LOW TEMPERATURE SYNTHESIS AND ELECTRONIC PROPERTIES OF NTC TEMPERATURE SENSOR SPINEL-TYPE OXIDES NANOPOWDERS

摘要

NiCo_xMn_(2-X)O_4 (x = 0.4; 0.8; 1.2; 1.6) thermistor with nanopowders have been synthesized by the auto-combustion method at low temperatures. The size and morphology of the calcinated powders have been investigated using XRD and TEM techniques. The average particle size was estimated to be about 65 nm in diameter with the cubic and cubic + tetragonal phases for low and high cobalt concentrations, respectively. The grain size of NTC ceramics sintered at 1200℃ is verified with scanning electron microscopy (SEM) images. Upon increasing the cobalt concentration, the grain size of NTC samples increases from about 2μm to a fewμm in size. The formation of spinel structure of powders has been studied by Fourier transform infrared (FTIR) spectroscopy. An ab initio calculation of electronic properties of NiCo_(0.8)Mn_(1.2)O_4 using full potential of the linear augmented plane wave (FP-LAPW) method has been performed. The results indicate that only the 3d-Mn orbitals play an important role in the conduction mechanism. The dependency of material resistivity constant (B) and temperature coefficient (α) have been measured.