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 Ni0.6Mg0.3Mn1.5−xAl0.6+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.