ELECTRICAL PROPERTIES OF BIOMORPHIC SiC CERAMICS AND SiC/Si COMPOSITES FABRICATED FROM MEDIUM DENSITY FIBREBOARD

The dependence of the electrical resistivity and the Hall coefficient on the temperature in the range 1.8-1300 K and on magnetic fields up to 28 kOe was investigated for biomorphic SiC/Si (MDF-SiC/Si) composite and biomorphic porous SiC (MDF-SiC) based on an artificial cellulosic precursor (MDF - medium density fibreboards). Electric transport in MDF-SiC was effected by n-type carriers with a high concentration of about 10 exp(20)/cm3 and a low mobility of about 0.4 cm2/V.s. The specific features in the conductivity of MDF-SiC were explained by quantum effects arising in disordered systems and requiring quantum corrections to conductivity. TEM confirmed the presence of disordered structural features (nanocrystalline regions) in MDF-SiC. The conductivity of MDF-SiC/Si composites originates primarily from the Si component in the temperature range 1.8-500 K and at about 500 to 600 K the contribution of the MDF-SiC matrix becomes dominant.