The Mn0.9Co1.2Ni0.27Mg0.5Al0.03Fe0.45O4negative temperature coefficient (NTC) ceramics derived from nano-particles were sintered at 1380 °C, 1450 °C and 1560 °C, respectively. X-ray diffraction (XRD) result showed that the ceramics sintered at 1380 °C and 1450 °C were mainly in the cubic spinel structure except for a little of tetragonal spinel, and that sintered at 1560 °C was consisted of cubic spinel and cubic cobalt oxide phase. Scanning electron microscopy (SEM) image indicated that the grain size of the ceramic increased sharply when the sintering temperature increased from 1380 °C to 1450 °C, and it changed little when the temperature further increased to 1560 °C, while the porosity was enlarged seriously. Thus a perfect sintering temperature of 1450 °C was proposed. Impedance analysis revealed that the grain resistance Rgshowed positive temperature coefficient thermistor characteristic, while the grain boundary resistance Rgbpossessed negative temperature coefficient characteristic. Because the grain boundary resistance Rgbwas two orders of magnitude larger than the grain resistance Rg, the material thus showed negative temperature coefficient thermistor characteristic.
Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, Key Lab Funct Mat & Devices Special Environm, Xinjiang Key Lab Elect Informat Mat & Devices, Urumqi 830011, Peoples R China;Univ Chinese Acad Sci, Beijing 100049, Peoples R China
Xia, Junbo,Zhao, Qing,Gao, Bo,et al. Sintering temperature and impedance analysis of Mn0.9Co1.2Ni0.27Mg0.15Al0.03Fe0.45O4 NTC ceramic prepared by W/O microemulsion method[J]. Journal of Alloys and Compounds,2014,617(12):228-234.