Electrical resistivity of silicon nitride-silicon carbide based ternary composites

摘要

New electrically conductive ternary composites were developed by adding 8 vol.% of ZrN or ZrB_2 to a Si_3N_4-SiC matrix. During hot pressing, ZrB_2 reacted with S13N4 to form ZrSi_2, ZrN, Si and BN whereas added ZrN did not undergo any reactions in the Si_3N_4-SiC-ZrN composite. The composites modified by ZrN or ZrB_2 addition showed a lower resistivity (7 × 10~3 Ω cm and 3 × 10~(-1) Ω cm) compared to the matrix (3 × 10~4 Ω cm). Further studies on the grain size distribution and the volume ratio of conducting and non-conducting phases excluded a percolation network of ZrN and ZrSi_2 grains. In fact, doping of SiC grains and modified grain boundaries as a consequence of the formation of liquid phases during sintering are suggested to be the reason for the significantly lower resistivity of materials containing ZrSi2.A decrease in the composite resistivity due to a subsequent heat treatment was obtained for all hot-pressed composites.