Si对反应烧结SiC热电性能的影响

SiC是一种具有良好应用前景的高温热电半导体材料，近年来一直得到广泛的关注和研究。本文对反应烧结SiC的热电性能进行了初步研究，发现该材料中的Si对其热电性能有显著的影响。经研究发现，这一影响只有在一定温度和一定残留Si的情况下才能表现出来。     

掺杂对多晶热电材料SnSe影响的研究进展

综述了热电材料SnSe单晶和多晶的性能特点和研究进展。针对如何进一步提高多晶SnSe材料热电优值的问题,主要从提高功率因子、增强声子散射的角度,讨论了采用金属元素、卤素元素和稀土元素掺杂的方法来优化多晶SnSe材料的载流子浓度、降低热导率及提高电传输性能等。最后提出了通过掺杂工艺进一步提高SnSe热电性能可能遇到的挑战和需要注意的问题。     

SHS转炉补炉料的物相组成及显微结构特征

利用自蔓延高温合成(SHS)原理,选择工业铝粉作为发热剂,菱镁矿为供氧剂,通过铝热反应,研制出了一种以镁砂为骨料,以镁铝尖晶石和炭质材料作为结合相的新型SHS转炉补炉料.对不同环境温度下补炉料的物相组成及显微结构进行了研究,并对合成尖晶石的固相反应原理及SHS产物相的烧结机制进行了探讨.结果表明补炉料中颗粒状的骨料方镁石与SHS反应产物尖晶石、非晶质碳、少量刚玉相和硅酸盐玻璃相共同构成含有气孔的交织结构,形成尖晶石、碳桥和陶瓷相与方镁石骨料的多重结合;SHS反应过程分碳酸盐矿物的分解反应、铝热氧化还原反应(即SHS反应)和合成尖晶石的固相烧结反应三步进行,其烧结受扩散机理控制.     

离子交换法制备LDHs纳米复合材料及其影响因素研究

以层状双金属氢氧化物(LDHs)、氯化镁和氯化铝为原料,通过液相非稳态共沉淀法制备MgAl-Cl-LDHs溶胶,通过离子交换引入己基磺酸钠(SHS),制备SHS-LDHs纳米复合材料,研究了混合溶胶pH值、SHS的初始浓度、碳链长度以及LDHs的浓度对材料性能的影响。研究发现,当混合溶液的pH 7.25,LDHs的浓度不大于0.50%,且SHS的浓度高于20 mmol/L时,CH_3(CH_2)_5SO_3~-才能通过离子交换反应进入LDHs层间,得到SHS-LDHs纳米复合材料。     

内衬SHS陶瓷复合油管抗压性能有限元分析与试验研究

内衬SHS陶瓷使油管的抗防腐性能显著提高,但考虑到衬里管的性能与普通油管存在差异,本文选用抗压强度作为衡量管体性能的指标展开研究。采取有限元分析与试验研究相结合的方法对内衬SHS陶瓷复合油管的压溃过程进行分析与研究。掌握了油管压溃过程的破坏规律,得到陶瓷内衬管承载能力明显要高于普通油管,表现出较好的抗压性能。     

自烧结泥浆和涂料的研究

对高纯用Al2O3质泥桨采用SHS法和反应烧结法，使这种高耐火度并耐浸蚀的泥浆能在1300℃烧结并具有良好的结合性能。对同类型涂料进行的试验也取得了相同的结果     

自烧结泥浆和涂料的研究

对高纯Al2 O3质泥浆采用SHS法和反应烧结法 ,使这种高耐火度并耐浸蚀的泥浆能在1 30 0℃烧结并具有良好的结合性能。对同类型的涂料进行的试验也取得了相同的结果     

离子交换法制备LDHs纳米复合材料及其影响因素研究

以层状双金属氢氧化物(LDHs)、氯化镁和氯化铝为原料,通过液相非稳态共沉淀法制备MgAl-Cl-LDHs溶胶,通过离子交换引入己基磺酸钠(SHS),制备SHS-LDHs纳米复合材料,研究了混合溶胶pH值、SHS的初始浓度、碳链长度以及LDHs的浓度对材料性能的影响。研究发现,当混合溶液的pH 7.25,LDHs的浓度不大于0.50%,且SHS的浓度高于20 mmol/L时,CH_3(CH_2)_5SO_3^-才能通过离子交换反应进入LDHs层间,得到SHS-LDHs纳米复合材料。     

添加剂对SHS陶瓷内衬复合钢管性能影响的研究进展

概述了离心、重力分离自蔓延高温合成技术(SHS)的基本原理,总结了SHS技术中添加剂的分类及作用,从陶瓷层裂纹、致密度、耐腐蚀性及复合钢管结合强度四个方面论述了添加剂对复合钢管性能的影响,并对其发展前景进行了展望.     

自蔓延高温合成TiC/Fe金属陶瓷结构复合材料的研究

以C、Ti、Fe粉末为原料,采用自蔓延高温合成技术制备TiC/Fe金属陶瓷结构复合材料。笔者研究了稀土的加入及加入量对SHS反应组织形态影响的因素,预制块的压实度对SHS反应强烈程度的影响。实验结果表明:在SHS反应铸造方法合成的TiC/Fe复合材料表面的TiC颗粒呈理想孤立球状分布,Al_2O_3呈光亮的不规则形状。TiC/Fe表面复合材料结合紧密,从基体到复合层逐渐呈梯度过渡。稀土的加入使高温自蔓延反应组织晶粒得到细化,加入量过高,会抑制自蔓延反应的反应强度和剧烈程度,使表面复合层与基体结合疏松,结合厚度减小。TiC/Fe表面复合材料硬度远远高于基体,且从基体到复合层也呈现梯度分布。     

A novel nano-configuration for thermoelectrics: helicity induced thermal conductivity reduction in nanowires

In this article, we propose a novel helical nano-configuration towards the designing of high ZT thermoelectric materials. Non-equilibrium molecular dynamics (NEMD) simulations for 'model' bi-component nanowires indicate that a significant reduction in thermal conductivity, similar to that of flat superlattice nanostructures, can be achieved using a helical geometric configuration. The reduction is attributed to a plethora of transmissive and reflective phonon scattering events resulting from the steady alteration of phonon propagating direction that emerges from the continuous rotation of the helical interface. We also show that increasing the relative mass ratio of the two components lowers the phonon energy transmission at the interface due to differences in vibrational frequency spectra, thereby relatively 'easing' the phonon energy propagation along the helical pathway. While the proposed mechanisms result in a reduced lattice thermal conductivity, the continuous nature of the bi-component nanowire would not be expected to significantly reduce its electrical counterpart, as often occurs in superlattice/alloy nanostructures. Hence, we postulate that the helical configuration of atomic arrangement provides an attractive and general framework for improved thermoelectric material assemblies independent of the specific chemical composition.     

High temperature thermoelectric performance of p-type TaRhSn half Heusler compound: A computational assessment

Half Heusler compounds are gaining greater attractions as high temperature thermoelectric materials owing of their giant thermal power and promising thermoelectric performance. In the light of current study, we present a larger library having an overview of structural and physical details including electronic, mechanical, phonon and thermoelectric properties of TaRhSn material within the framework of the density functional theory and semi classical Boltzmann transport approach. The band structure calculations reveal the fact that TaRhSn is an indirect band gap semiconductor with energy gap of 1.25 eV. An in-depth insight on the thermoelectric properties such as the Seebeck coefficient, electrical conductivity, total thermal conductivity and figure of merit has been strictly put along with variation in temperature. The compound has the figure of merit with the maximum numeric value of 0.55 at 1100 K. The value of lattice thermal conductivity is found to be 19.4 W/mK at room temperature and shows a significant reduction in its value towards higher temperatures. These theoretical calculations have the capabilities to stimulate experimental research towards designing and improving the thermoelectric performance of TaRhSn based half Heusler compounds, thus permitting this compound as an efficient thermoelectric material at high temperatures.     

Efficient thermoelectric energy conversion on quasi-localized electron states in diameter modulated nanowires

It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases. Recently, we proposed that increase of the thermoelectric efficiency could be achieved by modulating the diameter of the nanowires. We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation. Moreover, it has been shown by another group that the phonon conductivity decreases in nanowires when they are modulated by dots. Here, the thermoelectric efficiency of diameter modulated nanowires is estimated, in the ballistic regime, by taking into account the electron and phonon transmission properties. It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion.     

Thermoelectric power of soft carbons between 4.2 and 280 K in relation to phonon drag effect

The thermoelectric power of soft carbons heat-treated to temperatures between 1700 and 3000°C was investigated between 4.2 and 280K. It was confirmed by X-ray and magnetoresistance measurements that the layer ordering was turbostratic for the samples heat-treated below 1900°C and it was graphitic for the samples heat-treated above 2100°C. The turbostratic specimens show a positive thermoelectric power which increases almost linearly with temperature. The graphitic specimens show a negative peak in the range between 20 and 35 K in the thermoelectric power versus temperature relationship. The temperature dependence of the thermoelectric power for these specimens can be classified into two distinct types in terms of heat treatment temperature. However, turbostratic specimens show no negative peak. The negative peak observed for graphitic specimens can be related to the phonon drag effect due to the coupling between carriers and long wave-length in-plane phonons, which is explained by the theory of phonon drag effect in graphite developed by Sugihara.     

Enhancement in thermoelectric properties using a P‐type and N‐type thin‐film device structure

In this study, we have fabricated thermoelectric devices with p‐type and n‐type conducting polymers and research the effect of device structure with the thermoelectric properties. It was found that the p‐type and n‐type structure greatly enhances the device's electrical conductivity due to separated charge carrier channels, but the Seebeck coefficient was reduced due to the increase of charge density by doping. Photoexcitation can improve the device's thermoelectric properties and can increase the Seebeck coefficient and electrical conductivity with increasing doping concentration simultaneously. The increases in both properties are due to the phonon–electron coupling effect: the concentration of electrons and holes are increased under illumination, and the phonon component of the heat flux can be reduced by phonon scattering. Consequently, the thermoelectric device structure can improve the efficiency of thermoelectric conversion. The P3HT:PCBM devices demonstrate a significant enhancement in the power factor (PF = S²σ), with a maximum value of ZT = 0.5 at 147°C, in which the PF value (34.8 μV/cm K²) is bigger than Bi₂Te₃/Sb₂Te₃ superlattice devices at room temperature. POLYM. COMPOS., 34:1728–1734, 2013. © 2013 Society of Plastics Engineers     

Enhanced thermoelectric performance in aluminum-doped zinc oxide by porous architecture and nanoinclusions

As a promising thermoelectric material, aluminum-doped zinc oxide (AZO) exhibits high thermal conductivity, which limits its use in high-temperature thermoelectric applications. Here, we report an effective route for forming a porous architecture and nanoinclusions by introducing nano-SiC to reduce the thermal conductivity. The simultaneous formation of a porous architecture and nanoinclusions promotes enhanced phonon scattering, resulting in fairly low thermal conductivity of approximately 3.3 W? m^?1? K^?1. Meanwhile, the Seebeck coefficient shows the significant improvement due to energy filtration effect caused by porous architecture and nanoinclusions. The resultant dimensionless figure of merit of approximately 0.2 at 1050 K was 1.5 times higher than that of AZO ceramic without nano-SiC, which is attributed to the combined factors of increased Seebeck coefficient and reduced thermal conductivity.     

Deformable thermoelectric sponge based on layer-by-layer self-assembled transition metal dichalcogenide nanosheets for powering electronic skin

In this study, we fabricated mechanically deformable thermoelectric sponges comprising transition metal dichalcogenides (TMDs) and polyethyleneimine (PEI) through a layer-by-layer (LBL) self-assembly technique for a thermoelectric power supply for electronic skin. Chemically exfoliated molybdenum sulfide (MoS₂) and niobium diselenide (NbSe₂) were prepared as p- and n-type room-temperature thermoelectric materials, respectively, and deposited on a melamine sponge via electrostatic bonding with PEI to obtain stable mechanical stretchability and low thermal conductivity. Five bilayers of LBL self-assembled thermoelectric sponges exhibited an enhanced thermoelectric performance and figure of merit, which resulted from the improvement in the Seebeck coefficient compared with that of pristine chemically exfoliated TMDs owing to the energy filtering effect and the extremely low thermal conductivity owing to the phonon scattering effect at several created interfaces and the porous structure of the sponge. Additionally, the thermoelectric sponges showed mechanical stability during operation under stretching and compression and mechanical durability over 10,000 cycles under 30% tensile strain. Finally, based on the proposed thermoelectric sponge, a power patch that can be installed on the back of a hand to produce electrical energy in real time was successfully demonstrated.     

Conductive scanning probe microscopy of nanostructured Bi2Te3

In order to explain the unique thermoelectric properties of bulk nanocomposite p-type bismuth antimony telluride, its structural and electrical properties are investigated using transmission electron microscopy (TEM) and atomic force microscopy with a conductive probe (C-AFM). The material is observed to contain both nano- and micro-sized grains with sizes varying from 10 nm to 3 μm. This unique structure promotes phonon scattering, thereby decreasing the thermal conductivity to below 1 W mK(-1) at room temperature. Moreover, the C-AFM data show that the electrical conductivity of nanosized grains is higher than the bulk value and reaches 1600 S cm(-1). This results in a moderate increment of the overall electrical conductivity, thereby increasing the figure of merit (ZT) up to 1.4 at 100 °C. In addition to demonstrating a powerful scanning probe microscopy (SPM) based investigation technique that requires minimal sample preparation, our findings contribute towards better understanding of the enhancement of thermoelectric properties of nanocomposite thermoelectric materials.     

Enhanced thermoelectric performances in BiCuSeO oxyselenides via Er and 3D modulation doping

BiCuSeO is a kind of promising oxide-based thermoelectric material with special natural superlattice structure. Herein, the effects of Er doping and modulation doping on the thermoelectric properties of BiCuSeO have been investigated. The results indicate that Er doping can tune the Fermi level, widen the band gap, reduce the energy offset between the heavy band and the light band, and then greatly improve the electrical conductivity, power factor and ZT. Modulation doping based on Er doping can increase carrier concentration and power factor significantly while maintaining high carrier mobility. Meanwhile, due to the special heterostructure of the modulation doping sample, the phonon scattering is greatly enhanced, and the corresponding lattice thermal conductivity is significantly reduced. Finally, the maximum ZT value reaches 0.99 for the modulation doped Bi_0.92Er_0.08CuSeO bulk at 873?K, which was ~1.8 times as that of the pristine BiCuSeO sample.     

Thermoelectric properties of small diameter carbon nanowires

The room temperature thermoelectric properties of three kinds of small diameter carbon nanowires are investigated by using nonequilibrium Green’s function method and molecular dynamics simulations. Due to very low thermal conductance and a relatively high power factor, these nanowires are found to exhibit better thermoelectric performance than other low-dimensional carbon-based materials such as carbon nanotubes. Moreover, the ZT values of these systems can be further increased to about 10 by partial passivation of hydrogen, which greatly reduces both the electron and phonon contributions to the thermal conductance, but leaves the power factor less affected.