Study on the preparation and electrical properties of NTC thick film thermistor deposited by supersonic atmospheric plasma spraying

In the present work, a series of thick Ni_0.6Mg_0.3Mn_1.5−xAl_0.6+xO₄(x = 0, 0.1, 0.2, 0.4, 0.6) films (50 ± 10 μm) with negative temperature coefficient (NTC) were firstly deposited by newly developed high efficiency supersonic atmospheric plasma spray (SAPS) method. The phase, microstructure and electrical properties of films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and two-probe technique. The results showed that all the films were composed of cubic spinel structure, and the MgAl₂O₄ phase increased with increasing the Al₂O₃ content in the original powders. In addition, the films showed a dense and smooth surface with some pores in the grain boundaries. All the as-sprayed films showed a linear relationship between ln resistivity and reciprocal of absolute temperature (1/T) in the temperature range from 25 °C to 220 °C, which indicated a NTC characteristic.