快离子导体的低频介电特性

本文综述了快离子导体低频介电特性的实验规律,介绍和讨论了近年来提出的几个关于快离子导体介电特性的理论模型,并将实验结果与经验公式、理论模型进行了比较。     

RyMxCO4-xSb12化合物的晶格热导率

系统地研究了离子半径不同的Ba，Ce，Y作为填充原子及Fe，Ni作为置换原子对填充化合物RyMxCO4-xSb12晶格热导率的影响规律．结果表明：在skunemdite结构的sb组成的20面体空洞中，Ba，Ce，Y的填充原子能显著降低其晶格热导率，且晶格热导率降低幅度按Ba，Ce，Y离子半径减小的顺序而增大．Sb组成的20面体空洞部分被Ba，Ce填充时，晶格热导率最小，填充原子的扰动对声子的散射作用最强．在Co位置上Fe和Ni的置换，能显著地降低RyMxCO4-xSb12化合物的晶格热导率，与Fe相比，Ni对晶格热导率的影响更强．     

RyMxC04-xSb12化合物的晶格热导率

系统地研究了离子半径不同的Ba,Ce,Y作为填充原子及Fe,M作为置换原子对填充化合物RyMxCo4-xSb12晶格热导率的影响规律.结果表明在skutterudite结构的Sb组成的20面体空洞中,Ba,Ce,Y的填充原子能显著降低其晶格热导率,且晶格热导率降低幅度按Ba,Ce,Y离子半径减小的顺序而增大.Sb组成的20面体空洞部分被Ba,Ce填充时,晶格热导率最小,填充原子的扰动对声子的散射作用最强.在Co位置上Fe和M的置换,能显著地降低RyMxC2o4-xSb12化合物的晶格热导率,与Fe比,M对晶格热导率的影响更强.     

固体氩的晶格热导率的非简谐晶格动力学计算

用一种非简谐晶格动力学方法, 使用相互作用势作为惟一的输入参数, 准确地计算了固体氩的各个声子的频率和弛豫时间. 并将这些结果进一步和玻尔兹曼输运方程相结合, 预测了固体氩从10 K 到80 K 区间的热导率, 并得到了与实验值非常符合的结果. 分析了运用非简谐晶格动力学方法进行数值计算过程中的各个相关的计算参数, 包括布里渊区中倒格子矢量的选取, δ 函数的展宽的选择等对热导率和声子弛豫时间预测结果的影响. 通过对各个声子模式对热导率贡献的分析, 发现随着温度升高, 高频声子对于热导率的贡献率也逐渐变大, 结果和理论预测完全一致. 关键词： 热导率 固体氩 非简谐晶格动力学 声子     

辐照损伤对钨晶格热导率影响的分子动力学研究

钨是最具应用前景的面向等离子体候选材料,但核聚变堆内强烈的辐照环境会使钨的近表面区域产生辐照损伤,进而影响其关键的导热性能.本文构建了包含辐照损伤相关缺陷的晶体钨模型,并采用非平衡分子动力学的方法定量研究了这些缺陷对钨导热性能的影响.结果表明,随中子辐射能量的增加,晶体内部留下的Frenkel缺陷数目增多进而导致钨的晶格热导率降低;间隙原子比空位更易于向晶界偏聚,且钨中的间隙钨原子与空位相比,使晶格热导率下降程度更大.纳米级氦气泡导致晶格热导率的显著降低,气孔率为2.1%时晶格热导率降至完美晶体的约25%.这些不同的缺陷造成不同程度的周围晶格扭曲,增加了声子散射几率,是导致晶格热导率下降的根源.     

Ag-ZnO纳米复合热电材料的制备及其性能研究

ZnO是一类具有潜力的热电材料, 但其较大声子热导率影响了热电性能的进一步提高. 纳米复合是降低热导率的有效途径. 本文以醋酸盐为前驱体, 溶胶-凝胶法制备了Ag-ZnO纳米复合热电材料. 扫描电镜照片显示ZnO颗粒呈现多孔结构, Ag纳米颗粒分布于ZnO的晶粒之间. Ag-ZnO纳米复合材料的电导率比未复合ZnO材料高出100倍以上, 而热导率是未复合ZnO材料的1/2. 同时, 随着Ag添加量的增加, 赛贝克系数的绝对值逐渐减小. 综合以上原因, 添加7.5%mol Ag的Ag-ZnO纳米复合材料在700 K时的热电优值达到0.062, 是未复合ZnO材料的约25倍. 在ZnO基体中添加导电金属颗粒有利于产生导电逾渗通道, 提高材料体系的电导率, 但同时导致赛贝克系数的绝对值减小. 总热导率的差异来源于声子热导率的差异. 位于ZnO晶界的纳米Ag颗粒, 有利于降低声子热导率. 关键词： 热电材料 ZnO 纳米复合 热导率     

纳米线阵列横向输运的热电特性研究

利用包络函数的平面波展开法计算准二维纳米线阵列中的电子态,获得电输运系数表达式.同时,通过合理近似考虑边界散射对声子输运的影响,计算得到了晶格热导率.以Si/Ge体系为例,研究了纳米线阵列横向输运的热电特性.结果表明：结构优值与费米能级、纳米线直径及间距等参数相关.通过对结构参数的调整,纳米线阵列的横向输运可有效提高热电性能. 关键词： 热电性能 纳米线阵列 Seebeck系数 晶格热导率     

非晶锂离子导体在高压下的电特性

 本文首次测量了非晶态锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃（x=0.05及0.15）在0.000 1~0.80 GPa压力下的离子电导率及激活体积，发现激活体积在一定压力下由负变正，并用离子迁移通道的物理图象给出初步的微观解释。此外，还比较了整片非晶与粉末压片的异同，以及氧化铝组分不同对压力相变点的影响。观测到压力增强及卸压后电导率的弛豫现象——减至常压后离子电导比加压前提高10.4倍。     

Two-dimensional square-Au_2S monolayer: A promising thermoelectric material with ultralow lattice thermal conductivity and high power factor

The search for new two-dimensional(2 D) harvesting materials that directly convert(waste) heat into electricity has received increasing attention. In this work, thermoelectric(TE) properties of monolayer square-Au_2S are accurately predicted using a parameter-free ab initio Boltzmann transport formalism with fully considering the spin–orbit coupling(SOC),electron–phonon interactions(EPIs), and phonon–phonon scattering. It is found that the square-Au_2S monolayer is a promising room-temperature TE material with an n-type(p-type) figure of merit ZT = 2.2(1.5) and an unexpected high n-type ZT = 3.8 can be obtained at 600 K. The excellent TE performance of monolayer square-Au_2S can be attributed to the ultralow lattice thermal conductivity originating from the strong anharmonic phonon scattering and high power factor due to the highly dispersive band edges around the Fermi level. Additionally, our analyses demonstrate that the explicit treatments of EPIs and SOC are highly important in predicting the TE properties of monolayer square-Au_2S. The present findings will stimulate further the experimental fabrication of monolayer square-Au_2S-based TE materials and offer an in-depth insight into the effect of SOC and EPIs on TE transport properties.     

良导体热导率不同测量法的比较

维德曼-弗兰兹定律指出金属的热导率和电导率的比值是常数,本文先测量了一定温度下的材料的电阻率,再由电阻率计算出材料的热导率,并与利用热波法得到的热导率进行比较,其结果相近.     

Thermoelectric power of superionic conductor Ag7I4PO4

The thermoelectric power (θ) of Ag₇I₄PO₄ superionic conductor has been studied for the first time from 4 to 75°C; 80°C being its decomposition temperature. Relation between θ and temperature can be expressed by the equation

$\text{?θ = 0.20}\text{10}{}^3\text{T}\text{?0.255}$

for this solid. Analysis of the data yields 0.20 eV as heat of transport of Ag⁺ ion which is very close to its activation energy 0.21 eV. This supports the prediction of the theory of Rice and Roth based on “free-ion” model. This is also in consonance with earlier theories on heats of transport of ions in ionic solids. Indications have been found to justify the assumption that Ag₇I₄PO₄ has average structure.     

计算机辅助测量不良导体的导热系数

介绍了计算机数据采集及处理技术在不良导体导热系数测量实验中的应用及取得的结果．     

Study of lattice thermal conductivity of alpha-zirconium by molecular dynamics simulation

The non-equilibrium molecular dynamics method is adapted to calculate the phonon thermal conductivity of alphazirconium. By exchanging velocities of atoms in different regions, the stable heat flux and the temperature gradient are established to calculate the thermal conductivity. The phonon thermal conductivities under different conditions, such as different heat exchange frequencies, different temperatures, different crystallographic orientations, and crossing grain boundary (GB), are studied in detail with considering the finite size effect. It turns out that the phonon thermal conductivity decreases with the increase of temperature, and displays anisotropies along different crystallographic orientations. The phonon thermal conductivity in [0001] direction (close-packed plane) is largest, while the values in other two directions of [2īī0] and [01ī0] are relatively close. In the region near GB, there is a sharp temperature drop, and the phonon thermal conductivity is about one-tenth of that of the single crystal at 550 K, suggesting that the GB may act as a thermal barrier in the crystal.     

Effect of phonon scattering mechanisms on the lattice thermal conductivity of skutterudite-related compound

We have prepared the skutterudite-related compounds FeCo_3Sb_{12} and La_{0.75}Fe_3CoSb_{12} with different average grain sizes (about 0.8 and 3.9μm) by hot pressing. Samples were characterized by XRD, EPMA and SEM. The lattice thermal conductivity was investigated in the temperature range from room temperature to 200℃. Based on the Debye model, we analyse the change in lattice thermal conductivity due to various phonon scattering mechanisms by examining the relationship between the weighted phonon relaxation time τ(ω/ω_D)^2 and the reduced phonon frequency ω/ω_D. The effect of grain boundary scattering to phonon is negligible within the range of grain sizes considered in this study. The large reduction in lattice thermal conductivity of FeCo_3Sb_{12} compound contributes to the electron－phonon scattering. As for La_{0.75}Fe_3CoSb_{12} compound, the atoms of La filled into the large voids in the structure of the skutterudite produce more significant electron－phonon scattering as well as more substitute of Fe at Co site at the same time. Moreover, the point-defect scattering appears due to the difference between the atoms of La and the void. In addition, the scattering by the rattling of the rare-earth atoms in the void is another major contribution to the reduced lattice thermal conductivity. Introducing the coupling of the electron－phonon scattering with the point-defect scattering and the scattering by the rattling of the rare-earth atom is an effective method to reduce the lattice thermal conductivity of the skutterudite-related compounds by substitution of Fe for Co and the atoms of La filled in the large voids in the skutterudite structure.