Thermoelectric Properties of Iron-Silicide with various baoudaries

还有全球变暖和化石燃料枯竭危机等问题。解决这些问题需要现有能源的替代能源。一种未来能源是由热电转换产生的。ZT和P分别为：byZT=σα^2/κ=σα^2/(κ_<el>+κ_<ph>)，P=σα^2，其中T为温度，σ为电导率，α为塞贝克系数，κ_<el>和κ_<ph>为由电子和声子输运引起的导热系数。β-FeSi_2因其含量丰富、无毒、耐热、抗氧化性能好而备受关注。β-FeSi_2的极性可以通过选择第三元素的掺杂而在p型和n型之间转换。掺入银、碳化硅等材料可提高β-FeSi_2的优值和功率因数。更重要的是，与这些元素或化合物混合的β-FeSi_2的微观结构或制造工艺决定了其热电特性。本研究的目的是阐明Co掺杂Ag、Cu或Sb的β-FeSi_2的热电性能与微观结构或制备工艺的关系。为了提高热电性能，在相变、机械合金化、自旋铸造和扩散的基础上控制晶界和相界面。利用透射电子显微镜和能量色散x射线显微分析设备对其微观结构进行了研究。测量了塞贝克系数和电导率，并将其与微观结构联系起来。得出的结论如下。在晶界和β相的基体中观察到富Ag、Cu或sb相。塞贝克系数随元素含量的增加呈非线性减小。掺银带的塞贝克系数较大。塞贝克系数与银的混合时间无关。电导率随银含量的增加呈非线性降低。由粉末压制而成的圆盘电导率大。功率因数达到最大接近2-3在% Ag的光盘。由于不同的微观结构，圆盘的载流子迁移率、有效电子质量或散射系数不同于锭或带。用球磨使粉末变得又细又圆。烧结使α相数量减少，ε相数量增加，导致退火后β相数量减少，ε相数量增加。通过球磨、烧结和退火等工艺提高了材料的电导率和功率因数。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