Synthesis of nanocrystalline manganite powders via a gel auto-combustion process for NTC thermistor applications

Nanocrystalline Ni0.66ZnxMn2.34−xO4 (x=0, 0.5 and 1.0) powders were synthesized via an auto-combustion process of nitrate–citrate gels. The investigation on thermal decomposition process by DTA-TGA and XRD techniques showed that the dried gels can burn in a self-propagating combustion process in air to transform into single-phase, nanocrystalline manganite particles with spinel crystal structure. The synthesized powders are highly sintering active, and the well-densified Ni–Zn manganite ceramics with fine-grained microstructures were obtained at about 1100 °C. The Zn substitution for Mn increases the electrical resistivity. The obtained ceramics have an activation energy B values higher than 4200 K, and can be considered as advanced semiconducting materials for NTC thermistor applications.