MnFe2O4-based NTC thermosensitive ceramics modified by Bi2O3/TiO2 additives

Negative temperature coefficient (NTC) thermistors are the key components in the fields of temperature sensors and electronic information. In order to significantly reduce the sintering temperature of ceramics and simultaneously obtain a large NTC material constants ( B values), herein the Bi ₂ O ₃ /TiO ₂ modified MnFe ₂ O ₄ ceramics were fabricated for the high sensitive NTC thermistors. Various contents of Bi ₂ O ₃ or Bi ₂ O ₃ +TiO ₂ were added into the pre-calcined MnFe ₂ O ₄ powders, followed by being granulated, shape forming, and sintering. The Bi ₂ O ₃ /TiO ₂ modified MnFe ₂ O ₄ ceramics can be obtained by sintering at 1060°C, while the sintering temperature of pure MnFe ₂ O ₄ ceramics was 1250°C. All the prepared ceramics show typical NTC characteristics. Both Bi ₂ O ₃ and Bi ₂ O ₃ /TiO ₂ additives reduce the room temperature resistivity of the MnFe ₂ O ₄ based ceramics that still maintain high NTC material constants with the B values higher than 4460 K. The effect of Bi ₂ O ₃ /TiO ₂ contents on the phase component, elemental valence states, microstructures, electrical properties and aging behavior of the MnFe ₂ O ₄ based ceramics were investigated. The optimized Bi ₂ O ₃ /TiO ₂ modified MnFe ₂ O ₄ ceramics exhibit high electrical stability with a resistance drift rate of 1.27% after 500 h aging at 125°C in air. The aging characteristics were investigated by analyzing the evolution of the cation valence states before and after aging treatment.