Effect of grain growth on electrical properties of silicon carbide ceramics sintered with gadolinia and yttria

The effect of grain growth on electrical properties of SiC ceramics sintered with a new additive system (Gd2O3-Y2O3) was investigated. Hot-pressing of β-SiC with 3 vol% Gd2O3-Y2O3 in a nitrogen atmosphere resulted in highly conductive SiC ceramics (∼10−2-10−3 Ω cm), whereas hot-pressing of the same specimen in an argon atmosphere resulted in semi-insulating SiC ceramics (∼108 Ω cm). This difference was due to the nitrogen (N) doping in SiC ceramics in the former case. The N-doping in SiC ceramics was achieved by grain growth of SiC grains via a solution-reprecipitation mechanism. The electrical resistivity of N-doped SiC ceramics decreased with an increase in grain size of SiC ceramics if there is no β → α phase transformation of SiC. The lowest electrical resistivity obtained was 8.9 × 10−3 Ω cm after 6 h sintering at 2000 °C under an applied pressure of 40 MPa in nitrogen.