Effects of Mechanical Alloying and Copper Addition on Thermoelectric Properties of n-Type and p-Type β-FeSi<SUB>2</SUB>

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  • Nagai Hiroshi
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University
  • Katsuyama Shigeru
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University
  • Nakayama Shogo
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University
  • Kobayashi Hideaki
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University
  • Majima Kazuhiko
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University
  • Ito Mikio
    Department of Materials Science and Processing, Faculty of Engineering, Osaka University

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  • Effects of Mechanical Alloying and Copper Addition on Thermoelectric Properties of n-Type and p-Type β-FeSi2
  • Effects of Mechanical Alloying and Copp
  • Effects of Mechanical Alloying and Copper Addition on Thermoelectric Properties of n-Type and p-Type &beta;-FeSi<SUB>2</SUB>

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Abstract

The effects of mechanical alloying (MA) process by vibration ball milling and Cu addition on the thermoelectric properties of n-type Fe1−XCoXSi2 and p-type Fe1−XMnXSi2 have been investigated.<BR>It has been found by X-ray diffraction analysis that mechanical alloying (MA) even after a short period is very effective to form the β-phase from the mixture of the α-Fe2Si5 and ε-FeSi phases during hot-pressing. Both of the hot-pressed n-type and p-type samples are composed of mostly the β-phase with dispersion of a small amount of ε-phase particles. The amount of the ε-phase increases with increasing Cu addition. EDX analysis of the n-type and p-type samples has shown that the β-phase contains no Cu, while the ε-phase contains Cu and Co or Mn. Since the Co and Mn contents in the ε-phase are higher than in the β-phase, the increment of the amount of the ε-phase decreases the Co and Mn contents in the β-phase, and significantly changes the thermoelectric power. Cu addition to the n-type Fe1−XCoXSi2 significantly decreases the electrical resistivity, and a small amount of Cu addition increases the thermoelectric power, resulting in the improvement of the performance. It is considered that the decrease in the electrical resistivity results from the dispersion of the metallic ε-phase in the semiconducting β-phase matrix. On the other hand, Cu addition to the p-type Fe1−XMnXSi2 decreases the performance, which results from a significant decrease in the thermoelectric power due to the decrease in the Mn content of the β-phase as well as the dispersion of the metallic ε-phase. The thermal conductivity of the n-type and p-type samples is slightly increased by Cu addition.

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