Silicon carbonitride ceramics derived from polysilazanes Part II. Investigation of electrical properties

Electrical properties such as d.c.- and a.c.-conductivity, permittivity as well as thermopower of polysilazane-derived silicon carbonitride ceramics w ere studied depending on the pyrolysis conditions and subsequent annealing. The electrical properties were analysed to be extremely sensitive with res pect to variations of the chemical composition, the solid state structure a nd the microstructure of the Si-C-N materials. Therefore, electrical invest igations can be an important tool for the non-destructive characterisation of novel multicomponent carbide-nitride-based ceramics. In particular the d .c.-conductivity can be controlled within 15 orders of magnitude by (i) tem perature, (ii) atmosphere and (iii) annealing time applied during synthesis . The main mechanism, which is proposed for the transport of charge carrier s in the amorphous, highly disordered silicon carbonitride is the tunnellin g of large polarons. In contrast, the electrical conductivity of the crysta llised SiC/Si3N4-counterpart is dominated by the transport of electrons in the conduction band of nitrogen doped SiC particles. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.