Na/Se掺杂p-型AgSbTe2化合物热电性能研究

采用熔融-淬火-放电等离子烧结方法制备了两种不同掺杂方式的Na单掺和Na/Se共掺p型AgSbTe2多晶块体材料(Ⅰ:掺杂元素以过量形式添加AgNa0.01SbTe2,AgNa0.01SbTe2Se0.04;Ⅱ:掺杂元素以置换对应元素形式添加Ag0.99Na0.01SbTe2,Ag0.99Na0.01SbTe1.96Se0.04).研究了Na单掺、Na/Se共掺及不同掺杂方式对材料电、热输运性能的影响规律.通过比较不同掺杂方式样品的电、热传输性能确定了最佳的Na/Se掺杂方式:Na置换Ag,Se置换Te并结合适当的Se过量加入.由于Na掺杂对Seebeck系数的提高及Se掺杂对电导率和热导率的优化,Ag0.99Na0.01SbTe1.96Se0.04化合物ZT最大值在620 K达到1.4,较未掺杂AgSbTe2化合物提高约17%.     

NaxCo2O4基复合材料的制备及其热电性能

采用固相反应法制备出NaxCo2O4(x=0.9,1.1,1.3)多晶氧化物,采用水热法制备出(Bi0.1Sb0.9)2Te3单相粉末材料,再用球磨法将二者均匀混合获得了复合材料(Bi0.1Sb0.9)2Te3/NaxCo2O4。在5～300K的温度范围内,利用综合物性测试系统(PPMS)对热压复合材料的热电性能进行测量与评价。实验结果表明复合材料的热导率显著降低,同时电导率增大,与NaxCo2O4相比,复合材料的热电性能获得了显著提高。在室温下,复合材料的热电优值ZT约为3.5×10-4。热电性能的改善源于复合材料界面的声子散射的增强。     

p型多晶Bi0.5Sb1.5Te3合金类施主效应与热电性能

晶粒细化是提高Bi_0.5Sb_1.5Te₃合金力学性能的有效途径,但是粉末冶金过程中晶粒细化导致的类施主效应会严重劣化材料热电性能,制约了Bi_0.5Sb_1.5Te₃基合金在微型热电器件中的应用。本研究围绕p型Bi_0.5Sb_1.5Te₃基合金,采用实验结合理论计算系统研究了粉末冶金制备过程中研磨和脱附气氛对烧结样品中类施主效应和电热输运性能的影响规律和机制。Bi_0.5Sb_1.5Te₃基合金破碎研磨过程中粉体表面产生缺陷V_Te^··和V_S’’_b并物理吸附空气中的O₂,在烧结过程中与吸附的O₂发生缺陷化学反应,产生大量V_Te^··空位和自由电子,导致类施主效应,使空...     

Ag-Bi-Sb-Te四元合金的热电性能

以Ag、Bi、Sb、Te为原料在1373K真空熔炼合成了AgxBi0.5Sb1.5-xTe3(x=0～0.5)合金.微观组织和结构分析显示,真空熔炼的合金具有层状组织特征,属R3m晶体结构,当x≥0.2时出现面心立方AgSbTe2相.电学性能测试表明,在300～580K温度范围内合金的电导率随温度升高而下降,掺Ag后合金的电导率明显提高,掺Ag量为x=0.1试样的最大值达到2.3×105S/m.材料的Seebeck系数均为正值,表明掺Ag合金为p型半导体.     

(Mg2Si1-xSbx)0.4-（Mg2Sn）0.6固溶体合金的制备及热电输运特性

以Mg、Si、Sn、Sb块体为原料,采用熔炼结合放电等离子烧结(SPS)技术制备了n型(Mg2Si1-xSbx)0.4-(Mg2Sn)0.6(0≤x≤0.0625)系列固溶体合金.结构及热电输运特性分析结果表明:当Mg原料过量8wt%时,可以弥补熔炼过程中Mg的挥发损失,形成单相(Mg2Si1-xSbx)0.4-(Mg2Sn)0.6固溶体.烧结样品的晶胞随Sb掺杂量的增加而增大;电阻率随Sb掺杂量的增加先减小后增大,当样品中Sb掺杂量x≤0.025时,样品电阻率呈现出半导体输运特性,Sb掺杂量x>0.025时,样品电阻率呈现为金属输运特性.Seebeck系数的绝对值随Sb掺杂量的增加先减小后增大;热导率κ在Sb掺杂量x≤0.025时比未掺杂Sb样品的热导率低,在Sb掺杂量x>0.025时高于未掺杂样品的热导率,但所有样品的晶格热导率明显低于未掺杂样品的晶格热导率.实验结果表明Sb的掺杂有利于降低晶格热导率和电阻率,提高中温区Seebeck系数绝对值;其中(Mg2Si0.95Sb0.05)0.4-(Mg2Sn)0.6合金具有最大ZT值,并在723 K附近取得最大值约为1.22.     

一维Bi2Te3基纳米材料的制备、结构控制与热电性能

热电材料的低维化可以改善材料电输运与热传输的矛盾,特别是一维纳米热电材料明显的晶体各向异性和强烈的量子禁闭效应,可大幅度提高材料的热电优值和热电转换效率。Bi2Te3是制造低温热电材料的最常用材料,在温差发电和半导体制冷方面具有广阔的商业应用前景。以一维Bi2Te3基纳米热电材料的制备技术为评述线索,重点论述一维Bi2Te3基纳米热电材料形貌参数(包括直径、长径比)、晶面取向等微观结构的调控方法、生长机理以及显微结构对热电性能的影响规律。指出发展新的一维Bi2Te3基纳米热电材料结构控制方法,研究一维纳米热电材料的定向排布及组装技术,从更深层次揭示一维结构与热电性能的关系,以及开发一维Bi2Te3基纳米热电材料在各领域的实际应用是未来研究的发展方向。     

高压制备多晶Te掺杂Bi2Se3热电材料性能的研究

该文采用高温高压法合成了多晶Bi₂Se_3-yTe_y(y=0.1,0.3,0.5)样品。XRD对所有样品的物相分析表明,合成压力1GPa时获得的样品均为Bi₂Se₃基纯相样品。随后测试的所有样品的Seebeck系数均为负值,表现出典型的n型导电特性。热电参数测试结果表明Bi₂Se_2.5Te_0.5样品具有较优的热电性能,Seebeck系数绝对值和功率因子在567K附近分别达到最大值90.5μVK^-1和783.2μWm^-1K²。同时,在整个测试温度范围内热导率随温度的升高而降低,最小值为1.76W/mK。最终,Bi₂Se_2.5Te_0.5样品的无量纲优值ZT在567K附近达到最大值0.25。     

Bi2Te3与SnBi2Te4的电子结构与热电性能研究

用离散变分密度泛函分子轨道方法(DFT-DVM)和线性扩展平面波能带方法(LAPW)计算了Bi2Te3与SnBi2Te4,讨论了电子结构与热电性能之间的关系.Te(Ⅱ)-Bi离子键强度和Te(Ⅰ)-Bi差别不大,而Te(Ⅱ)-Bi共价键比Te(Ⅰ)-Bi强.Te(Ⅰ)-Te(Ⅰ)原子层之间的主要相互作用是范得华力而最弱.Bi2Te3掺Sn后Te-Bi离子键增强而共价键减弱,且费米能级处带隙变小.Sn主要影响导带结构.     

高度织构NaCo2O4陶瓷的热电性能研究

结合固相反应法和冷高压成型技术制备了具有高度结晶各向异性的热电氧化物陶瓷NaCo2O4．X射线衍射和扫描电子显微镜测试表明冷高压压制成型后烧结有利于样品内层状晶粒的C轴沿着施压方向取向排列，形成高度织构．室温以下热电性质的测试表明，电阻率P和Seebeck系数S呈现出金属性，S〉0，属于p型热电材料．与其他方法制备的样品进行比较，虽然晶界或点缺陷对声子散射的减少导致上述样品的热导率偏高，但是由于ρ降低、S升高，使得热电品质因子ZT值提高，300K时ZT值达到0．013．     

SrAl2合金的储氢动力学性能

研究了在Zintl相SrAl2合金中添加不同金属氯化物催化剂后的相结构和吸氢动力学性能。XRD分析表明,合金吸氢前仍然为SrAl2相,催化剂由于含量较少未被检测出;吸氢后,合金相结构根据催化剂添加种类的不同分为以下两种情况:氢化程度高的样品,由SrAl2H2、SrAl4和SrH2三相组成;氢化程度低的样品,由SrAl2H2、SrAl4、SrH2和未反应的SrAl2四个相组成。储氢性能研究表明,添加金属氯化物催化剂能够有效改善SrAl2合金的吸氢动力学性能。吸氢动力学机理分析表明,SrAl2合金吸氢控制步骤为表面化学反应,而添加催化剂使得合金的吸氢控制步骤转变为三维扩散。     

Optical constants of polycrystalline CuGaTe2 films

Thin films of CuGaTe₂ with thicknesses in the range, 0.1–1.0 μm were deposited on Corning 7059 glass substrates by flash evaporation. The substrate temperatures, T_s, were maintained in the range 373–623 K. The transmittance of the films was recorded in the wavelength range 900–2500 nm. The dependence of the optical band gap, E_g, on substrate temperature showed that the value of E_g varied from 1.21 eV to 1.24 eV. The variation of refractive index and extinction coefficient with photon energy was studied from which the material properties such as the limiting value of dielectric constant, ε_∞, plasma frequency, ω_p, and hole effective mass, m_h^*, were evaluated as ε_∞ = 7.59, ω_p = 1.47 × 10¹⁴ and m_h^* = 1.25 m₀.     

Thermoelectric properties of Zn doped Cu2SnSe3

Zn doped ternary compounds Cu₂Zn_xSn_1−xSe₃ (x = 0, 0.025, 0.05, 0.075) were prepared by solid state synthesis. The undoped compound showed a monoclinic crystal structure as a major phase, while the doped compounds showed a cubic crystal structure confirmed by powder XRD (X-Ray Diffraction). The surface morphology and elemental composition analysis for all the samples were studied by SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Micro Analyzer), respectively. SEM micrographs of the hot pressed samples showed the presence of continuous and homogeneous grains confirming sufficient densification. Elemental composition of all the samples revealed an off-stoichiometry, which was determined by EPMA. Transport properties were measured between 324 K and 773 K. The electrical resistivity decreased up to the samples with Zn content x = 0.05 in Cu₂Zn_xSn_1−xSe₃, and slightly increased in the sample Cu₂Zn_0.075Sn_0.925Se₃. This behavior is consistent with the changes in the carrier concentration confirmed by room temperature Hall coefficient data. Temperature dependent electrical resistivity of all samples showed heavily doped semiconductor behavior. All the samples exhibit positive Seebeck coefficient (S) and Hall coefficient indicating that the majority of the carriers are holes. A linear increase in Seebeck coefficient with increase in temperature indicates the degenerate semiconductor behavior. The total thermal conductivity of the doped samples increased with a higher amount of doping, due to the increase in the carrier contribution. The total and lattice thermal conductivity of all samples showed 1/T dependence, which points toward the dominance of phonon scattering at high temperatures. The maximum 1/TZT = 0.48 at 773 K was obtained for the sample Cu₂SnSe₃ due to a low thermal conductivity compared to the doped samples.     

Analysis of the edge emission of highly conductive CuGaTe2

Low temperature photoluminescence of CuGaTe₂ was studied using number of different samples. Totally 11 photoluminescence bands were detected in the edge emission region. It is shown that at least 6 bands have peak positions at higher energy than the lowest optical bandgap of CuGaTe₂. These bands were explained by using a model of resonant acceptor states (Fano-type resonances) in the valence band of CuGaTe₂. Thus, the electron from the conduction band or from the donor level recombines with holes from acceptor levels related to the different valence bands. The energetic distance between these valence bands is found to be 84 meV.     

Structural characterization and novel optical properties of defect chalcopyrite ZnGa2Te4 thin films

Stoichiometric thin film samples of the ternary ZnGa₂Te₄ defect chalcopyrite compound were prepared and characterized by X-ray diffraction technique. The elemental chemical composition of the prepared bulk material as well as of the as-deposited film was determined by energy-dispersive X-ray spectrometry. ZnGa₂Te₄ thin films were deposited, by conventional thermal evaporation technique onto highly cleaned glass substrates. The X-ray and electron diffraction studies revealed that the as-deposited and the annealed ZnGa₂Te₄ films at annealing temperature t_a ≤ 548 K are amorphous, while those annealed at t_a ≥ 573 K (for 1 h), are polycrystalline. The optical properties of the as-deposited films have been investigated for the first time at normal incidence in the spectral range from 500 to 2500 nm. The refractive index dispersion in the transmission and low absorption region is adequately described by the Wemple–DiDomenico single oscillator model, whereby, the values of the oscillator parameters have been calculated. The analysis of the optical absorption coefficient revealed an in-direct optical transition with energy of 1.33 eV for the as-deposited sample. This work suggested that ZnGa₂Te₄ is a good candidate in solar cell devices as an absorbing layer.     

AgSbTe_2热电化合物的超声化学法合成

采用超声化学法结合还原热处理合成了单相的AgSbTe2粉体,并结合放电等离子烧结(SPS)制备了相应的块体.系统研究了不同前驱体制备条件、热处理温度、时间和起始化学计量比对相组成的影响,并对烧结块体的热电性能进行了初步研究.结果表明:超声化学法合成的前驱体在500℃、2h还原热处理后可以得到近单相的AgSbTe2,且通过调节起始原料的摩尔比可以得到单相的AgSbTe2.所得粉体颗粒平均粒径约为10μm,表面均匀分布着20~50nm的纳米颗粒.性能测试表明单相样品的无量纲热电优值ZT值在570K最大可达1.14.     

Photoelectrochemical properties of Re6Se8Cl2 a lamellar transition metal cluster compound

Photoelectrochemical properties of vapor-grown single crystals Re₆Se₈Cl₂ are presented; this Re₆Se₈Cl₂ is a n-type semiconductor with a direct bandgap of about 1.42eV, corresponding to a probable d-d phototransition. The material is not stable under prolonged illumination in aqueous acidic and basic solutions. Addition of a I^?/I^?₃ redox system in acidic solution increases the photopotential (very strongly) to 490mV, shifts 600mV cathodically the onset of the anodic photocurrent and improves considerably the stability of the Re₆Se₈Cl₂ photoanode. This behavior is analysed in relation to the d band semiconductor character of Re₆Se₈Cl₂.     

Crystal structure and magnetic properties of the compound FeDy6Sb2

The crystal structure of a compound FeDy₆Sb₂ was determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the hexagonal, space group P6¯2m (No. 189) with the Fe₂P structure type and lattice parameters a = 0.81449(5) nm, c = 0.41641(3) nm, z = 1 and D_calc = 8.842 g/cm³. The maximum magnetic entropy change ΔS_M for the compound is 3.41 J kg^− 1 K^− 1 near its Curie temperature (143.4 K) on the magnetic field changes of 0-2.0 T.     

Thermoelectric properties of Zn4Sb3 prepared by hot pressing

Polycrystalline specimens of the thermoelectric material Zn₄Sb₃ were prepared by the hot-pressing method at various temperatures and pressures and their thermoelectric properties were evaluated in a temperature range from 298 K to 673 K. A single phase of Zn₄Sb₃ was obtained in the samples prepared at 673 K with a pressure above 150 MPa, whereas ZnSb was placed in the Zn₄Sb₃ matrix for the samples prepared at 100 MPa. The electrical transport properties of the single phase compound showed p-type conduction and metallic transport behavior based on the temperature dependence. The sample produced at 673 K under a pressure of 200 MPa exhibited the highest ZT value of 1.36 at 673 K. This study suggests that the dense and single-phase Zn₄Sb₃ compound is a route to achieve a high thermoelectric performance.     

On the ternary compound TlSbS2 and its photoelectric properties

The Tl₂S /1b Sb₂S₃ phase diagram was examined and three ternary compounds, Tl₃SbS₃, TlSbS₂ and TlSb₅S₈ were found. The electrical and photoelectrical properties of TlSbS₂ crystals and evaporated thin films were investigated.