Preparation and Properties of Thermoelectric Materials by PM Process.

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In this study, the preparation process and the thermoelectric properties of beta-FeSi_2 and gamma-LaS_x were investigated. The results are summarized as follows:1. Preparation and properties of beta-FeSi_2.1.1. Effect of Mechanical Grinding(MG)MG and Hot-pressing significantly improved the densification and transition from alpha+epsilon phase to beta-phase. Finely dispersed epsilon-phase in beta-FeSi_2 by MG increased the thermoelectric properties by decreasing the resistivity.1.2. Effect of Co, Ni, B Addition.Co, Ni addition markedly accelerated the sintering of FeSi_2, while B addition hindered the sintering. Co addition increased the thermoelectric power, while Ni and B addition decreased the thermoelectric power.2. Preparation and properties of gamma-LaS_x.Thre are three phases(alpha、beta、gamma) in LaS_x(4/3*X*3/2) and gamma-LaS_x phase is expected to be good thermoelectric material. However, the conditions to prepare gamma-LaS_x phase have not been clarified. In this study, the preparation process of gamma-LaS_x and their thermoelectric properties were investigated. Through solid phase reaction between metallic La and S ina quartz capsule at 1273 K, it became clear that gamma-phase was obtained in the low S compositions.