Preparation of N-type Silicon Carbide-Based Thermoelectric Materials by Spark Plasma Sintering * 1

The SiC/Si 3 N 4 sintered materials were prepared by Spark Plasma Sintering at 2000 • C. The crystal structure of sintered materials is cubic β-SiC type with relative density higher than 80%. All sintered materials show n-type conduction and the carrier concentration increases with increasing Si 3 N 4 concentration. Seebeck coefficient α and electrical conductivity σ increased with increasing temperature indicating suitable for high temperature thermoelectric conversion. Thermoelectric properties are improved by addition of Si 3 N 4 and the power factor α 2 σ takes a maximum value at SiC-7 mass%Si 3 N 4

Thermoelectric properties of porous SiC/C composites

We developed a porous SiC/C composite by oxidizing a SiC/C composite made from a mixed powder of wood charcoal and SiO2 (32-45 mu m) by pulse current sintering at 1600 and 1800 degrees C under a N-2 atmosphere. The microstructures of the porous SiC/C composites with oxidation and the SiC/C composites without oxidation were analyzed by Raman spectroscopy and scanning electron microscopy (SEM). Raman spectra revealed the disappearance of excess carbon and the presence of beta-SiC. The porous microstructure was monitored by SEM observation as a function of the heat treatment temperature. The thermoelectric properties of porous SiC/C composites with oxidation and SiC/C composites without oxidation were investigated by measuring the Seebeck coefficient, the electrical conductivity and thermal conductivity. The Seebeck coefficient of all samples revealed n-type conduction, and the absolute value of the Seebeck coefficient for the porous SiC/C samples with oxidation was much larger than that for the SiC/C samples without oxidation. For the electrical conductivity the reverse is true. Only the thermal conductivity of the SiC/C sample heated to 1800 degrees C without oxidation was high initially and stayed rather high. In general, the thermoelectric properties improved at higher measurement temperatures indicating their suitability for high-temperature thermoelectric conversion. A maximum figure of merit of 2.01 x 10(-5) K-1 was obtained at 700 degrees C in porous SiC/C samples sintered at 1800 degrees C with oxidation. (c) 2007 Elsevier Ltd. All rights reserved