Synthesis of nanocrystalline Ni₁Co_0.2Mn_1.8O₄ powders for NTC thermistor by a gel auto-combustion process

Nanocrystalline Ni₁Co_0.2Mn_1.8O₄ powders were synthesized via a gel auto-combustion process of nitrate-citrate gels. The investigation on the gels by XRD shows that a stable sol-gel can be formed by adding ethylene glycol (EG) and adjusting the pH values. The dried gels exhibit auto-catalytic combustion behavior. The reaction mechanism has been given by detailed studies based on DTA-DSC and XRD techniques. After being sintered at about 1150 °C, well-densified NTC ceramics with B values higher than 3600 k were obtained. It is demonstrated that the synthesized powder is high sinter active, and can be used for NTC thermistor application.