Additive-aided electrochemical deposition of bismuth telluride in a basic electrolyte

A new basic electrolyte with two cationic plating additives, polydiaminourea and polyaminosulfone, was investigated for the electrochemical deposition of the bismuth telluride film on a nickel-plated copper foil. Tellurium starts to deposit at a higher potential （-0.35 V） than bismuth （-0.5 V） in this electrolyte. The tellurium-to-bismuth ratio increases while the deposition potential declines from -1 to -1.25 V, indicating a kinetically quicker bismuth deposition at higher potentials. The as-deposited film features good adhesion to the substrate and smooth morphology, and has a nearly amorphous crystal structure disclosed by X-ray diffraction patterns.

Enhanced thermoelectric performance of n-type bismuth-telluridebased alloys via In alloying and hot deformation for mid-temperature power generation

Bismuth telluride-based alloys are the most widely used commercial thermoelectric(TE)material for room temperature refrigeration.Here,we successfully shift up the optimum figure of merit of n-type bismuth-telluride-based TE materials for mid-temperature power generation.SbI_(3)doping is used to regulate the carrier concentration and Indium alloying to increase the bandgap,suppressing the detrimental bipolar conduction in the mid-temperature range.The lattice thermal conductivity is significantly reduced due to the multiscale microstructures induced via hot deformation.As a result,a peak zT of~1.1 was attained at 625 K for Bi_(1.85)In_(0.15)Te_(2)Se+0.25 wt%SbI_(3)alloy after hot deformation,showing a great application prospect of this alloy in mid-temperature TE power generation.

Studying Thermoelectric Power Behaviors of Bi2Te3 Nanoparticles Prepared by Thermal Evaporation

Thin films of Bismuth Telluride (Bi2Te3) are prepared by thermal evaporation from nanopowders on the glass substrates. The XRD patterns of films show that all the films are polycrystalline and the crystalline increased by annealing temperature. Measuring of the thermoelectric power of thin films in the temperature range 300 to 380 K shows that Seebeck Coefficients have both negative and positive values, indicating that the films have both n-type and p-type conductivity. The re-crystallization of films is done by annealing from 130°C to 175°C and Seebeck Coefficient varied from -150 to 100 μV/K.

The Quantum Chemistry Calculation and Thermoelectricsof Bi-Sb-Te Series

The density junction theory and discrete variation method ( DFT - DVM) was used to study correlation between composition, structure, chemical bond, and property of thermoelectrics of Bi-Sb-Te series. 8 models of Bi20-xSbxTe32(x = 0,2,6,8,12,14,18 and 20) were calculated. The results show that there is less difference in the ionic bonds between Te( I)-Bi(Sb) and Te(Ⅱ)-Bi(Sb) , but the covalent bond of Te(Ⅰ)-Bi( Sb ) is stronger than that of Te(Ⅱ)-Bi( Sb ) . The interaction between Te(Ⅰ) and Te(Ⅰ) in different layers is the weakest and the interaction should be Van Der Wools power. The charge of Sb is lower than that of Bi, and the ionic bond of Te-Sb is weaker than that of Te-Bi. The covalent bond of Te-Sb is also weaker than that of Te-Bi. Therefore, the thermoelectric property may be imfiroved by adjusting the electrical conductivity and thermal conductivity through changing the composition in the compounds of Bi-Sb-Te. The calculated results are consistent with the experiments.

Optimization of p-type Segmented Bi_2Te_3/CoSb_3 Thermoelectric Material Prepared by Spark Plasma Sintering

A kind of p-type segmented Bi2 Te3/CoSB3 thermoetectric material was preparea oy sparse ptasma sintering（ SPS ） . When the segmented materials were used at the temperature ranging from 300 K to 800 K, the junction temperature was optimized, which is about 500 K, and the corresponding length ratio of CoSb3 to Bi2 Te3 is about 15 ： 2. The measured maximum power output of segmented materials is abont 320 W·m^-2, which is about 1.8 times as high as that of monolithic material CoSb3 under the same measuring conditions.

Origin of inhomogeneity in spark plasma sintered bismuth antimony telluride thermoelectric nanocomposites

Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices.However,the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far.Herein,we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride(BiSbTe)thermoelectric nanocomposites fabricated from solution-synthesized nanoplates.The figure of merit can reach 1.18,which,however,can be overestimated to 1.88 without considering the inhomogeneity.Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity,textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations.This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.

Thermoelectric transport enhancement of Te-rich bismuth antimony telluride(Bi_(0.5)Sb_(1.5)Te_(3+x))through controlled porosity

Alloys of Bi_(2)Te_(3) and Sb_(2)Te_(3) are the best performing p-type thermoelectrics near room temperature and have been the subject of extensive engineering efforts.Dramatic improvement is achieved by introducing defects that effectively scatter phonons and reduce thermal conductivity.Unfortunately,outstanding results are often difficult to reproduce as the process variables involved are difficult to control or possibly unknown.Here,a reproducible and controllable method of fabricating porous Bi_(0.5)Sb_(1.5)Te_(3+x) is presented.While effective medium theory(EMT)predicts no benefit,improvements in the thermoelectric quality factor,B(which determines the maximum zT of a materials),were as high as 45% parallel to the pressing direction for a sample of roughly 20% porosity.The study of microstructural evolution with increasing porosity is facilitated by a combination of Scanning/Transmission Electron Microscopy(S/TEM)and Electron Backscattered Diffraction(EBSD).This study reveals a statistically significant shift in the distribution of grain boundaries favoring lower energy twins,which coincides with an increase in the presence of stepped twin boundaries.This work demonstrates the potential benefits of careful grain boundary engineering and the need for further detailed studies of the dependence of thermal and electrical transport on grain boundary structure and orientation in these alloys.

Crystal defect engineering of Bi_(2)Te_(3)nanosheets by Ce doping for efficient electrocatalytic nitrogen reduction

Electrochemical nitrogen reduction reaction(NRR)is a promising method for the synthesis of ammonia(NH3).However,the electrochemical NRR process remains a great challenge in achieving a high NH3 yield rate and a high Faradaic efficiency(FE)due to the extremely strong N≡N bonds and the competing hydrogen evolution reaction(HER).Recently,bismuth telluride(Bi_(2)Te_(3))with two-dimensional layered structure has been reported as a promising catalyst for N_(2)fixation.Herein,to further enhance its NRR activity,a general doping strategy is developed to introduce and modulate the crystal defects of Bi_(2)Te_(3)nanosheets by adjusting the amount of Ce dopant(denoted as Ce_(x)-Bi_(2)Te_(3),where x represents the designed molar ratio of Ce/Bi).Meanwhile,the crystal defects can be designed and controlled by means of ion substitution and charge compensation.At−0.60 V versus the reversible hydrogen electrode(RHE),Ce_(0.3)-Bi_(2)Te_(3)exhibits a high NH_(3) yield(78.2μg·h^(−1)·mgcat^(−1)),a high FE(19.3%),excellent structural and electrochemical stability.Its outstanding catalytic activity is attributed to the tunable crystal defects by Ce doping.This work not only contributes to enhancing the NRR activity of Bi_(2)Te_(3)nanosheets,but also provides a reliable approach to prepare high-performance electrocatalysts by controlling the type and concentration of crystal defects for artificial N_(2)fixation.

纳米结构和能带工程提高Bi-Sb-Te合金的热电性能

碲化铋由于其优异的性能,已成为商业上广泛使用的热电材料.然而,通过熔化方法获得的p型Bi-Sb-Te热电材料的性能仍有进一步改进的空间.在这项工作中,CsBr化合物被用来提高Bi_(0.42)Sb_(1.58)Te_(3)(BST)材料的热电性能.采用熔化法和放电等离子体烧结相结合的方法制备了BST+x wt%CsBr(x=0,0.10,0.20,0.30)的块状材料.Cs和Br共掺杂可以显著提高BST合金的电导率,同时降低其热导率,使其在323 K下的最大ZT值为1.2.对于x=0.20的样品,在400 K以下具有1.1的平均ZT.密度泛函理论和透射电子显微镜分析表明,Cs掺杂有效地减小了带隙,增加了费米能级附近的态密度,并使能带变平缓,从而使电输运特性得到了明显增强(最大功率因子接近3500μW mK^(-2)).此外,Cs掺杂可以使得Sb从晶格中脱离出来并与晶格中的游离氧结合形成纳米级Sb_(2)O_(3),使其能够有效地散射中频声子并降低热导率,同时保持相对较高的塞贝克系数.这项研究提出了一种新的方法,可以仅单独通过CsBr掺杂来解决热电材料中电导率和热导率之间的矛盾.

Suppressing the donor-like effect via fast extrusion engineering for high thermoelectric performance of polycrystalline Bi_(2)Te_(2.79)Se_(0.21)

Bi2Te3-based alloys are the most mature commercial thermoelectric(TE)materials for the cooling application near room temperature.However,the poor mechanical properties of the commercial zone melting(ZM)ingot severely limits the further application.Meanwhile,due to the donor-like effect,the robust polycrystalline n-type bulks usually have low TE performance near room temperature.Herein,based on the commercial ZM ingots,a high figure of merit(zT)of 1.0 at 320 K and good mechanical properties are achieved via the hot extrusion.The dynamic recrystallization in the hot-extrusion process can suppress the donor-like effect and refine the large ZM grains into fine-equiaxed grains.Moreover,the obtained polycrystalline Bi2Te2.79Se0.21 has good preferential orientation and high carrier mobility(m).The high m and the weaken donor-like effect maintain the high power factor(PF)of 43.1 mW cm^(-1)K^(-2)in the hot-extruded ZM sample.Due to the enhanced phonon scattering,the total thermal conductivity ktot decreased to 1.35 W·m^(-1)·K^(-1).To demonstrate the good mechanical properties of the extruded ZM sample,micro TE dices with the cross sections of 300μm×300 mm and 200μm×200 mm are successfully cut from the extrusion sample.This study provided a fast and low-cost extrusion technique to improve the TE and mechanical properties of the commercial ZM ingot at room temperature.

Thermoelectric performance of p-type zone-melted Se-doped Bi_(0.5)Sb_(1.5)Te_3 alloys

For zone-melted （ZM） bismuth telluride-based alloys, which are widely commercially available for solidstate cooling and low-temperature power generation around room temperature, introducing point defects is the chief approach to improve their thermoelectric performance. Herein, we report the multiple effects of Se doping on thermoelectric performance of p-type Bi0.5Sb1,5Te3-xSex ＋ 3 wt% Te ZM ingots, which increases carrier concentration, reduces lattice thermal conductivity and deteriorates the carrier mobility. As a result, the peak figure of merit （ZT） is shifted to a higher temperature and a high ZT 1.2 at 350 K is obtained, due to the reduced thermal conductivity and suppressed intrinsic conduction. Further, decreasing Sb content is followed to optimize the room temperature performance and a ZT - 1.1 at 300 K is obtained. These results are significant for designing and optimizing the thermoelectric performance of commercial Bi0.5Sb1.5Te3＋ 3 wt% Te ZM alloys.

Enhanced thermoelectric properties of hydrothermally synthesized n-type Se&Lu-codoped Bi2Te3

N-type Se&Lu-codoped Bi2Te3 nanopowders were prepared by hydrothermal method and sintered by spark plasma sintering technology to form dense samples.By further doping Se element into Lu-doped Bi2Te3 samples,the thickness of the nanosheets has the tendency to become thinner.The electrical conductivity of Lu0.1Bi1.9Te3−xSex material is reduced with the increasing Se content due to the reduced carrier concentration,while the Seeback coefficient values are enhanced.The lattice thermal conductivity of the Lu0.1Bi1.9Te3−xSex is greatly reduced due to the introduced point defects and atomic mass fluctuation.Finally,the Lu0.1Bi1.9Te2.7Se0.3 sample obtained a maximum ZT value of 0.85 at 420 K.This study provides a low-cost and simple low-temperature method to mass production of Se&Lu-codoped Bi2Te3 with high thermoelectric performance for practical applications.

Enhanced linear magneto-resistance near the Dirac point in topological insulator Bi2(Te1−xSex)3 nanowires

We report the composition and back-gate voltage tuned transport properties of ternary compound Bi2(Te1−xSex)3 nanowires synthesized by chemical vapor deposition(CVD).It is found that the population of bulk carriers can be suppressed effectively with increasing the Se concentration x.In Bi2(Te1−xSex)3 nanowires with x=25%±5%,the ambipolar surface conduction associated with tuning the Fermi energy across the Dirac point of topological surface states is induced by applying a back-gate voltage.Importantly,we find that while the magnetoresistance(MR)follows the weak antilocalization(WAL)behavior when the Fermi level is tuned away from the Dirac point,MR is enhanced in magnitude and turns more linear in the whole magnetic field range(between±9 T)near the Dirac point.The observation of the enhanced linear magneto-resistance(LMR)and crossover from WAL to LMR,near the Dirac point provides a deeper insight into understanding the nature of topological insulator’s surface transport and the relation between these two widely observed magneto-transport phenomena.

Indentation fracture toughness of single-crystal Bi2Te3 topological insulators

Bismuth teUuride （Bi2Te3） is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their application in nanoelectronics. Determination of the fracture toughness plays a crucial role for the potential application of topological insulators in flexible electronics and nanoelectro- mechanical devices. Using depth-sensing nanoindentation tests, we investigated for the first time the fracture toughness of bulk single crystals of Bi2Te3 topological insulators, grown using the Bridgmantockbarger method. Our results highlight one of the possible pitfalls of the technology based on topological insulators.

Enhancing room-temperature thermoelectric performance of n-type Bi_(2)Te_(3)-based alloys via sulfur alloying

Bismuth-telluride-based alloys are the best thermoelectric materials used in commercial solid-state refrigeration near room temperature.Nevertheless,for n-type polycrystalline alloys,their thermoelectric figure of merit(zT) values at room temperature are often less than1.0,due to the high electron concentration originating from the donor-like effect induced by the mechanical deformation process.Herein,carrier concentration for better performance near room temperature was optimized through manipulating intrinsic point defects by sulfur alloying.Sulfur alloying significantly decreases antisite defects concentration and suppresses donor-like effect,resulting in optimized carrier concentration and reduced electronic thermal conductivity.The hot deformation process was also applied to improve carrier mobility due to the enhanced texture.As a result,a high zT value of 1 at 300 K and peak zT value of 1.1 at 350 K were obtained for the twice hot-deformed Bi_(2) Te_(2.7)Se_(0.21)S_(0.09) sample,which verifies sulfur alloying is an effective method to improve thermoelectric performance of n-type polycrystalline Bi2 Te3-based alloys near room temperature.

(Bi,Sb)_(2)Te_(3)/SiC纳米复合材料的热电性能增强:纳米SiC的尺寸和组分调控的影响

纳米复合是增强材料热电性能的有效手段,特别是纳米SiC粉末常被用来制备基于Bi_(2)Te_(3)的纳米复合材料,但是纳米粒子的尺寸对热电性能的影响并不清楚.本文中,我们制备了一系列不同粒度的纳米SiC弥散于BiSbTe基体的复合材料,并系统研究了其热电性能,发现纳米粒子的尺寸对BiSbTe材料电学性能有显著影响.小尺寸的纳米SiC复合会产生更高的电导率,纳米SiC的复合会增强材料的Seebeck系数,但这一增强与SiC的尺寸并无显著关联;另外,小尺寸的纳米SiC能够在一定程度上散射声子,而较大尺寸的纳米SiC却会使热导率增加,当纳米SiC尺寸为30 nm时,复合材料的ZT值达到了1.12,相比基体材料(ZT值为0.95)提高了18%.之后,通过优化基体组分、液相助烧以及优化烧结条件,材料的ZT值进一步提升到了1.33.本文证明,在BiSbTe材料中弥散分布小尺寸的纳米SiC能更有效地增强热电性能.此外,组分调控以及处理工艺的优化对于高性能的(Bi,Sb)_(2)Te_(3)/SiC纳米复合材料的获得必不可少.