Preparation and characterization of Ni_0.6Mn_2.4O ₄ NTC ceramics by solid-state coordination reaction

The impact of synthesis parameters, such as calcination temperature and reaction time, on the microstructure, phase compositions and electrical properties of Ni_0.6Mn_2.4O₄ negative temperature coefficient (NTC) ceramics, which were synthesized via solid-state coordination reaction method, was systematically explained. With enhancing calcination temperature and time, the relative densities were raised, while the porosities diminished. A compact single-phase cubic spinel ceramic could be obtained after annealing at 1,100 and 1,150 C, while a secondary phase Mn₃O ₄ was detected when the annealing temperature raised to 1,200 C. For the ceramics calcinated at 1,100 or 1,150 C for 3 h, their resistivities were 2,133 and 2,178 cm, the thermal constant B, which reflects the temperature sensitivity of the NTC ceramics, were 3,820 and 3,857 K. While the ceramic prepared at 1,200 C for 3 h, the resistivity and the B value reached 2,273cm and 3,810 K, respectively. This phenomenon was attributed to the increase of lattice parameters and the reduction of Mn⁴⁺-Mn³⁺ at high temperatures.