Preparation and electrical properties of Mn1.05−yCo1.95−x−z−wNixMgyAlzFewO4 NTC ceramic derived from microemulsion method

Highlights: • The NTC thermister nano-powders Mn1.05−yCo1.95−x−z−wNixMgyAlzFewO4 were prepared by microemulsion method. • The metal ions were subsided after twice sediment reaction. • The specimens show good electrical properties by doping some nontransition metals. -- Abstract: The NTC thermistor nano-powders of Mn1.05−yCo1.95−x−z−wNixMgyAlzFewO4 were prepared by microemulsion method. Scanning electron microscope (SEM) image showed that the particles were well distributed. The mean particle-size was 72 nm. The structure of the precursor was investigated with Fourier infrared spectrometer (FI). The compositions of the powder and the as-sintered ceramic were evaluated by Energy Disperse Spectroscopy (EDS). X-ray diffraction (XRD) result indicated that the sintered samples were in the spinel structure. The room temperature resistivity ρ25, material constant B25/85 and activation energies of the NTC thermistor are in the range of 1173–19,059 Ω cm, 3169–3771 k, 0.2672–0.3136 eV. The room temperature resistivity and B25/85 constant were found to increase with Al2O3 content. The Mn0.9Co1.2Ni0.21Mg0.15Al0.09Fe0.45(A2) and Mn0.9Co1.2Ni0.27Mg0.15Al0.03Fe0.45(A3) specimens both showed a 200 °C resistance drift (ΔR/R) within 10% after aging at 910 °C for 600 h