Thermoelectric Properties of Iron-Silicide with various baoudaries

存在全球变暖和化石燃料枯竭危机等问题。为了解决这些问题，迫切需要替代现有能源的能源。热电转换是一种潜在的能源。ZT和P由ZT=σα^2/κ=σα^2/(κ_&lt；el&gt；+κ_&lt；ph&gt；)，P=σα^2给出，其中T是温度，σ电导率，α塞贝克系数，κ_&lt；el&gt；和κ_&lt；ph&gt；是电子和声子输运的导热系数。β-FeSi_2因其丰富且无毒，具有很高的耐热和抗氧化性能而引起人们的关注。通过选择第三种元素的掺杂，β-FeSi2的极性可以在p型和n型之间转换。掺入银或碳化硅陶瓷等物质可以提高β-FeSi2的品质因数和功率因数。有趣的是，热电道具…β-FeSi_2的热电性能主要取决于掺入这些元素或化合物的β-FeSi_2的微观结构或制备工艺。本研究的目的是阐明掺Co的Ag、Cu或Sb等掺杂的FeSi_2的热电性能与微观结构或制备工艺的关系。为了提高材料的热电性能，在相变、机械合金化、旋铸和扩散的基础上对晶界和相界进行了控制。用透射电子显微镜和能量色散X射线微区分析仪研究了材料的微观结构。测量了样品的Seebeck系数和电导率，并与微观结构进行了关联。结果表明：在β相的晶界和基质中观察到富银、富铜或富Sb相，塞贝克系数随元素含量的增加呈非线性下降。掺银薄带的Seebeck系数较大。Seebeck系数与与Ag混合的时间无关。随着Ag含量的增加，电导率呈非线性下降。在粉末压制成型的圆盘中，导电率较大。晶片的功率因数在2-3at%Ag附近达到最大值。晶片的载流子迁移率、有效电子质量或散射因数因微观结构不同而不同于铸锭或带材。粉末经过球磨后变得细小而圆整。烧结减少了α相的数量，增加了ε相的数量，导致了热处理后β相的减少和ε相的增加。通过球磨、烧结和回火处理，提高了材料的导电性和功率因数。较少

There are problems such as the global warming and fossil fuel depletion crisis. Alternative energy to current energy is desired to solve these problems. One of prospective energies is generated from thermoelectric conversion. The conversion efficiency and generating power become higher with higher figure of merit ZT and higher power factor P. The ZT and P are given byZT=σα^2/κ=σα^2/(κ_<el>+κ_<ph>),P=σα^2,where T is temperature, σ electrical conductivity, α Seebeck coefficient, κ_<el> and κ_<ph> being thermal conductivity due to electron and phonon transportations.The β-FeSi_2 attracts attention for the thermoelectric conversion, because it is abundant and free of toxicity, being high heat-resistant and oxidation-resistant. The polarity of β-FeSi_2 is convertible between p- and n-type with selecting the dopant of third element. The figure of merit and power factor of β-FeSi_2 are enhanced by mixing substances such as Ag, or SiC ceramics etc. It is interesting how the thermoelectric prop … More erties depend on microstructures, or fabrication processes of β-FeSi_2 which is mixed with such elements or compounds.The objective of the present research is to clarify the relation between the thermoelectric properties and microstructures or fabrication processes in the Co doped β-FeSi_2 which is mixed with Ag,Cu or Sb ete. In order to enhance the thermoelectric performance, crystal grain boundaries and phase interfaces were controlled on the basis of phase transformation, mechanical alloying, spin-casting and diffusion. The microstructures were investigated by using a transmission electron microscope with an energy dispersion X-ray microanalysis equipment. The Seebeck coefficient, and electrical conductivity were measured and related to the microstructures. The drawn conclusions are given as follows.The Ag,Cu,or Sb-rich phase is observed at the grain boundaries and in the matrix of the β phase.The Seebeck coefficient decreases nonlinearly with increasing the element content. The Seebeck coefficient is large in the ribbon mixed with Ag. The Seebeck coefficient is independent of timing of mixing with Ag. The electrical conductivity decreases nonlinearly with increasing Ag content. The electrical conductivity is large in the discs which are formed by pressing powder. The power factor reaches to maximum near 2-3 at% Ag for the discs.Carrier mobility, effective electron mass, or scattering factor of the discs differs from that of ingot, or ribbon, because of different microstructures.The powder becomes fine and round with ball milling. Sintering reduces the amount of the α phase and increases the amount of ε phase, resulting in decreasing of the β phase and increasing in the ε phase after annealing. The electrical conductivity and the power factor are enhanced by ball-milling, sintering and annaling. Less