Microstructural, electrical and reliability aspects of chromium doped Ni–Mn–Fe–O NTC thermistor materials

A series of Cr2O3-doped Ni–Mn–Fe–O negative temperature coefficient (NTC) ceramic compositions (Ni0.75Mn(2.25−x−y)CrxFeyO4; x = 0.05–0.25 and y = 0, 0.05, 0.25) were prepared by solid-state route. Changes in microstructure and electrical characteristics as a function of dopant concentration was reported. The structural and microstructural features of compositions were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. The change in cation distribution in nickel manganite sublattice due to chromium doping was studied using X-ray photoelectron spectral (XPS) analysis. At sintering temperature 1423 K/3 h, Ni0.75Mn1.95Cr0.25Fe0.05O4 composition shows a maximum B-value and specific resistivity 3954 K and 3118 Ω cm, respectively. The reliability of the compositions was determined by accelerated aging method. The maximum reliability was recorded for 0.25 mol.% Cr2O3 addition, which shows a resistance drift (ΔR) of +0.308%. The excellent reliability of Ni0.75Mn(2.25−x−y)CrxFeyO4 (x = 0.05 to 0.25 and y = 0.05) compositions makes it useful for the development of high performance NTC thermistor devices that requires high reliability.