Effects of hot pressing on electric performances of Bi0.5Sb1.5Te3

The effects of hot pressing on electric performance and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material prepared through vacuum melting and milling were studied. The phase constituent and microstructure were analyzed by X-ray Diffraction and cold field emission Scanning Electric Microscope. Aeolotropisms of the material on microstructure and electric performances are approved. With the rise of hot pressing temperature (from 300-500 ℃) and pressure (30-70 Mpa), electric conductivity and power factor are improved. Moreover, Bi0.5Sb1.5Te3 material can gain ideal thermoelectric performances and increased mechanical strength by hot pressing.     

Ga、K双掺杂P型Bi_(0.5)Sb_(1.5)Te_3材料的制备及热电性能

采用真空熔炼和热压方法制备了Ga和K双掺杂Bi0.5Sb1.5Te3热电材料。XRD结果表明,Ga0.02Bi0.5Sb1.48-x Kx Te3块体材料的XRD图谱与Bi0.5Sb1.5Te3的XRD图谱对应一致,但双掺杂样品的衍射峰略微向左偏移。热压块体材料中存在明显的(00l)晶面择优取向。SEM形貌表明材料组织致密且有层状结构特征。Ga和K双掺杂可使Bi0.5Sb1.5Te3在室温附近的Seebeck系数有一定的提高,而双掺杂样品的电导率均得到了不同程度的提高,其中Ga0.02Bi0.5Sb1.42K0.06Te3样品的电导率得到较明显的改善。在300~500 K测量温度范围内,所有双掺杂样品的热导率高于Bi0.5Sb1.5Te3的热导率,在300 K附近双掺杂样品的ZT值得到提高,其中Ga0.02Bi0.5Sb1.42K0.06Te3样品在300 K时ZT值达到1.5。     

定向生长Bi2Te3-Sb2Te3三元合金热电材料的组织与性能

利用Bridgman定向凝固法,在大凝固速率范围内5～1000μm/s制备出Bi2Te3-Sb2Te3三元合金块体热电材料,并对其凝固组织和不同凝固速率下合金的热电性能进行研究。结果表明:高温度梯度和大凝固速率范围内制备的25%Bi2Te3-75%Sb2Te3合金定向凝固组织由Bi0.5Sb1.5Te3单相组织组成;在较低凝固速率5μm/s下,熔体生长平界面失稳形成胞状组织,而随定向凝固速率的增加,胞状组织减少,组织细化。不同定向凝固速率下25%Bi2Te3-75%Sb2Te3合金的Seebeck系数和电阻率随着凝固速率的增加而增大。50μm/s下300～450K范围内获得功率因子(PF)在4.6×10-3～5.01×10-3W/(K2.m),并在350K时PF值达到最大值5.01×10-3W/(K2.m);而在高凝固速率500μm/s下,其功率因子也可达4.5×10-3W/(K2.m),表明高温度梯度和大凝固速率制备热电材料是一种有效的制备工艺方法。     

Thermoelectric properties of Bi_（1.5）Pb_（0.5）Sr_（2-x）La_xCo_2O_y polycrystalline materials

Polycrystalline samples of Bi 1.5 Pb 0.5 Sr 2-x La x Co 2 O y (x = 0.1, 0.2, 0.3) with a layered structure were prepared by solid-state reaction method. All samples are p-type semiconductors. The thermoelectric properties, namely, the electric resistivity (ρ), Seebeck coefficient (S), and power factor (S 2 /ρ) of the samples are dependent on chemical composition. The values of ρ, S, and S 2 /ρ increase with an increase in temperature for all samples. The substitution of Pb 2+ for Bi 3+ and La 3+ for Sr 2+ improves the thermoelectric properties of the Bi 2 Sr 2 Co 2 O y system owing to the simultaneous decrease of electric resistivity and increase of Seebeck coefficient. As a result, the optimal thermoelectric property has been obtained in Bi 1.5 Pb 0.5 Sr 1.7 La 0.3 Co 2 O y and the power factor can reach 2.1 × 10-4 W·m-1 K-2 at 998 K.     

Thermoelectric properties of Bi_(0.5)Sb_(1.5)Te_3/polyaniline composites prepared by mechanical blending and in-situ polymerization

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添加Sb的Ga2Te3合金热电性能

本研究采用等摩尔分数的Sb元素替换Ga2Te3中的Ga元素,并利用放电等离子烧结技术制备Ga1.9Sb0.1Te3合金,研究其微观结构和热电性能。结果表明,添加Sb元素后,材料的Seebeck系数为130～240μV/K,明显低于单晶Ga2Te3,电导率为3600～1740??1·m?1,至少是单晶Ga2Te3的17倍,热导率提高近25%。在649K时Ga1.9Sb0.1Te3合金的热电优值(ZT)达到最大值0.1,是同温度下单晶Ga2Te3ZT值的3倍。     

SPS法制备的三元合金Ag0.405Sb0.532Te的热电性能

采用放电等离子烧结法(SPS)制备了三元合金Ag0.405Sb0.532Te,并研究了它的输运性能,即Seebeck系数、电导率和热导率。结果表明,当温度从316K上升到548K时,电导率从7.6×104S·m-1下降到6.6×104S·m-1。在438K以上,热导率随温度上升逐渐增加,低于438K时,热导率趋于稳定,约为0.86W·(K·m)-1。无量纲热电优值ZT在548K时取得最大值0.65,稍高于Ag0.365Sb0.558Te三元合金的0.61。与掺Ag的AgxBi0.5Sb1.5-xTe3(x=0～0.4)合金相比,热电性能得到了改善。并再次讨论了AgxBi0.5Sb1.5-xTe3合金中析出的第二相Ag-Sb-Te三元合金的作用机制。     

急冷甩带过程和过量Te对p型Bi0.5Sb1.5Te3化合物热电性能的影响

采用感应熔炼制备得到了P型Bi0.5 Sb1.5Te3+x％(质量)Te(x=0、2、4和6)合金.将合金均匀分成R和S两组,R组不作处理,S组通过急冷甩带过程获得厚度约为5～15 μm的薄带,然后将两组样品分别粉碎过筛后,热压烧结成块体材料.利用扫描电镜(SEM)观察了薄带和烧结块体的形貌结构,在室温下测量其电性能....     

Bi-Te基热电材料的研究进展

阐述了Bi2Te3热电材料的基本特性，评述了Se，TeL4，SiC，RE（La，Ce等）的掺杂对BiTe材料热电性能的影响，以及国内外掺杂Bi—Te基热电材料的研究进展。介绍了Bi—Te基合金的制备技术的发展。最后指出通过材料的结构优化、组分调整及制备技术的改进，可以进一步提高材料的热电性能，得到理想的热电优值。     

Lifshitz topological impurity transitions in bismuth wires doped with acceptor and donor impurities

This paper reports the results of an experimental study of electronic topological transitions in bismuth glass-covered wires doped with acceptor (Sn) and donor (Te) impurities. The temperature dependences of the thermoelectric power and resistance are measured within the temperature range from 1.5 to 300 K and magnetic fields up to 14T. The position of the Fermi level ε_F and the concentration of charge carriers at doping are estimated from the Shubnikov de Haas (SdH) oscillations which are clearly visible from both L electrons and L and T holes in all crystallographic directions. We demonstrate anomalies in the temperature dependences of the thermopower in Bi wires doped with acceptor (Sn) and donor (Te) impurities in the form of a triple (doping by Sn) and double (doping by Te) change in the sign of the thermopower. The effect is interpreted with relation to the manifestation of impurity Lifshitz topological transitions. The SdH oscillation method was used to determine the energy position of the Σ band by doping Bi wires with the acceptor impurity Sn and the T band conduction by doping with Te. It is shown that the appearance of the Σ and T bands in Bi wires doped with the acceptor and donor impurities is responsible for the anomalies in the diffusive thermoelectric power, which gives a good conform with to the theoretical models and predictions.     

Phase formation and thermoelectric properties of Zn1+xSb binary system

The phase formation and thermoelectric (TE) properties in the central region of the Zn?Sb phase diagram were analyzed through synthesizing a series of Zn_1+xSb (x=0, 0.05, 0.1, 0.15, 0.25, 0.3) materials by reacting Zn and Sb powders below the solidus line of the Zn?Sb binary phase diagram followed by furnace cooling. In this process, the nonstoichiometric powder blend crystallized in a combination of ZnSb and β-Zn₄Sb₃ phases. Then, the materials were ground and hot pressed to form dense ZnSb/β-Zn₄Sb₃ composites. No traces of Sb and Zn elements or other phases were revealed by X-ray diffraction, high resolution transmission electron microscopy and electron energy loss spectroscopy analyses. The thermoelectric properties of all materials could be rationalized as a combination of the thermoelectric behavior of ZnSb and β-Zn₄Sb₃ phases, which were dominated by the main phase in each sample. Zn_1.3Sb composite exhibited the best thermoelectric performance. It was also found that Ge doping substantially increased the Seebeck coefficient of Zn_1.3Sb and led to significantly higher power factor, up to 1.51 mW·m^?1·K^?2 at 540 K. Overall, an exceptional and stable TE figure of merit (Z_T) of 1.17 at 650 K was obtained for Zn_1.28Ge_0.02Sb.     

Enhancing room-temperature thermoelectric performance of n-type Bi_2Te_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.     

悬浮熔炼制备Half-Heusler合金Zr1-xTixNiSn0.975Sb0.025及其热电性能

采用悬浮熔炼法合成了Zr1-xTixNiSn0.975Sb0.025(x = 0, 0.15, 0.25, 0.5)基Half-Heusler热电材料,X射线衍射结果表明所制备合金为单相.相对于常规方法,悬浮熔炼显著缩短了制备Half-Heusler合金的时间.同时研究了Ti取代及不同热压条件对材料热电性能的影响.结果表明:ZrNiSn0.975Sb0.025合金进行A位取代可降低材料的热导率,而不会明显影响其热电性能.致密度可以影响材料的热电性能,适当的热压条件可以使合金的ZT值达到最大,约为0.45.     

Ga、K双掺杂对N型Bi_2Te_(2.7)Se_(0.3)材料热电性能的影响

采用真空熔炼及热压方法制备了Ga和K双掺杂N型Bi2Te2.7Se0.3热电材料。XRD分析结果表明,Ga和K已经完全固溶到Bi2Te2.7Se0.3晶体结构中,形成了单相固溶体合金。SEM分析表明,材料组织致密且有层状结构特征。通过Ga和K部分替代Bi,在300~500 K的大部分温度范围内,Ga和K双掺杂对提高Bi2Te2.7Se0.3的Seebeck系数产生了积极的作用,同时双掺杂样品的电导率也得到明显的提高。Ga和K双掺杂样品的热导率都大于未掺杂的Bi2Te2.7Se0.3,Ga0.02Bi1.94K0.04Te2.7Se0.3合金在500 K获得ZT最大值为1.05。     

n 型 Bi-Te-Se 温差电材料溶液体系的电沉积过程研究

目的研究硫酸体系中元素铋、碲和硒的电沉积行为,为电沉积制备n型Bi2Te3-ySey温差电材料提供理论参考。方法采用电化学循环伏安测试技术,对硫酸溶液体系中铋、碲、硒三种元素的电沉积及不同元素间的共沉积过程进行研究。结果纯铋硫酸溶液体系中,Bi3+还原成单质铋的电化学反应是分步进行的,游离态和络合态的铋离子先后发生还原反应。纯碲硫酸溶液体系中,HTe O2+以吸附态和游离态两种形式先后发生还原反应。纯硒硫酸溶液体系中,溶液中的H2Se O3也通过分步还原反应生成硒单质。在Bi-Te-Se三元硫酸溶液体系中,Bi3+的浓度和基材对电沉积过程有显著影响,Bi-Te-Se化合物对电沉积过程具有促进作用。结论在Bi-Te-Se三元硫酸溶液体系中,Se,Te和Bi元素可依次在阴极表面发生还原反应而实现共沉积,从而制备出n型Bi-Te-Se温差电材料。     

Bi2-xSbxTe3热电薄膜的电化学沉积及表征

采用电化学沉积法,在ITO导电玻璃及钛片上沉积Bi2-xSbxTe3热电薄膜。采用循环伏安、SEM、XRD、EDX等技术分别对电化学沉积过程和薄膜的形貌、相结构、组成进行研究,并对其室温时的热电性能进行测试。结果表明,在含有Bi3＋、HTeO2+和SbO+的硝酸溶液中,采用控电位沉积模式,可以实现铋、锑、碲三元共沉积,得到Bi2-xSbxTe3薄膜。薄膜热处理前用冷等静压处理可以提高薄膜的密实度和平整度,并有利于热电性能的提高。     

Optimization of thermoelectric properties of n-type Bi_2(Te,Se)_3 with optimizing ball milling time

The thermoelectric properties at elevated temperature were investigated for n-type Bi2(Te,Se)3 which is obtained from ball milling processed powder with various milling times. Electrical properties such as electrical resistivity and Seebeck coefficient are clearly dependent on milling time, in which the carrier concentration is attributed to the change of the electrical properties. The concentrations of the defects are also varied with the ball milling time, which is the origin of the carrier concentration variation. Even though finer grain sizes are obtained after the long ball milling time, the temperature dependence of the thermal conductivity is not solely understood with the grain size, whereas the electrical contribution to the thermal conductivity should be also considered. The highest figure of merit value of ZT = 0.83 is achieved at373 K for the optimized samples, in which ball milling time is 10 h. The obtained ZT value is 48% improvement over that of the 0.5-h sample at 373 K.     

Effect of cooling rate on the thermoelectric and mechanical performance of Bi0.5Sb1.5Te3 prepared under a high magnetic field

Given the thermoelectric and mechanical performance of a given material is closely related to its microstructure, in this paper, the microstructure of p-type Bi_0.5Sb_1.5Te₃, fabricated by a high magnetic field assisted melting-solidification (HMAMS) process, is successfully tuned by regulating the cooling rate during the solidification process, and a systematic investigation has been carried out to the effect of the cooling rate on the crystal orientation, microstructure, thermoelectric and mechanical performance of the obtained materials. By this approach, the thermal conductivity is sharply reduced due to the intensive phonon scattering by the massive BST/Te and Te/BST_Ⅱ interfaces, while the power factor is less affected, and the flexural strength is enhanced owing to the narrowing of eutectic strip and spacing. Eventually, a highest ZT of 1.23 at 323 K with a maximal flexural strength 23.2 MPa has been obtained in the sample prepared under a 6 T magnetic field at a cooling rate of 16 K/min.     

Thermoelectric performance of p-type Bi–Sb–Te materials prepared by spark plasma sintering

In the present study, p-type (Bi,Sb)₂Te₃ thermoelectric materials have been fabricated through the spark plasma sintering (SPS) method by using powders with various particle sizes. Electrical conductivity (σ), Seebeck coefficient (), and thermal conductivity (κ) were evaluated in the temperature range of 300–500 K. The effect of annealing of the sintered samples on thermoelectric properties was also investigated. The maximum figure of merit ZT (ZT = ²σT/κ) of the sintered samples in the direction perpendicular to the pressing direction (with c-axis preferred orientation) was 1.15 at about 350 K, corresponding to be about 115% of that of the zone-melted ingot with the same composition in the same crystallographic orientation; while the bending strength was highly improved from about 10 to 80 MPa.     

Phase separation and thermoelectric properties of Ag2Te-doped PbTe0.9S0.1

Spinodal decomposition is an ideal mechanism for producing bulk nanostructured materials with promising thermoelectric (TE) performance. In this contribution, the phase separation and TE properties of PbTe-PbS samples are investigated. Phase separation driven by spinodal decomposition is observed in PbTe_0.4S_0.6, PbTe_0.5S_0.5, PbTe_0.6S_0.4 and (PbTe_0.9S_0.1)_1?x(Ag₂Te)_x with x = 0, 0.01 and 0.03. The addition of Ag₂Te leads to a deterioration in electrical transport properties at low temperature but to a significantly enhanced higher-temperature power factor of the Ag₂Te-doped PbTe_0.9S_0.1 sample. The very low thermal conductivity of the Ag₂Te-doped sample is attributed to the doping effect of Ag₂Te, the precipitated Ag₂Te, and the nanoscale phase segregation driven by spinodal decomposition. In particular, the spinodal decomposition produces finely dispersed PbTe-rich and PbS-rich phases with solute atoms, coherent or semicoherent interfaces, lattice bending, and other lattice defects, which contribute to the phonon scattering and minimize the thermal conductivity. The highest TE figure of merit, ZT, is ～1.2 at 773 K for the sample with x = 0.03, and even larger ZT values at higher temperature might be expected based on its tendency to increase with the temperature.