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 were studied depending on the pyrolysis conditions and subsequent annealing. The electrical properties were analysed to be extremely sensitive with respect to variations of the chemical composition, the solid state structure and the microstructure of the Si-C-N materials. Therefore, electrical investigations 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) temperature, (ii) atmosphere and (iii) annealing time applied during synthesis. The main mechanism, which is proposed for the transport of charge carriers in the amorphous, highly disordered silicon carbonitride is the tunnelling of large polarons. In contrast, the electrical conductivity of the crystallised SiC/Si3N4-counterpart is dominated by the transport of electrons in the conduction band of nitrogen doped SiC particles. (C) 2000 Elsevier Science Ltd. All rights reserved.