Effects of high-pressure high-temperature treatment on the thermoelectric properties of PbTe

Changes in the thermoelectric properties of nominally undoped stoichiometric PbTe caused by high-pressure high-temperature (HPHT) treatment near 6.5 GPa and 900 °C are reported. Comparison of the electrical resistivity, thermopower, and thermal conductivity suggest that the carrier concentration and lattice defect density are decreased by HPHT treatment. Annealing the treated samples at intermediate temperatures (500–600 °C) reversed the changes. These observations are consistent with Pb vacancies being “squeezed out” by the applied pressure, and subsequently reintroduced by annealing.     

Composition-dependent thermoelectric properties of PbTe doped with Bi2Te3

The composition-dependent thermoelectric properties of PbTe doped with Bi₂Te₃ have been studied at room-temperature. The electrical resistivity and the Seebeck coefficient in absolute value decrease with an increase of Bi₂Te₃. A sharp maximum in the Seebeck coefficient at 0.3 mol% Bi₂Te₃ indicates that an electronic topological transition is occurred in PbTe alloyed with Bi₂Te₃. The total thermal conductivity nearly keeps constant and the parts of lattice, which are much lower than those doped with PbI₂ prepared by hot-pressing, linearly decrease with increasing Bi₂Te₃. The figure of merit shows a maximum value of 7.63 × 10⁻⁴ K⁻¹, which is several times higher than that of PbTe containing other dopants. The high thermoelectric performance is explained by electronic topological transition induced by alloying.     

Solubility of Ti in thermoelectric PbTe compound

For the first time, the temperature dependence of the solubility of Ti in PbTe is considered. The potential of Ti doping in PbTe was recently examined both theoretically and experimentally, in which a ∼9% efficiency enhancement was observed compared to an undoped PbTe. We present an experimental study of the system for different Ti concentrations indicating the solubility limit of Ti in PbTe and the effect of temperature on the morphology of the alloy. Exceeding the solubility limit leads to phase separation accompanied by formation of the TiTe₂ phase. At high temperatures, dissolution of the TiTe₂ secondary phase occurs for low Ti concentration, and the system transfers to the single-phase disordered solid solution. On the contrary, for the same temperatures, in the case of higher Ti concentrations the two-phase state is preserved. Theoretical explanation of the observed results is given using ab inito calculations combined with the statistical thermodynamic approach. The quasi-binary PbTe-TiTe₂ cross-section of the ternary Pb–Ti–Te phase diagram, indicating the Ti solubility in (Pb_1-cTi_c)Te is presented.     

Structure and magnetic properties of Pr0. 1CexTb0.9-xFe1.9 alloys

1　INTRODUCTIONTerfenol D ( Tb0.27 Dy0.73 Fe2 ) exhibits largemagentostriction and minimized magnetic anisotro py at room temperature[1], so it is widely used inactuators and transducers. But the main raw mate rials of Terfenol D are expensive Tb and Dy. Ac cording to the single ion model[2], CeFe2 and PrFe2compounds have larger magnetostriction thanTbFe2 and DyFe2 at 0 K. In addition, Ce and Prare much cheaper than Tb and Dy. So Ce basedand Pr based compo…     

First-principle calculations of the electronic,elastic and thermoelectric properties of Ag doped CuGaTe2

To improve the performance of a thermoelectric material CuGaTe₂, element Ag is doped to replace element Ga and we investigate the electronic structure, phase stability, elastic and thermoelectric properties of CuGa_1−xAg_xTe₂ (x = 0, 0.25 and 0.5) via first-principles method. The phase stability of CuGa_1−xAg_xTe₂ is discussed by analyzing the formation energy, cohesive energy and elastic constants. The calculated sound velocities decrease with the increase of Ag content, which is favorable for reducing the lattice thermal conductivity. The analysis of band structures shows that the replacement of Ga by Ag makes CuGaTe₂ undergo a direct-indirect semiconductor transition. The Ag doping induces steep density of states in valence band edge, which is beneficial for increasing the carrier concentration and improving thermoelectric performance of CuGaTe₂.     

Non-calcining process for CuAlO2 and CuAl0.9Ca0.1O2 ceramics

Synthesis of CuAlO₂ and CuAl_0.9Ca_0.1O₂ ceramics for thermoelectric application using a reaction-sintering process was investigated in this study. Without any calcination involved, the mixture of raw materials was pressed and sintered directly. Some peaks of remained Al₂O₃ were detected in CuAlO₂. CaAl₄O₇ and CuO were detected in CuAl_0.9Ca_0.1O₂. Density values 2.83–3.04 g/cm³ were found in CuAlO₂ pellets sintered at 1350 °C. In CuAl_0.9Ca_0.1O₂ ceramics, density values 3.10–3.31 g/cm³ were found in pellets sintered at 1350 °C. Thin polygonal grains were observed in CuAl_0.9Ca_0.1O₂. The reaction-sintering process has proven a simple and effective method in preparing CuAlO₂ and CuAl_0.9Ca_0.1O₂ ceramics for thermoelectric application.     

La2Mg0.9Al0.1Ni7.5-xCo1.5Mnx贮氢合金的相结构和电化学性能

研究了Mn替代Ni对La2Mg0.9Al0.1Ni7.5-xCo1.5Mnx(x=0,0.3,0.6,0.9)贮氢合金相结构和电化学性能的影响。XRDRietveld全谱拟合分析表明:Mn替代改变了合金的物相组成和物相的丰度。LaNi3相消失,αLa2Ni7相丰度的变化表现为先增加(x=0,0.3)后减少(x=0.6,0.9),LaMgNi4相和La5Ni19相的丰度则随合金中Mn含量x的增加而增加。Mn替代Ni降低了合金的贮氢容量、最大电化学放电容量和活化性能,La2Mg0.9Al0.1Ni7.2Co1.5Mn0.3合金电极表现出最好的电化学循环稳定性,合金的高倍率放电性能随Mn含量的增加降低,这归因于交换电流密度(I0)和氢扩散系数(D)的降低。     

Zr0.9Ti0.1V2合金循环吸放氢稳定性

研究了Zr0.9Ti0.1V2合金的循环吸放氢性能。合金在吸氢P-C-T曲线的特征区域内具有良好的循环吸氢稳定性,在P-C-T曲线的吸氢平台区（H/A为0.5左右）、吸氢形成氢化物初始阶段（H/A为1~1.2）、吸氢形成氢化物中间阶段（H/A为1.4左右）吸放氢循环测试中,每组循环内合金的吸氢量差别非常小,循环吸氢稳定性很好。经过70次吸氢循环后,合金的吸氢量可以恢复到1.957 (H/A),合金的粉碎程度很低,表明合金具有良好的循环吸氢能力     

添加Ag、Sb对PbTe化合物组织与结构的影响

在不同冷却速度下制备几种不同成分的多元AgPbmSbTem 2(m=10、14、18)化合物并进行退火处理。粉末X射线衍射结果表明,AgPbmSbTem 2具有与PbTe相同的面心立方结构。微观组织分析表明,自熔融状态快速冷却制备的化合物中存在严重的成分偏析,晶界处有富Ag、Sb相存在;缓慢冷却试样中偏聚相较少;退火处理后,试样中的偏聚相消失。制备得到的AgPbmSbTe2 m化合物具有典型的枝晶结构。用内标法精确测定Ag-PbmSbTem 2的晶格常数,晶格常数随m值增大而单调增加;减少化合物中的Ag含量,晶格常数增大。     

纳米晶SmCo_(8.9)Si_(0.9)永磁合金相变特征及其磁性能变化研究

首次制备出具有高稳定性的Sm Co_(8.9)Si_(0.9)纳米晶合金,进而系统研究了亚稳相Sm Co_(8.9)Si_(0.9)的相变特征及相应的磁性能变化规律。发现添加元素Si可以有效提高过饱和固溶体亚稳相SmCo_(9.8)的稳定性,随着热处理温度的升高,SmCo_(8.9)Si_(0.9)纳米晶合金由SmCo_(9.8)(H)结构的单相转变为Sm_2Co_(17)(H)和Co(fcc)相,且伴随相变,矫顽力提高。其机理源于析出的细小Co相造成钉扎机制增强。进一步升高热处理温度,Sm_2Co_(17)(H)相转变为Sm_2Co_(17)(R)相,同时晶粒长大明显且晶粒尺寸分布不均匀,导致磁性能下降。     

Zn1+xSb二元体系的相形成和热电性能

在Zn?Sb二元相图固相线以下使Zn和Sb粉末反应并随炉冷却,合成一系列Zn1+xSb(x=0,0.05,0.1,0.15,0.25,0.3)材料,分析Zn–Sb相图中心区域的相形成和热电性能.在此过程中,非化学计量比的混合粉末结晶形成ZnSb和 β-Zn4Sb3相的组合.然后,将材料研磨并热压成致密的ZnSb/β-Z...     

Microstructure and thermoelectric properties of Bi_(1.9)Lu_(0.1)Te_3 compound

Effect of fabrication conditions on micros tructure and thermoelectric properties of the Bi_(1.9)Lu_(0.1)Te_3 compound was studied.Starting nanopowder with mean nanoparticle size of ～37 nm was synthesized by a microwave-solvothermal method.In order to prepare samples with various micro-grained structures,the synthesized nanopowder was compacted by two methods.The first method is cold isostatic pressing with further hightemperature annealing,while the second method is spark plasma sintering at various temperatures of process(653 and 683 K).It is found that mean grain size is equal to～290,～730 and ～1160 nm for cold isostatically pressed and spark plasma sintered at 653 and 683 K samples,respectively.The micro-grained sample with maximum mean grain size shows the best thermoelectric properties.This sample is structurally inhomogeneous and has the lowest thermal conductivity and the specific electrical resistivity.Maximum dimensionless figure of merit for this sample is equal to ～0.9 for temperature range of450-500 K.     

球磨改性处理对Ti0．9Zr0．1Mn1．5合金相结构及储氢性能的影响

系统研究了Ti0．9Zr0．1Mn1．5储氢合金经不同时间（t=0min，10min，30min，60min）球磨改性处理后对其相结构及储氢性能的影响。结构分析表明，Ti0．9Zr0．1Mn1．5合金在球磨改性处理前后均由单一的六方结构的C14型Laves相组成；随着球磨时间的延长，合金粉的平均粒度减小，并出现了部分团聚现象。储氢性能测试表明，铸态合金经4次吸放氢循环后活化，室温最大吸氢量和有效放氢量分别为209．3ml／g和157．6ml／g，放氢率为75．3％；随着球磨时间的延长，合金的活化性能得到改善，室温最大吸氢量和有效放氢量均先升后降，且都在球磨30min时达到相应最高值231．4ml／g和203．8ml／g，放氢率达到88．1％。由此可见，适当的球磨改性处理能有效地改善Ti0．9Zr0．1Mn1．5合金的综合储氢性能。     

Formation of Ag2S nanowires and Ag2S/CdS heterostructures via simple solvothermal route

In our present work, Ag₂S nanowires and Ag₂S/CdS heterostructures have been successfully prepared in anhydrous ethanol through a simple solvothermal route. From the transmission electron microscopy (TEM) analysis, it is found that the factors influenced the final product are the concentration of Ag⁺, reaction temperature, reaction time, and solvent. Ag₂S nanowires are formed by complete Ag⁺ cation exchange. Because of the selectivity for partial cation exchange, the reaction starts preferentially at the ends of the CdS nanowires to produce novel Ag₂S/CdS heterostructures. In addition, as the two end facets of wurtzite CdS nanowires are crystallographically nonequivalent, the produced Ag₂S/CdS heterostructures are asymmetric.     

Ca_3Co_4O_9/Ag陶瓷复合材料的制备及其热电性能

利用高分子网络凝胶法和放电等离子烧结技术(SPS)制备出高致密的Ca3Co4O9/Ag热电陶瓷复合材料.采用X射线衍射法表征了材料的相组成及其织构化程度,用SEM观察了粉体形貌和陶瓷断口的显微结构,并研究了Ag复合量对材料的室温热电性能的影响.研究结果表明,利用高分子网络凝胶法和SPS相结合的工艺有利于单质Ag在基体中的分布,使得基体中Ag相的粒径更小,分布更均匀.陶瓷复合材料的致密度均达到98%以上.虽然Ag颗粒的加入使Ca3Co4O9/Ag复合材料的Seebeck系数降低,但由于电导率显著提高,从而使材料的功率因子提高.     

快速凝固制备La2Mg0．9Ni7．5Co1．5Al0.1贮氢合金的相结构及电化学性能

采用感应熔铸＋退火处理及快速凝固方法制备了La2Mg0．9Ni7．5Co1．5Al0.1贮氢合金。系统研究了快速凝固对合金的相结构、微观组织及电化学性能的影响。XRD分析表明，随着冷却速率的增加，La2Mg0．9Ni7．5Co1．5Al0.1合金的相组成发生了明显变化。退火合金由αLa2Ni7主相（Ce2Ni7型结构）和少量LaNi3相（PuNi3型结构）组成。随着冷却速率的增加，合金中出现LaNi5相（CaCu5型结构）和LaMgNi4（MgCu4Sn型结构）相，且新相的相丰度增加，aLa2Ni7相和LaNi3相的丰度减少。EPMA分析表明，快速凝固方法制备的La2Mg0．9Ni7．5Co1．5Al0.1贮氢合金为柱状晶组织且晶粒细小。合金电极的电化学测试表明，冷却速率对合金的活化性能影响不大。随冷却速率的增加，合金的最大放电容量减少、高倍率放电性能下降。在较低的冷却速率下（5m／s），合金电极的循环稳定性改善不明显，而随着凝固速度的进一步增加（20m／s），合金电极表现出较好的循环稳定性。     

Directional thermoelectric properties of Ru2Si3

The orthorhombic compound Ru₂Si₃ is currently of interest as a high-temperature thermoelectric material. In order to clarify the effects of crystal orientation on the thermoelectric properties of Ru₂Si₃, we have examined the microstructure, Seebeck coefficient, electrical resistivity, and thermal conductivity of Ru₂Si₃ along the three principal axes, using these measured quantities to describe the relative thermoelectric performance as a property of crystal orientation. Ru₂Si₃ undergoes a high temperature (HT)→low temperature (LT) phase change and polycrystalline Si platelet precipitation during cooling, both of which are expected to effect the thermoelectric properties. The HT tetragonal→LT orthorhombic phase transformation results in a [010]//[010], [100]//[001] two-domain structure, while polycrystalline Si precipitation occurs on the (100)_LT and (001)_LT planes. The [010] orientation is found to posses superior thermoelectric properties (with the dimensionless figure of merit, ZT_[010]/ZT_[100]>4 at 900 K), due principally to the larger Seebeck coefficient along the [010] direction. The effect of the domain structure on the thermoelectric properties is discussed.     

Ag2S/rGO纳米复合材料的细菌还原制备及光电性能研究

以一种革兰氏阴性菌(S.oneidensis MR-1)为生物还原剂,Na2S2O3为电子受体,在氧化石墨烯(GO)表面原位合成了Ag2S/rGO纳米复合材料,对其进行了表征和光电性能测试.结果表明,细菌还原得到粒径约10 nm的Ag2S纳米粒子,均匀分布在还原氧化石墨烯(rGO)上;光电性能测试表明,与纯Ag2S相比...     

Effects of Ag doping on thermoelectric properties of Zn4Sb3 at low temperatures

The thermoelectric properties of Ag-doped compounds (Zn_1?xAg_x)₄Sb₃ (x = 0, 0.0025, 0.005, 0.01) have been studied at the temperatures from 15 to 300 K. The results indicate that low-temperature (T < 300 K) thermal conductivity of the moderately doped (Zn_1?xAg_x)₄Sb₃ (x = 0.0025 and 0.005) reduced remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient were found to increase first and then decrease obviously with the increase in the Ag content, which could be ascribed to the change of carrier concentration presumably due to different Zn positions occupied by Ag upon increasing doping content. Moreover, the lightly doped compound (Zn_0.995Ag_0.005)₄Sb₃ exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity, whose figure of merit (at 300 K), ZT, is about 1.3 times larger than that of β-Zn₄Sb₃ obtained in the present study. Present results suggest that proper Ag doping in Zn₄Sb₃ is a promising way of improving its thermoelectric properties.     

The electric and thermoelectric properties of CuInSe2-based chalcopyrite

It has been found that CuInSe₂ chalcopyrite is an extrinsic semiconductor that exhibits a more complex temperature dependence of its electric conductivity than conventional extrinsic semiconductors. This temperature dependence of the electric conductivity results from the complex structure of the electron energy spectrum in these crystals. The temperature dependence of the electric conductivity has been used to determine the activation energies of the energy levels of the intrinsic defects that are formed upon the violation of the stoichiometry of the CuInSe₂ structure. The analysis of the temperature dependence of the thermoelectric power has revealed that the main scattering mechanism at high temperatures is acoustic-phonon scattering.