Study of microstructure, impedance and dc electrical properties of RuO2–spinel based screen printed ‘green’ NTC thermistor

The NTC powder materials were prepared chemically using acetates of (Mn–Co–Ni), as precursor materials. The sintering of the powders shows the existence of spinel phases at comparatively low temperature, i.e. 800 °C. ‘Green’ thick films were prepared by admixing of the spinel powder, RuO2, lead free glass frit and the organic vehicle. Synthesized powders as well as the thermistor films were characterised by FTIR spectroscopy, TG/DTA, XRD and SEM. The electrical parameters like sheet resistance, thermistor constant, temperature co-efficient of resistance of the thick film thermistors are presented. The impedance of the thermistor films was measured and it has been correlated with the theoretical model and its equivalent circuit using the ‘Cole–Cole’ plots.