Anisotropy of electric resistivity of Sapele-based biomorphic SiC/Si composites

The electrical resistivity of Sapele-based biomorphic SiC/Si materials was measured in a wide temperature range from 10 K to room temperature. The samples were fabricated by the reactive infiltration of molten silicon into a carbonized Sapele (African Entandrophragma Cylindricum) wood preform. All the samples studied contained residual Si (10–35 wt %). It was found that the resistivity-temperature (ρ(T)) dependences have semimetallic behavior which becomes very close to linear metallic behavior at 100 < T < 300 K. The obtained values of resistivity were quite low (ρ ≈ 0.002–0.02 Ω cm) and showed strong anisotropy: the resistivity along the wood growth axis was several times lower than that in the perpendicular direction. The extent of this anisotropy was in correlation with the amount of residual Si (and, hence, with the amount of residual porosity) in a sample. The resistivity perpendicular to the wood growth axis drastically increased with the Si content, whereas the resistivity parallel to it was practically independent of the Si content. It is suggested that the presence of residual carbon in the samples and carrier scattering at SiC/Si interphases could determine the observed character of ρ(T) dependences.