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A dense silicon carbide (SiC) ceramic with a very high flexural strength at 2000 °C (981 ± 128 MPa) was obtained by conventional hot-pressing with extremely low additive content (2000 ppm Y2O3). Observations using high-resolution transmission electron microscopy (HRTEM) showed that (1) homophase (SiC/SiC) boundaries were clean without an intergranular glassy phase and (2) junction pockets consisted of nanocrystalline Y-containing phase embedded in an amorphous Y-Si-O-C-N phase. The excellent strength at 2000 °C was attributed to the clean SiC/SiC boundary and the strengthening effect of plastic deformation.

SiC-Zr 2 CN composites were fabricated from β-SiC and ZrN powders with 2 vol% equimolar Y 2 O 3 -Sc 2 O 3 additives via conventional hot pressing at 2000 °C for 3 h in a nitrogen atmosphere. The electrical and thermal properties of the SiC-Zr 2 CN composites were investigated as a function of initial ZrN content. Relative densities above 98% were obtained for all samples. The electrical conductivity of Zr 2 CN composites increased continuously from 3.8 × 10 3 (Ωm) −1 to 2.3 × 10 5 (Ωm) −1 with increasing ZrN content from 0 to 35 vol%. In contrast, the thermal conductivity of the composites decreased from 200 W/mK to 81 W/mK with increasing ZrN content from 0 to 35 vol%. Typical electrical and thermal conductivity values of the SiC-Zr 2 CN composites fabricated from a SiC-10 vol% ZrN mixture were 2.6 × 10 4 (Ωm) −1 and 168 W/m K, respectively.

Bulk SiC ceramics were fabricated by spark plasma sintering, and the effects of Y 2 O 3 addition on the structural and electrical properties were investigated. Raman spectroscopy revealed that SiC specimens with low Y 2 O 3 content (0.01 and 0.05 wt%) contained a graphitic phase (1580 and 2710 cm −1 ) which was insignificant for high Y 2 O 3 content (1.0 and 5.0 wt%). Carbon-rich SiC specimens exhibited p-type conduction character, while others exhibited n-type character. The p- and n-type SiC specimens had electrical resistivities around 10 −2 Ω cm but exhibited photoluminescence spectra quite different from each other. The p-type character is primarily attributable to silicon vacancies (V Si ), while the n-type character is ascribed to nitrogen substitution in carbon sites (N C ) of the zincblende lattice. The change in conduction type with yttria addition in the SiC specimen can be understood in terms of a competition between the densities of V Si and N C .

Dense SiC–Ti2CN composites were fabricated from β-SiC and 4 vol% TiN powders with 2 vol% equimolar Y2O3–RE2O3 (RE = Sm, Gd, Lu) additives by conventional hot pressing. Electrical and mechanical properties of the SiC–Ti2CN composites were investigated with a variation of sintering additive composition. Relative densities of ∼99.9% were achieved for all specimens. All specimens exhibited electrical resistivities on the order of ∼10−5 Ω m. These low electrical resistivities were attributed to heavy nitrogen doping in the SiC lattice (carrier density ∼1020 cm−3). Typical electrical resistivity, flexural strength, fracture toughness, and Vickers hardness values of the SiC–Ti2CN composite sintered with 2 vol% Y2O3–Lu2O3 additives were 2.2 × 10−5 Ω m, 722 MPa, 4.6 MPa m1/2, and 25 GPa, respectively.