Low temperature synthesis and characterization of NTC powder and its ‘lead free’ thick film thermistors

A general and simple chemical approach has been proposed to prepare negative temperature coefficient (NTC) powder material using commercially available tetra hydrated acetates of Mn, Co, Ni and oxalic acid. The thermal decomposition of Mn-Co–Ni oxalate at 700 °C leads to formation of spinel phases with fine powder material. Lead free thick film thermistor pastes were formulated using the synthesized spinel powders. Planar thick film thermistor patterns of the formulated pastes were screen printed on alumina substrates. The microstructure and electrical properties of these thick film thermistors were determined. Depending on the powder preparation, the prepared thick film NTC thermistors showed room temperature resistance in the range of 12–29 MΩ. The values of thermistor constant, β25/300 ranged from 4014 to 4223 K.