Solution Synthesis of Cubic Spinel Mn–Ni–Cu–O Thermistor Powder

Toward the development of NTCR thermistors, nanocrystalline Mn–Ni–Cu–O powder was synthesized from a mixed chloride aqueous solution by a simple co-precipitation method.The introduction of an oxidizing agent (H(2)O(2)) into the solution led to the partial oxidation of Mn(2+) ions into Mn(3+) ions, which enabled the collected powder to be well crystallized at 650 °C. Such a low calcining temperature resulted in fine particles with a mean size of 60 nm, which significantly promoted densification of the resulting ceramics. As a result, a dense and homogenous microstructure with a relative density up to 97.2% was achieved for pellets sintered at 1100 °C. Furthermore, these sintered ceramics exhibited a room temperature resistivity (ρ(25)) of 67 Ω·cmand a thermistor constant (B(25/85)) of 2843 K, which make them suitable for use in industrial thermistors. In addition, electrical stability was greatly improved when the ceramics were prepared by a new two-step sintering method. The results suggest that the co-precipitation route with the introduction of H(2)O(2) is suitable for the fabrication of cubic spinel thermistor nanopowders.