Preparation and characterization of Ni_0.6Co_xMn_2.4−xO₄ (0.2 ≤ x ≤ 1.4) NTC ceramics with low resistivity and high B value

The effects of Co content on the phase structure, micromorphology and electrical performance of Ni_0.6Co_xMn_2.4−xO₄ ceramics were studied using transmission electron microscope (TEM), X-ray powder diffractometer (XRD), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) and resistance/temperature measurements. TEM and high angle annular dark field (HAADF)-mapping results show that the calcined powders were nano-sized and the elements were uniformly distributed. For x < 0.98, the ceramics exhibited single cubic spinel structure. Our SEM–EDS results confirm that a rock-salt phase (Ni,Co)O is formed when 0.98 ≤ x ≤ 1.4. The lattice parameter of the spinel phase decreases with increasing Co content. The room-temperature resistivity of the ceramics decreases from 1100 to 219 Ω cm and then increased to 325 Ω cm as Co was added, while the B value decreased slightly from 3588 to 3030 K. The Ni_0.6Co_xMn_2.4−xO₄ ceramics are promising negative temperature coefficient materials for temperature monitoring in electric vehicles owing to their low resistivity and high B values.