One-step sintering of SiGe thermoelectric conversion unit and its electrodes

Dense p-type and n-type SiGe thermoelectric conversion units were fabricated with a double-layer electrode of W/TiB₂ or W/MoSi₂ by using glass encapsulation hot-isostatic-pressing process. The TiB₂ and MoSi₂ layers were used to prevent the chemical reaction between the tungsten and SiGe materials. Si₃N₄ ceramic particles were added into the electrode materials to reduce the mismatch of the thermal expansion between the electrode and the SiGe. Finite element analysis showed that the addition of 40 vol% Si₃N₄ into the TiB₂ layer and 55 vol% Si₃N₄ into the MoSi₂ layer reduced the thermal residual stress to a much lower value than the strength of individual layer. Sintered units had electrical resistivities of (1.5–2.0) × 10⁻³ Ω cm in the SiGe zone and 10⁻⁴ Ω cm in the electrodes. The comparison of the thermoelectric properties of the SiGe sintered with and without electrodes confirmed that the electrodes did not deteriorate the Seebeck coefficient of the SiGe alloys.