Preparation and Microwave Sinterability of Mn<SUB>0.43</SUB>Ni<SUB>0.9</SUB>CuFe<SUB>0.67</SUB>O<SUB>4</SUB> NTC Thermistor Materials by Pechini Method

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 degrees C, 750 degrees C and 850 degrees C). The calcined Mn0.43Ni0.9CuFe0.67O4 powders were pressed and then sintered at 1000 degrees C 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 degrees C) and densified uniform microstructures. Microwave sintering can obtain the components with well uniformity of B constant and resistivity, of which the B-avg is 1930K (deviation of 0.31%) and resistivity rho(avg). is 135 Omega center dot cm (deviation of 4.55%). However, the B-avg is 1720K (deviation of 1.47%) and resistivity rho(avg). is 78 Omega center dot 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 255 Omega and 305 Omega for the microwave-sintered samples. The R-b and Rg, are respectively 200 Omega and 230 Omega for conventionally sintered samples.