Electrical Properties of CuO-doped SrFe_(0.9)Sn_(0.1)O_(3-δ) Thick Film NTC Thermistors

CuO-doped SrFe0.9Sn0.1O3-δ(CSFS) thick-film negative temperature coefficient(NTC) thermistors(20mol%,30mol%,40mol%,50mol%) were prepared by the screen printing method.The microstructures and electrical properties of CSFS thick films were determined.With the increase of CuO content,the surface morphology of thick films becomes denser.The room-temperature resistance values gradually decreases to about 0.46 MΩ and the thermistor-constant values are basically constant at around 3300 K.After the addition of CuO,SrFe0.9Sn0.1O3-δ is decomposed into various SrFe1-xSnxO3-δ(0.1x1) phases.By two-RQ series equivalent circuit model,impedance characteristics of the thick film containing 40mol% CuO content are investigated over the measured temperature range of 25–250℃.It is found that the total thick-film resistance is mainly attributed to the contribution of grain and grain boundary resistances,both of which show the typical NTC thermistor characteristics.Furthermore,the complete match of peak frequencies between the imaginary parts of impedance and electric modulus suggests that delocalized conduction is the main conduction mechanism in the thick-film NTC thermistors.