Abstract: In order to obtain the NTC thermistors with small B constant (about 1900K), applied to wide temperature range, Mn0.43Ni0.9CuFe0.67O4 NTC thermistor materials prepared by Pechini method were microwave-calcined at different temperatures (650℃, 750℃ and 850℃). The calcined Mn_0.43Ni_0.9CuFe_0.67O₄ powders were pressed and then sintered at 1000℃ in a microwave furnace (multimode cavity, 2.45GHz).The crystal structure, phase compositions, morphology and particle size distribution of the samples were analyzed by FT-IR, X-ray diffraction (XRD), scanning electron microscope (SEM) and a laser particle size analyzer. The experimental results show that the electrical properties of the ceramics are strongly dependent on the calcination and sintering process. The application of microwave leads to a lower calcination temperature (650℃) and densified uniform microstructures. Microwave sintering can obtain the components with well uniformity of B constant and resistivity, of which the Bavg. is 1930K (deviation of 0.31%) and resistivity ρ_avg. is 135Ω·cm (deviation of 4.55%). However, the B_avg. is 1720K (deviation of 1.47%) and resistivity ρavg. is 78Ω·cm (deviation of 25.34%) for the conventionally sintered components. From complex impedance analysis, the grain resistance (R_b) and grain boundary resistance (R_gb) are respectively 255Ω and 305Ω for the microwavesintered samples. The R_b and R_gb are respectively 200Ω and 230Ω for conventionally sintered samples.

Key words: microwave sintering, microwave calcining, NTC, pechini method