Electrical properties of amorphous SiCxNyHz-ceramics derived from polyvinylsilazane

Electrical properties of monolithic, amorphous SiCxNyHz-ceramics derived from 1,3,5-trimethyl-1,3,5-trivinyicyclotrisilazane via polymer pyrolysis were investigated from room temperature to 400 degreesC using impedance spectroscopy. Depending on the pyrolysis temperature T-p the d.c. conductivity varies up to 8 orders of magnitude. The temperature dependence of samples pyrolysed at low temperatures (T-p = 700-1200 degreesC) follows a Mott law, whereas samples pyrolysed at high temperature (T-p = 1400 degreesC) show an Arrhenius dependence. Structural changes during pyrolysis were characterized by solid state magic angle spinning nuclear magnetic resonance spectroscopy, Raman spectroscopy and X-ray diffractometry. NMR and especially Raman measurements indicate the formation of sp(2)-carbon atoms, which rearrange towards graphitic-like domains with increasing pyrolysis temperature. This observation can explain the related increase of the d.c.-conductivity. (C) 2002 Elsevier Science Ltd. All rights reserved.