Electrical properties of Sr–Bi–Mn–Fe–O thick-film NTC thermistors prepared by screen printing

The Sr–Bi–Mn–Fe–O (Sr:Bi:Mn:Fe = 0.2:x:0.5:0.3; x = 0.6, 0.8, 1.0, 1.2) thick films with good NTCR characteristics were produced by screen-printing, using a paste with organic binders alone. X-ray diffraction patterns of the thick films showed two main phases of Sr0.3Bi0.7MnO3−y and SrFeO3−m with perovskite structure besides some amount of the bismuth iron oxides. It was found by SEM that the films with the different Bi content have superior morphology and to be dense. The room-temperature resistivity (ρ25), thermistor constant (B25/85), and activation energy (Ea) of the Sr–Bi–Mn–Fe–O NTC thermistor films increased with the increase of Bi content. The values of ρ25, B25/85, and Ea of the NTC thermistors were in the range of 406–1960 Ω cm, 3141–3693 K, and 0.275–0.324 eV, respectively. For composition x = 0.8, a maximum reliability of +3% resistivity drift and duration time over 800 h at aging temperature 300 °C were observed at sintering temperature 785 °C.