Electrical Characterization of Polymethylsiloxane/MoSi 2 ‐Derived Composite Ceramics

High‐temperature‐resistant ceramics in the system Mo‐Si‐O‐C were prepared from polymethylsiloxanes loaded with MoSi 2 filler. Irreversible structural rearrangement reactions in the polymer‐derived Si‐O‐C matrix phase and at the filler‐matrix interface during heat treatment were detected by in situ electrical resistance measurements and impedance spectroscopy. At low temperatures a large difference in thermal expansion between the polymer and the filler resulted in an increase of resistance from 0.05 to 560 Ω·cm when the temperature was raised from 20° to 680°C. An increase of filler particle contact distances resulted in a high positive temperature coefficient (PTC 200°C = 4.64 K −1 ). At high temperatures carburization reaction of the filler on the particle surface resulted in contact formation which gave rise to a resistance lower than 10 −3 Ω·cm above 1000°C.