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Silicon carbide (SiC) bicrystals were prepared by diffusion bonding, and their grain boundary was observed using scanning transmission electron microscopy. The n-type electrical conductivity of a SiC single crystal was confirmed by scanning nonlinear dielectric microscopy (SNDM). Dopant profiling of the sample by SNDM showed that the interface acted as an electrical insulator with a ~2-μm-thick carrier depletion layer. The carrier depletion layer contained a higher number of oxygen impurities than the bulk crystals due to the incorporation of oxygen from the native oxide film during diffusion bonding. Density functional theory calculations of the density of states as a function of the bandgap also supported these findings. The existence of a carrier depletion layer was also confirmed in a p-type polycrystalline SiC ceramic. These results suggest that the electrical conductivity of SiC ceramics was mostly affected by carrier depletion near the grain boundary rather than the grain boundary itself.

An electrically conductive SiC-Ti2CN composite was fabricated from β-SiC and TiN powders with 2 vol% equimolar Y2O3-Sc2O3 additives by conventional hot-pressing. The composite (electrical resistivity of nearly 10-4 Ω·cm) was wire electro discharge machined into a specimen having a thickness of 500 μm. Entrance clearance, machining time, number of shorts, material removal rate (MRR), counts, and the effects of the capacitance and voltage of conductive SiC-Ti2CN composite during micro electrical discharge drilling were measured and compared to those of SUS304. As the unit discharge energy increased, entrance clearance, machining time, and number of shorts decreased. A decrement in the number of shorts was the main reason for decrements in entrance clearance and machining time. MRR was proportional to unit discharge energy. The study to determine the location of shorts during electro discharge drilling was also conducted. It was founded that the short circuit occurred mainly at the beginning (0–1000 cts) because of low electrical density, and right before the exit (3000–5000 cts) owing to the difficulty of removing debris. Both the capacitance and voltage tended to be inversely proportional to the number of shorts.

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.

In this study, we investigated the electrical and thermal properties of SiC ceramics with 2 vol% equimolar Y2O3–RE2O3 (RE = Sm, Gd, Lu) additives. The three SiC ceramics with 2 vol% equimolar Y2O3–RE2O3 additives showed electrical conductivities on the order of ~103 (Ω·m)−1, which is one order of magnitude higher than that of the SiC ceramics sintered with 2 vol% Y2O3 only. The increase in electrical conductivity is attributed to the growth of heavily nitrogen-doped SiC grains during sintering and the confinement of oxide additives in the junction area. The thermal conductivities of the SiC ceramics were in the 176–198 W·(m·K)−1 range at room temperature. The new additive systems, equimolar Y2O3–RE2O3, are beneficial for achieving both high electrical conductivity and high thermal conductivity in SiC ceramics.

SiC–TiC0.5N0.5 composites were fabricated from β-SiC and TiN powders with 2 vol% equimolar Y2O3–Sc2O3 additives by conventional hot pressing. Thermal and mechanical properties of the SiC–TiC0.5N0.5 composites were investigated as a function of initial TiN content. Relative densities of ≥98.9% were achieved for all samples. The addition of a small amount of TiN increased thermal conductivity, flexural strength, and fracture toughness of SiC ceramics. However, further addition of TiN in excess of 10 and 20 vol% deteriorated both thermal conductivity and flexural strength of the composites, respectively. In contrast, the fracture toughness of the composites increased continuously from 4.2 to 6.2 MPa∙m1/2 with increasing initial TiN content from 0 to 35 vol%, due to crack deflection by TiC0.5N0.5. The maximum values of thermal conductivity and flexural strength were 224 W/m K for a 2 vol% TiC0.5N0.5 and 599 MPa for a 10 vol% TiC0.5N0.5 composite.