Effect of Sintering Temperature and Nb, Mn Doping Amount on Temperature Resistance Characteristics of Lead Barium Titanate Based High Curie Point PTC Ceramics

The Nb-Mn Co-doped lead barium titanate based high Curie point positive temperature coefficient (PTC) ceramics were prepared by solid state reaction after adding lead, strontium, calcium, niobium and manganese into barium titanate ceramics. The effects of the composite doping of Nb and Mn (molar fraction of 0.002 0–0.003 0, 0.000 8–0.002 5, respectively) on the microstructure, bulk density and temperature resistance characteristics of the ceramics under different sintering temperatures (125 0–131 0 ℃) were studied. The results show that the bulk densities of ceramics doped with different molar fractions of Mn or Nb first increased and then decreased with the increase of sintering temperature. When the sintering temperature was 1 290 ℃, the bulk densities were the largest, and their structures were all pure chalcocite structures. When the sintering temperature was 1 290 ℃, with the increase of Mn doping amount, the bulk density of the ceramics first increased and then decreased, the grain size increased, the room temperature resistivity increased, the lift-off resistance ratio and the temperature coefficient basically first increased and then decreased, and the Curie temperature was stabilized at 271–280 ℃. With the increase of Nb doping amount, the bulk density of the ceramics first increased and then decreased, the grain size decreased, the lift-off resistance ratio and temperature coefficient first increased and then decreased, the room temperature resistivity first decreased and then increased, and the Curie temperature was stabilized at 270–281 ℃. When the sintering temperature was 1 290 ℃, the molar fractions of doped Mn and Nb were 0.001 0, 0.002 4, respectively, the temperature resistance characteristics of the ceramics were the best; the lift-off resistance ratio and temperature coefficient were the largest, which were 7.011×10³ and 20.19%, respectively, the room-temperature resistivity was 2.13×10³ Ω·cm, and the Curie temperature was 281 ℃. The excellent temperature resistance was ascribed to the uniform the grain size and the largest bulk density.