Bi0.5Sb1.5Te3/Bi2Te2.4Se0.6 thin film thermoelectric sensors

In order to make thin film thermoelectric sensors, p-type (Bi_0.5Sb_1.5Te₃) and n-type (Bi₂Te_2.4Se_0.6) thermoelectric thin films were deposited on Pyrex and Teflon substrates by the flash evaporation technique. Their thermoelectric properties were investigated for annealed (473 K, 1 h) films. Thin film temperature sensors were fabricated and their thermal emf, sensitivity, and time constant were measured and evaluated. The sensor deposited on Teflon substrate showed better performance than that on the Pyrex substrate. The sensitivity and time constant were 2.54 V/W and 13.7 s, respectively, for the sensor with a leg size of 3 mm (w)×16mm (l)×4μm (t).     

Bi2Te3片式阵列的制备及生成机理

以Bi（NO3）3和Te为反应物，在乙二胺四乙酸二钠（EDTA-2Na）、N，N-二甲基甲酰胺（DMF）与乙醇组成的混合溶剂以及过量强碱KOH的作用下，通过溶剂热反应，制得Bi2Te3热电材料的片式阵列纳米结构。利用XRD、SEM、EDX对产物的物相、形貌及成分进行了表征和研究。通过实验研究推断这种BizTe，片式阵列的形成过程可能是一个络合-成核-生长-脱离-组装的过程。     

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。     

Synthesis of nanocrystalline Bi2Te3 via mechanical alloying

Bi₄₀Te₆₀ thermoelectric compound was fabricated via mechanical milling of bismuth and tellurium as starting materials. Effect of the milling time and heat treatment temperatures were investigated. In order to characterize the ball milled powders, the X-ray diffraction (XRD) was used. Thermal behavior of the mechanically alloyed powders was studied by differential thermal analysis (DTA). The morphological evolutions were studied by scanning electron microscopy (SEM). Results showed that the nanocrystalline Bi₂Te₃ compound was formed after 5 h of milling. Further milling (25 h) and heating to 500 °C showed that the synthesized phase was stable during these conditions. Nanocrystalline Bi₂Te₃ with 9–10 nm mean grain size and flaky morphology (lamellar structure) was obtained at the end of milling.     

Bi2Te3纳米颗粒和纳米线的溶剂热合成及组织特征

分别以吡啶、无水乙醇为反应介质,以NaBH4为还原剂,采用溶剂热合成方法,在150℃下反应24 h制备了平均晶粒尺寸为15～20 nm的Bi2Te3纳米粒子.采用相同的合成方法,以去离子水为反应介质,合成了直径为30～80 nm,长径比大于100的Bi2Te3纳米线.XRD和TEM分析表明,随着溶剂介电常数和极性增加,所生成产物的物相纯度、结晶度增高,晶粒尺寸增大.     

细晶Bi2Te3块体材料的制备及其热电性能

采用惰性气体保护蒸发-冷凝(IGC)法制备了纳米Bi及Te粉末,结合机械合金化(MA)和放电等离子烧结(SPS)工艺,在不同烧结温度(663～723K)下制备出了n型Bi2Te3细晶块体材料。利用X射线衍射分析(XRD)确定机械合金化粉末和SPS烧结块体的物相组成,借助TEM观察了粉体的粒度及形貌,SEM观察了块体试样断口显微组织结构。在323～473K温度范围内测试了烧结块体的电热输运特性。实验结果表明:纳米粉末合成的细晶Bi2Te3与粗晶材料相比,电输运性能变化不大,热导率大幅度降低,在423K时,热导率由粗晶材料的1.93W/m·K降至1.29W/m·K,并且在693K烧结的细晶块体的无量纲热电优值(ZT)在423K时取得最高ZT值达到0.68。     

纳米SiC分散的Bi2Te3热电材料的制备与性能研究

用机械合金化工艺（MA）和放电等离子烧结工艺（SPS），制备出纳米SiC（平均直径约30nm）弥散分布的Bi2Te3热电材料，并研究了纳米SiC颗粒弥散对Bi2Te3性能的影响。实验采用MA合成纳米SiC分散Bi2Te3粉末，用SPS制备块体材料。XRD分析表明用MA和SPS成功制备了Bi2Te3合金，随着纳米SiC含量的增加，材料的颗粒尺寸减小，表明纳米SiC有抑制颗粒长大的作用。电学性能测试发现少量（体积分数≤1．0％）纳米SiC的加入对Bi2Te3电学性能有很大影响：虽然随着SiC含量的增加电导率有所降低，但Seebeck系数得到了提高。当加入0．1％SiC时，Seebeck系数和功率因子达到最大值，均高于纯Bi2Te3试样，随着SiC含量进一步增加，Seebeck系数和功率因子降低。显微硬度随着纳米SiC含量的增加也得到提高。综合实验结果表明极少量纳米SiC颗粒的加入可以提高Bi2Te3的电学性能和力学性能。     

额外Te的掺杂量对P型碲化铋基合金热电性能的影响

采用区熔法制备了P型（Bi0.15Sb0.85）2Te3＋x％Te（z=0-6）热电材料，利用电子探针（EPMA）观察了区熔材料的显微结构并进行了物相分析，在300～500K的温度范围内分别测量了材料的塞贝克系数α、电导率σ以及热导率κ。结果表明：随着额外Te的含量增加，材料的载流子（空穴）浓度减小，电导率降低；同时，载流子对声子的散射作用减弱，但第二相的存在对声子的散射作用增强，二者的共同作用使晶格热导率在室温附近随着Te含量先减小而后增大。材料的性能优值ZT则随Te含量先增大后减小，当额外Te的质量分数为3％时具有最大的ZT值，约为0．92。     

Thermoelectric properties for P-type (Bi2Te3)0.2(Sb2Te3)0.8 alloys fabricated by shear extrusion

P-type (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 compounds were synthesized via bulk mechanical alloying (BMA), and subsequently prepared by a shear extrusion process in order to create the developed texture. The shear extrusion process improved the preferred orientation factor of the anisotropic crystallographic structure. It was found by an electron backscattered diffraction pattern (EBSP) analysis that approximately 90% of the crystallographic orientations for shear-extruded sample are aligned in the range deviated from 60° to 90° from the c-axis. The electric resistivity is well controlled at 1.008×10⁻⁵Ωm, which is nearly equal to that of the unidirectionally grown sample. The maximum figure of merit for the (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 alloy was found to be z=3.03×10⁻³K⁻¹. The bending strength of the material produced is also improved to 120 MPa, six times larger than that of the unidirectionally grown sample.     

溶剂热合成Bi2Te3基合金的结构与电学性能

用溶剂热法合成了二元Bi2Te3和三元Bi1.3Sn0.7Te3合金纳米粉末,并采用热压技术制备了块状热电材料.XRD分析结果表明:Bi-Sn-Te三元固溶体合金可以直接通过溶剂热合成获得单相产物,而非掺杂Bi2Te3合金需要通过热压等后热处理来实现产物的单一化;热压过程有助于促进反应的完全和晶型的完整,但会导致晶粒的长大.对试样电导率σ和Seebeck系数α的测量结果显示,Bi-Sn-Te三元固溶体合金比二元Bi-Te合金具有更好的电学性能.     

Thermoelectric properties of p-type (Bi2Te3)x(Sb2Te3)1−x prepared by spark plasma sintering

High performance (Bi₂Te₃)_x(Sb₂Te₃)_1?x bulk materials have been prepared by combining fusion technique with spark plasma sintering, and their thermoelectric properties have been investigated. With the increase of Bi₂Te₃ content, the electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases signi?cantly, which lead to a great improvement in the thermoelectric ?gure of merit ZT. The maximum ZT value reaches 1.33 at 398 K for the composition of 20% Bi₂Te₃–80%Sb₂Te₃ with 3 wt% excess Te.     

Effect of powder mixing on thermoelectric properties in Bi2Te3-based sintered compounds

The effect of powder mixing on thermoelectric properties was studied in n-type Bi₂Te_2.85Se_0.15 compounds and p-type Bi_0.5Sb_1.5Te₃ compounds. The figure-of-merit of the n- and p-type sintered compounds was strongly affected by carrier mobility. The use of coarse powders (200–300 μm) was beneficial to improve the crystallographic orientation of sintered compound. However, voids in the compound decreased the carrier mobility. As the fine powders (below 45 μm) were blended with coarse powders up to about 30%, the carrier mobility was increased due to the reduction of the voids. The addition of fine powders over 30% degraded the carrier mobility due to the decrease of crystallographic orientation and the increase of particle boundary. When the fine powder content was 20%, the n- and p-type compounds exhibited the maximum figure-of-merit of 2.31 × 10⁻³ K⁻¹ and 2.89 × 10⁻³ K⁻¹, respectively.     

Diffusion Soldering of Bi0.5Sb1.5Te3 Thermoelectric Material with Cu Electrode

For the production of thermoelectric modules, Bi_0.5Sb_1.5Te₃ was sequentially electroplated with a 4-μm Ni barrier layer and a 10-μm Ag layer and then diffusion soldered with the Cu electrode, which was also electroplated with 4-μm Ag and 4-μm Sn layers. The Bi_0.5Sb_1.5Te₃ and Ni interface with no sufficient chemical bonds resulted in a bonding strength lower than 3 MPa. Through the pre-coating of a 1-μm Sn thin film on Bi_0.5Sb_1.5Te₃ and heating at 250 °C for 3 min before the electroplating of the Ni barrier layer, the bonding strengths of Bi_0.5Sb_1.5Te₃/Cu assemblies increased to a maximal value of 10.7 MPa. The intermetallic compounds formed at various interfaces in the Bi_0.5Sb_1.5Te₃/Cu modules after diffusion soldering at temperatures ranging from 250 to 325 °C for 5-60 min and their growth kinetics was analyzed.     

无机有机复合材料Bi2Te3／PAn电化学嵌锂性能研究

采用机械共混法制备了复合材料Bi2Te3/PAn,并对其电化学嵌锂性能进行了研究.研究发现Bi2Te3/PAn快速充放电性能良好,在以100 mA·g-1的电流密度充放电时首次可逆容量为480 mAh·g-1,到第20个循环时容量保持在200mAh·g-1.通过非原位X射线衍射方法研究其嵌锂机理,发现Bi2Te3在首次放电时分解,在随后的循环中以Te和Bi为嵌锂中心进行可逆储锂.     

H2V3O8 single-crystal nanobelts: Hydrothermal preparation and formation mechanism

The formation mechanism of highly pure H₂V₃O₈ single-crystal nanobelts is clarified in a hydrothermal synthesis process with a specially designed precursor solution containing V⁵⁺ and V⁴⁺ in a fixed ratio of 2/1. This specially designed precursor solution provides an additional merit for the rapid fabrication of highly pure H₂V₃O₈ nanobelts through a simple hydrothermal route. During the hydrothermal synthesis process, V⁵⁺ species initially reacts with some V⁴⁺ to form a metastable, whisker-like V₁₀O₂₄ · nH₂O (n < 12). The V⁵⁺ species dissolved from the whisker-like V₁₀O₂₄ · nH₂O reacts continuously with residual V⁴⁺ ions in the precursor solution to form seeds of H₂V₃O₈ single-crystals. The anisotropic growth of H₂V₃O₈ single-crystal nanobelts with length > 10 μm and width between 50 and 150 nm occurs with prolonging the hydrothermal time. Finally, highly pure H₂V₃O₈ single-crystal nanobelts are obtained when the hydrothermal time reaches 4 h. The textures of vanadium oxides prepared at different hydrothermal times are systematically compared through X-ray diffraction, transmission electron microscopic and X-ray photoelectron spectroscopic analyses to clarify the synthesis mechanism of H₂V₃O₈ single-crystal nanobelts.     

Thermoelectric properties of the hot-pressed Bi2(Te0.85Se0.15)3 alloy with addition of BN powders

Thermoelectric properties of the hot-pressed Bi₂(Te_0.85Se_0.15)₃ alloy were investigated with the addition of BN powders as phonon scattering centers. The Seebeck coefficient and electrical resistivity of the alloy increased as the volume fraction of BN increased. Although the thermal conductivity of the alloy decreased as the volume fraction of BN increased due to the reduction of K_el, the lattice thermal conductivity varied little. The figure-of-merit of the alloys, 1.6×l0^-3/K without the addition of BN, decreased as the volume fraction of BN increased because the increment of the electrical resistivity was much larger than the decrement of the thermal conductivity due to grain refinement.     

Enhanced performances of melt spun Bi2(Te,Se)3 for n-type thermoelectric legs

In this article, a rapid and cost-effective melt spinning (MS) subsequently combined with a spark plasma sintering (SPS) process was utilized to prepared n-type Bi₂(Te_1?xSe_x)₃ (x = 0.0–1.0) solid solutions from high purity single elemental chunks. The substitution of tellurium by selenium has significant impacts on the electrical and thermal transport properties of the Bi₂(Se_xTe_1?x)₃ compounds in a manner which can be well understood using a valence bond rule and the corresponding change in band gap. Furthermore, the selenium substitution effectively adjusts the carrier density allowing an optimum value of ～5 × 10^?19 cm^?3. As a result, a maximum ZT of 1.05 at 420 K was achieved for the Bi₂(Se_0.2Te_0.8)₃ sample which also shows an improved average ZT of ～0.97 in the entire measurement temperature range. By adopting the same p-type legs, the module fabricated by the MS-SPS Bi₂(Se_0.2Te_0.8)₃ material which acts as n-type legs shows ～10% enhancement in thermoelectric conversion efficiency compared with the module fabricated by n-type zone melted ingots.