Preparation and Microwave Sinterability of Mn_(0.43)Ni_(0.9)CuFe_(0.67)O_4 NTC Thermistor Materials by Pechini Method

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 Mn0.43Ni0.9CuFe0.67O4 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 ρavg.is 135Ω·cm(deviation of 4.55%).However,the Bavg.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(Rb) and grain boundary resistance(Rgb) are respectively 255Ω and 305Ω for the microwave-sintered samples.The Rb and Rgb are respectively 200Ω and 230Ω for conventionally sintered samples.