Sintering and electrical properties of Mn–Co–Fe–Zn–Ni–O high-entropy ceramics for NTC thermistors

In this work, the dual-phase structure Mn–Co–Fe–Zn–Ni–O high-entropy negative temperature coefficient (NTC) ceramics were synthesized by a solid-phase reaction method. The ceramics are mainly composed of the cubic spinel phase and the rock salt phase. Electron microscopic images revealed the typical morphology and the homogeneous distribution of all elements. The results confirmed that the microstructure and electrical properties of the high-entropy ceramics are closely related to the sintering temperature. As the sintering temperature increased, the content of the rock salt phase gradually improved, meanwhile, the higher resistivity of samples was achieved. Notably, it was found that an appropriate proportion of the rock salt phase could significantly enhance the aging stability of ceramics. The aging drift of the samples sintered at 1175 °C was only 0.632 %. In addition, the ratio of the two phases was adjusted by adding NiO. The ρ25 and B25/50 of the materials can be tuned in the range of 22.25 kΩ cm∼24.19 kΩ cm and 4047 K–4145 K, respectively. Regulating the phase ratio of dual-phase materials is a novel strategy for designing NTC ceramic materials with excellent characteristics. This work provides an idea for future research on high-entropy NTC thermistor ceramics.