Bulk ceramics and thick film thermistors prepared from modified nickel manganite (Ni0.5Cu0.2Zn1.0Mn1.3O₄) powder

NTC thermistors in form of bulk ceramics and thick film, with the nominal composition {Ni0.5Cu0.2Zn1.0Mn1.3O_4} , were prepared from fine manganite powder. The finemanganite powder with an average particle size of ~0.5 μm was obtained by calcination of homogeneous mixture of NiO, ZnO, CuO and Mn_2O_3 powders at 900°C for 4 h and subsequently combined planetary and agate milling. Phase composition and morphology of the manganite powder were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Disk-shaped compacts were fabricated by uniaxial pressing at 0.2GPa and sintered at temperatures between 1100 and 1250°C for 2 h. The effects of sintering temperature on density, microstructure and DC electrical resistance were evaluated. Temperature-dependent resistance measurements performed in the range from −30 to 120°C yielded a thermistor constant of B = 2352K. The energy band gap, estimated from the reflectivity knee, was 0.56 eV. Furthermore, a thick-film paste was formulated from the synthesized manganite powder and used to fabricate segmented NTC thermistors. Electrical and thermal measurements, including sheet resistance, confirmed their suitability for further sensor applications.