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In this study, the effect of nitrogen (N) doping and microstructural changes on the electrical and thermal properties of silicon carbide (SiC) were investigated. SiC powder was treated in a N 2 atmosphere at 1673, 1973 and 2273 K for 3 h and subsequently sintered by spark plasma sintering (SPS) at 2373 K for 300 s in a vacuum or in a N 2 atmosphere. The a-axis of the N 2 -treated SiC powders was almost constant, while the c-axis slightly decreased with an increase in the temperature of N 2 treatment. The relative density of the SiC powder sintered body decreased from 72% to 60% with an increase in the temperature of N 2 treatment. The increase in temperature of N 2 treatment caused a decrease in the thermal and electrical conductivities of the SiC. Upon N 2 treatment at 1673 K and sintering in a N 2 atmosphere, SiC exhibited a high electrical conductivity of 1.5 × 10 3 S m −1 at 1123 K. SiC exhibited n-type conduction, and the highest Seebeck coefficient was −310 μV K −1 at 1073 K.

Off-stoichiometric silicon carbide (SiC), C-and Si-added SiC (6H, α-type), with an excess amount of C or Si from 1 to 5 mol%, were fabricated by spark plasma sintering at 2373 K and 50 MPa in a vacuum. The microstructure, electrical, and thermal properties of offstoichiometric SiC were investigated. The lattice parameters increased after the addition of C and Si, suggesting the formation of solid solutions of C and Si in SiC. The addition of C and Si increased the densification, while the addition of a small amount of Si (1 mol%) significantly improved the densification. The electrical conductivity (σ) of C-added SiC was 0.7-1.4 × 10 2 S m −1 at 298-1150 K. The Seebeck coefficient of C-added SiC changed from nto p-type with increasing addition of C, whereas that of Si-added SiC was almost independent of the amount of Si added. The thermal conductivity of C-and Si-added SiC was in the range of 180-250 W m −1 K −1 , which was greater than that of pristine SiC (100 W m −1 K −1 ) at room temperature.

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