Electrical properties and aging mechanism of Y_2O_3-MCr_(0.5)Mn_(0.5)O_3 (M = Sm, Gd) composite NTC ceramics

摘要

We report the structure and negative temperature coefficient (NTC) electrical properties of Y_2O_3-MCr_(0.5)Mn_(0.5)O_3 (M = Sm, Gd) composite thermistor ceramics. The high-temperature aging mechanism has been revealed by using defect chemistry theory in combination with X-ray photoelectron spectroscopy analysis. The composite ceramics consist of Y_2O_3 and perovskite phase. All the NTC thermistors show a linear relationship between the natural logarithm of the resistivity and the reciprocal of the absolute temperature, indicative of the small-polaron hopping conductivity. The resistivity increases with the increase of Y_2O_3 content for Y_2O_3-SmCr_(0.5)Mn_(0.5)O_3 and Y_2O_3-GdCr_(0.5)Mn_(0.5)O_3 composite ceramics, respectively. The resistivity at 300 ℃ is in the range 10~2-10~4 Ω cm together with a B_(300/800) from 4163 to 5614 K. The resistance decreases after high-temperature aging, suggesting that both aging atmosphere and the concentration of oxygen vacancies play a significant role in the change of electrical conductivity.