Electrical properties and aging behavior of Na-doped Mn1.95Co0.21Ni0.84O4 NTC ceramics

Abstract Negative temperature coefficient (NTC) thermistors based on Mn1.95-x Co0.21Ni0.84NaxO4 (x = 0, 0.03, 0.06, 0.09) were prepared by a co-precipitation method, in combination with a solid-state reaction. X-ray diffraction (XRD) showed that the ceramics were composed mainly of spinel NiMn2O4 with some Na0.7MnO2.05 for Na-doping with x = 0.06. The grain size and resistivity of the ceramic samples is seen to first decrease and then increase with Na ion content. Furthermore, the value of ρ298K, B298/323 constant, and Ea of the ceramic samples are 1602–3118 Ω cm, 3693–3820 K, and 0.3182–0.3292 eV, respectively. The relative resistivity shift is 0.05% for Na doped sample with x = 0.06 when compared to 0.3% for Na-free ceramics. It is demonstrated that Na-doping could be an efficient way to decrease the resistivity and improve electrical stability of Mn–Co–Ni– Na–O oxide based NTC ceramics.