Synthesis and properties of Mn1.05−yCo1.95−x−z−wNixMgyAlzFewO4 NTC ceramic by co-precipitation method

Mn1.05−yCo1.95−x−z−wNixMgyAlzFewO4 negative temperature coefficient (NTC) material was synthesized by double precipitation reacting method. The synthesis condition was optimized. Fourier infrared (FI) spectrometer indicated that the precursor was consisted of oxalate and hydroxide. The powder was studied by X-ray diffraction (XRD) to obtain the optimum calcination temperature of 800 °C. The ceramics were mainly in the cubic spinel structure except for the minority of cubic cobalt oxide. Scanning electron microscope (SEM) image showed that the grain size decreased with the increase of Al2O3 content in the ceramic. While the room temperature resistivity ρ25 increased from 3027 Ω cm to 16,911 Ω cm with increasing Al2O3 content. The material constants B25/85 and activity energies were in the range of 3592-3977 K and 0.3112-0.3330 eV, respectively. Complex impedance analysis indicated that the grain boundary resistivity increased with increasing Al2O3 content, whereas, the grain resistance remains virtually unchanged.