that typically require fine microstructure control. High-throughput experimental approaches can effectively accelerate materials development, but the methods for high-throughput screening of the microstructures require further study. In this work, a combinatorial high-throughput optimization solution of material properties is proposed for the parallel screening and optimizing of composition and microstructure, which involves two distinctive types of high-throughput fabrication approaches for thin films, along with a new portable multiple discrete masks based high-throughput preparation platform. Thus, Bi2Te3–xSex thin film library with 196 throughputs for locating the optimized composition is obtained in one growth cycle. In addition, another thin film library composed of 31 materials with traceable process parameters is built to further investigate the relationship between microstructure, process, and thermoelectric performance. Through high-throughput screening, the Bi2Te2.9Se0.1 film with (00l) orientation is prepared with a peak zT value of 1.303 at 353 K along with a high average zT value of 1.047 in the interval from 313 to 523 K. This method can be also extended to the discovery of other functional thin films with a rapid combinatorial screening of the composition and structure to accelerate material optimization.

Modulation of Vacancy Defects and Texture for High Performance n-Type Bi2 Te3 via High Energy Refinement.

The carrier concentration in n-type layered Bi2 Te3 -based thermoelectric (TE) material is significantly impacted by the donor-like effect, which would be further intensified by the nonbasal slip during grain refinement of crushing, milling, and deformation, inducing a big challenge to improve its TE performance and mechanical property simultaneously. In this work, high-energy refinement and hot-pressing are used to stabilize the carrier concentration due to the facilitated recovery of cation and anion vacancies. Based on this, combined with SbI3 doping and hot deformation, the optimized carrier concentration and high texture degree are simultaneously realized. As a result, a peak figure of merit (zT) of 1.14 at 323 K for Bi2 Te2.7 Se0.3 + 0.05 wt.% SbI3 sample with the high bending strength of 100 Mpa is obtained. Furthermore, a 31-couple thermoelectric cooling device consisted of n-type Bi2 Te2.7 Se0.3 + 0.05 wt.% SbI3 and commercial p-type Bi0.5 Sb1.5 Te3 legs is fabricated, which generates the large maximum temperature difference (ΔTmax ) of 85 K at a hot-side temperature of 343 K. Thus, the discovery of recovery effect in high energy refinement and hot-pressing has significant implications for improving TE performance and mechanical strength of n-type Bi2 Te3 , thereby promoting its applications in harsh conditions.

Synergistically enhanced thermoelectric and mechanical performance of Bi2Te3 via industrial scalable hot extrusion method for cooling and power generation applications

To meet the fast-expanding needs of thermoelectric cooling for high heat flux systems, high-performance thermoelectric devices must be constructed with materials possessing both high thermoelectric properties and mechanical strength. However, the synergistic improvement of thermoelectric and mechanical properties is challenging because of the anisotropic thermal and electrical transports in the layered Van der Waals structure of Bi2Te3, particularly for n-type Bi2(TexSe1-x)3 material. The hot extrusion (HE) technique was believed as the most efficient approach to decoupling the thermoelectric and mechanical properties of Bi2Te3. However, the mechanism and performance of Bi2Te3 materials prepared by the HE method have been elusive. In this work, we developed an industrial-scalable HE technique to manipulate the texture ordering in Bi2Te3 material, achieving simultaneous improvement of thermoelectric and mechanical properties. Compared to SPS samples, our HE samples not only show 19% enhancement of the peak ZT, but also exhibit record high compressive strength of 205 MPa and flexural strength of 79 MPa, respectively. Furthermore, 7-pairs thermoelectric modules were fabricated to verify the cooling and power generation performance. A maximum temperature difference of 72 K (Th = 300 K) compared to 68 K for commercial devices and a maximum conversion efficiency of 5% at Th ≤ 500 K were realized.

Enhancement in figure of merit in N-type Bi(R)-Te thermoelectric nanomaterials

In this paper, we reported the cerium (Ce) doped thermoelectric materials with composition Bi2−xRxTe3 (R = Ce, x = 0.0, 0.1, and 0.2), which were prepared by using different wet chemical methods. The selected synthesis methods that were used included a simplified sol-gel method (Without Water and Surfactants-WOWS) and the Composite Mediated Hydrothermal Method (CMHM). The structural analysis of the samples showed rhombohedral and hexagonal structures. In addition, the surface morphology revealed a flower-like structure for the synthesized samples. The thermal stability was determined using differential scanning calorimetry and thermogravimetric analysis. The electrical conductivity of the samples with a doping ratio of x = 0.1 showed maximum conductivity of (19.10 × 103 (S/cm))-WOWS; (9.10 × 103 (S/cm)) – (CMHM) as compared to than that of other samples (x = 0.0 and 0.2). Interestingly, the doping of Ce increased the Seebeck effect, which also increased the power factor. The power factor of the samples x = 0.1 was higher than that of the undoped samples, which had a magnitude of 12.30 μW/cm.K2 (WOWS) and 7.02 μW/cm.K2 (CMHM). Moreover, we measured the thermal conductivity of the samples using the Advantageous Transient Plane Source (ATPS) method. Therefore, we found the higher figure of merit (ZT) value (0.41) at x = 0.1, which was prepared using a simplified sol-gel method, which is among the highest values that was reported for Bi2−xRxTe3 at room temperature. Because of its potential applications this material has great interest as a thermoelectric material and chip cooling sensing.

Effect of Surface Treatment of n-type Bi2Te3-based Materials on the Properties of Thermoelectric Units

Effect of Surface Treatment of n-type Bi₂Te₃-based Materials on the Properties of Thermoelectric Units

Design of N-Type Textured Bi2 Te3 with Robust Mechanical Properties for Thermoelectric Micro-Refrigeration Application.

Thermoelectric refrigeration is one of the mature techniques used for cooling applications, with the great advantage of miniaturization over traditional compression refrigeration. Due to the anisotropic thermoelectric properties of n-type bismuth telluride (Bi2 Te3 ) alloys, these two common methods, including the liquid phase hot deformation (LPHD) and traditional hot forging (HF) methods, are of considerable importance for texture engineering to enhance performance. However, their effects on thermoelectric and mechanical properties are still controversial and not clear yet. Moreover, there has been little documentation of mechanical properties related to micro-refrigeration applications. In this work, the above-mentioned methods are separately employed to control the macroscopic grain orientation for bulk n-type Bi2 Te3 samples. The HF method enabled the stabilization of both composition and carrier concentration, therefore yielding a higher quality factor to compare with that of LPHD samples, supported by DFT calculations. In addition to superior thermoelectric performance, the HF sample also exhibited robust mechanical properties due to the presence of nano-scale distortion and dense dislocation, which is the prerequisite for realizing ultra-precision machining. This work helps to pave the way for the utilization of n-type Bi2 Te3 for commercial micro-refrigeration applications.

Broad Temperature Plateau for High Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 by 3D Printing-Driven Defect Engineering

High-energy-conversion Bi2Te3-based thermoelectric generators (TEGs) are needed to ensure that the assembled material has a high value of average figure of merit (ZTave). However, the inferior ZTave of the n-type leg severely restricts the large-scale applications of Bi2Te3-based TEGs. In this study, we achieved and reported a high peak ZT (1.33) of three-dimensional (3D)-printing n-type Bi2Te2.7Se0.3. In addition, a superior ZTave of 1.23 at a temperature ranging from 300 to 500 K was achieved. The high value of ZTave was obtained by synergistically optimizing the electronic- and phonon-transport properties using the 3D-printing-driven defect engineering. The nonequilibrium solidification mechanism facilitated the multiscale defects formed during the 3D-printed process. Among the defects formed, the nanotwins triggered the energy-filtering effect, thus enhancing the Seebeck coefficient at a temperature range of 300-500 K. The effective scattering of wide-frequency phonons by multiscale defects reduced the lattice thermal conductivity close to the theoretical minimum of ∼0.35 W m-1 k-1. Given the advantages of 3D printing in freeform device shapes, we assembled and measured bionic honeycomb-shaped single-leg TEGs, exhibiting a record-high energy conversion efficiency (10.2%). This work demonstrates the great potential of defect engineering driven by selective laser melting 3D-printing technology for the rational design of advanced n-type Bi2Te2.7Se0.3 thermoelectric material.

Probing of Bi doped GeTe thermoelectrics leads to revelation of resonant states

Quest for lead free high performance mid temperature thermoelectric materials has led to extensive research on SnTe and GeTe based materials. Among various strategies implemented to improve the transport properties of GeTe, electronic structure engineering holds a prominent place. Herein, we reinvestigate the impact of substitutional doping of Bi in GeTe on its electronic structure in both rhombohedral and cubic phase. We uncover that Bi introduces resonance levels in GeTe acting as a first n-type resonant dopant in both rhombohedral and cubic phases. We also report for the first time that Bi resonance states undergo Rashba splitting in low temperature rhombohedral phase. Bi doping acts in a multifunctional way by tuning the carrier concentration, causing conduction band convergence and phonon scattering in addition to improving the band effective mass by distorting the density of states near the Fermi level to enhance the thermoelectric performance of the material. The convergence of L, Z and Σ valence bands in rhombohedral phase due to Bi doping leads to manifestation of Rashba effect in p-type material which was not reported till date. Thus, we propose that the chemical potential tuning can result in p-type as well as n-type Bi doped GeTe for thermoelectric application.

Modulation Doping Enables Ultrahigh Power Factor and Thermoelectric ZT in n-Type Bi2 Te2.7 Se0.3.

Bismuth telluride‐based thermoelectric (TE) materials are historically recognized as the best p‐type (ZT = 1.8) TE materials at room temperature. However, the poor performance of n‐type (ZT≈1.0) counterparts seriously reduces the efficiency of the device. Such performance imbalance severely impedes its TE applications either in electrical generation or refrigeration. Here, a strategy to boost n‐type Bi2Te2.7Se0.3 crystals up to ZT = 1.42 near room temperature by a two‐stage process is reported, that is, step 1: stabilizing Seebeck coefficient by CuI doping; step 2: boosting power factor (PF) by synergistically optimizing phonon and carrier transport via thermal‐driven Cu intercalation in the van der Waals (vdW) gaps. Theoretical ab initio calculations disclose that these intercalated Cu atoms act as modulation doping and contribute conduction electrons of wavefunction spatially separated from the Cu atoms themselves, which simultaneously lead to large carrier concentration and high mobility. As a result, an ultra‐high PF ≈63.5 µW cm−1 K−2 at 300 K and a highest average ZT = 1.36 at 300–450 K are realized, which outperform all n‐type bismuth telluride materials ever reported. The work offers a new approach to improving n‐type layered TE materials.

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.

High near-room temperature figure of merit of n-type Bi2GeTe4-based thermoelectric materials via a stepwise optimization of carrier concentration

• Stepwise carrier concentration optimization of Bi 2 GeTe 4 thermoelectric materials. • Ge vacancy-engineering transfer Bi 2 GeTe 4 into highly degenerated semiconductor. • Carrier concentration optimization leads to high power factor of 4.2 μW cm −1 K −2 . • Approaching a record-high zT value of ∼ 0.22 at 423 K in Bi 2 Ge 1.45 Te 4 . Bi 2 GeTe 4 is a promising near room-temperature thermoelectric candidate with a low lattice thermal conductivity. Carrier concentration of intrinsic Bi 2 GeTe 4 changes dramatically with tiny Ge content adjustment, leading to a challenge in carrier concentration optimization. To overcome this challenge, we firstly introduce excessive Ge into Bi 2 GeTe 4 to shift the Fermi level deep into the conduction band and transfer Bi 2 GeTe 4 into a highly degenerate n-type semiconductor. Secondly, the embedded p-type Bi 2 Ge 2 Te 5 secondary phase induces further optimization of the Fermi level and carrier concentration. Finally, the power factor of the as-synthesized Bi 2 GeTe 4 -based material is significantly increased from ∼ 0.08 μW cm −1 K −2 to ∼ 4.2 μW cm −1 K −2 at 423 K when increasing the nominal Ge content (x) of Bi 2 Ge x Te 4 from 1 to 1.45. Correspondingly, a high figure-of-merit of ∼ 0.22 at 423 K is achieved in Bi 2 GeTe 4 -based thermoelectric materials. This result indicates our viable stepwise strategy can be used to optimize carrier concentration and achieve high thermoelectric performance of the n-type Bi 2 GeTe 4 .

Energy filtering and phonon scattering effects in Bi2Te3–PEDOT:PSS composite resulting in enhanced n-type thermoelectric performance

We blend n-type Bi2Te3 with an inexpensive abundant conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), to gain a bulk-structured composite, in which energy filtering and phonon scattering effects should occur at the interface of two components. The composite records somewhat higher electrical resistivity than pristine Bi2Te3, because the interface possibly interrupts carrier transport. However, the composite completely compensates for the resistivity increment with a significant increase in the Seebeck coefficient, which is caused by energy filtering effects at the interface; thus, it exhibits the improved power factor. The composite also records a much lower thermal conductivity than the pristine Bi2Te3 because of phonon scattering effects at the interface. The composite induces significant decoupling of electrical and thermal properties, thus affording the remarkably enhanced figure of merits (ZTmax ∼ 1.19 at 132 °C, ZTave ∼ 1.14 at 50–150 °C), which are approximately double those of the pristine Bi2Te3. The ZT values are not only predominant among the performance of n-type binary Bi2Te3, but they are also as competent as the excellent performance of n-type ternary Bi2(Te,Se)3 previously reported.

Nanostructured ZnSb films composited with Bi2Te3 topological insulators exhibit strongly unusual p–n conduction conversion upon crystallization

The crystallization of a local p-type ZnSb material can be deterministically tuned by doping with the n-type topological insulator Bi 2 Te 3 . Upon annealing, pure ZnSb shows a transition across three states, namely, high resistance, intermediate resistance, and low resistance. The metastable intermediate ZnSb phase has p-type conduction. Here, we find that the metastable ZnSb phase of the pure ZnSb film is significantly suppressed by Bi 2 Te 3 doping, and the underlying conduction is changed into n-type conduction because Bi 2 Te 3 doping induces a change in crystallization and simultaneously changes the type of crystalline phases. Nanoprecipitate formation and crystallization transition are the driving forces of the composition-dependent p–n conduction conversion. The X-ray diffraction, X-ray photoelectron and Raman spectroscopy results of the crystalline thin films suggest that the local bonding arrangement around Sb atoms changes. The Bi–Sb topological insulators are thus mainly responsible for the p–n transition and ultralow resistance shift shown by ZnSb–Bi 2 Te 3 alloys.

Bi(2-x)SbxTe3 Thermoelectric Composites with High Average zT Values: From Materials to Devices

(Bi,Sb)Te-based materials have drawn extensive attention for nearly two centuries as one of the most successful commercial thermoelectric (TE) materials. However, Bi(2-x)SbxTe3 composites with remarkable average figure of merit (zTavg) values are highly desired in terms of the great contribution on expanding the applying temperature ranges of the commercial devices. Herein, Bi0.35Sb1.65Te3 compound with outstanding zTavg value of about 1.18 (integrate from 298 to 498 K) was obtained via delaying the bipolar effect by precipitating multi-scale Sb2Te3 inclusions. The power factor (PF) was enhanced from 2.1×10−3 Wm−1 K−2 (Bi0.5Sb1.5Te3) to 4.3×10−3 Wm−1 K−2 (Bi0.35Sb1.65Te3) by optimizing the carrier concentration from 1.9×1019 cm−3 to 3.9×1019 cm−3 via adjusting the proportions of Bi:Sb. Correspondingly, the lattice thermal conductivities (kl) were distinctly suppressed by the additional multiple phonon scattering resulting from the Sb2Te3 precipitates. Consequently, a remarkable zTmax, as high as ~1.35 at 373 K was obtained in the Bi0.35Sb1.65Te3 sample. The temperature difference ( T, 6.0 A current) of the TE device that assembled with the commercial N-type Bi(Te,Se) ingot has reached up to 66.9 K. The high zTavg, zTmax and T values will further promote the commercial applications of (Bi,Sb)Te-based materials in a wide temperature range.

Visible-light induced CoMoO4@Bi2MoO6 heterojunction membrane with attractive photocatalytic property and high precision separation toward oil-in-water emulsion

• A novel synthetic strategy was proposed to facilitate the preparation of NF@CM@BM heterojunction membrane. • The synergistic application of photocatalysis and special wettability for oily wastewater remediation. • The NF@CM@BM heterojunction membrane exhibits excellent separation performance toward oil-in-water emulsions. • The formation of p-n heterojunction between p-type CoMoO 4 and n-type Bi 2 MoO 6 greatly enhances the photocatalytic ability. • Possess favorable stability, recyclability and self-cleaning property. The discharge of wastewater containing insoluble oils and water-soluble organic pollutants has caused severe water pollution and seriously threatened the sustainable development of human society. Membrane separation technology, on the basis of the size sieving and superwettability, can effectively remove insoluble oils from the wastewater, but still lacking the ability to degrade water-soluble pollutants. Herein, a novel heterojunction membrane with dual functionalities of superhydrophilicity and visible-light photocatalytic property was prepared by constructing hierarchical CoMoO 4 @Bi 2 MoO 6 nanoarrays on Ni foam (NF@CM@BM) via a facile two-step hydrothermal process combined with calcination methods. Attributed to the synergistic application of photocatalysis, superhyophilicity and underwater superoleophobicity, the membrane could simultaneously remove water-soluble organic pollutants and insoluble oils in wastewater efficiently. Completely driven by gravity, high oil/water separation efficiency of 99.67% could be achieved with the flux of 1449.12 L m -2 h −1 . Besides, the formation of p-n heterojunction between p-type CoMoO 4 and n-type Bi 2 MoO 6 greatly enhanced the photocatalytic ability to degrade Congo red with the efficiency of 97.1%. More importantly, the NF@CM@BM membrane exhibited excellent stability and recyclability, possessing great application potential in oily wastewater remediation. Therefore, we envision that this work will offer new insights into the design of wastewater remediation membranes.

Thermoelectric Properties of SiC-Nanocomposite n-Type Bi2(Te0.90Se0.10)3 Prepared by Mechanical Alloying and Microwave Sintering

Thermoelectric Properties of SiC-Nanocomposite n-Type Bi2(Te0.90Se0.10)3 Prepared by Mechanical Alloying and Microwave Sintering

A Novel Method to Significantly Improve the Mechanical Properties of n-Type Bi(1−x)Sbx Thermoelectrics Due to Plastic Deformation

A unique method was developed to significantly improve the strength of Bi(1−x)Sbx single crystals, the most effective thermoelectric (TE) materials in the temperature range from 100 to 200 K due to their plastic deformation by extrusion. After plastic deformation at room temperature under all-round hydrostatic compression in a liquid medium, n-type Bi–Sb polycrystalline solid solutions show a significant increase in mechanical strength compared to Bi–Sb single crystals in the temperature range from 300 to 80 K. The significantly higher strength of extruded alloys in comparison with Bi–Sb single crystals is associated with the development of numerous grains with a high boundary surface as well as structural defects, such as dislocations, that accumulate at grain boundaries. Significant stability of the structure of extruded samples is achieved due to the uniformity of crystal plastic deformation under all-round hydrostatic compression and the formation of the polycrystalline structure consisting of grains with the orientation of the main crystallographic directions close to the original single crystal. The strengthening of Bi–Sb single crystals after plastic deformation allows for the first time to create workable TE devices that cannot be created on the basis of single crystals that have excellent TE properties, but low strength.

Boron‐Mediated Grain Boundary Engineering Enables Simultaneous Improvement of Thermoelectric and Mechanical Properties in N‐Type Bi2Te3

Powder metallurgy introduces small structures of high-density grain boundaries into Bi2 Te3 -based alloys, which promises to enhance their mechanical and thermoelectric performance. However, due to the strong donor-like effect induced by the increased surface, Te vacancies form in the powder-metallurgy process. Hence, the as-sintered n-type Bi2 Te3 -based alloys show a lower figure of merit (ZT) value than their p-type counterparts and the commercial zone-melted (ZM) ingots. Here, boron is added to one-step-sintered n-type Bi2 Te3 -based alloys to inhibit grain growth and to suppress the donor-like effect, simultaneously improving the mechanical and thermoelectric (TE) performance. Due to the alleviated donor-like effect and the carrier mobility maintained in our n-type Bi2 Te2.7 Se0.3 alloys upon the addition of boron, the maximum and average ZT values within 298-473 K can be enhanced to 1.03 and 0.91, respectively, which are even slightly higher than that of n-type ZM ingots. Moreover, the addition of boron greatly improves the mechanical strength such as Vickers hardness and compressive strength due to the synergetic effects of Hall-Petch grain-boundary strengthening and boron dispersion strengthening. This facile and cost-effective grain boundary engineering by adding boron facilitates the practical application of Bi2 Te3 -based alloys and can also be popularized in other thermoelectric materials.