Structural and electrical properties of MgO-doped Mn1.4Ni1.2Co0.4−xMgxO4 (0 ≤ x ≤ 0.25) NTC thermistors

We have prepared polycrystalline Mn1.4Ni1.2Co0.4−xMgxO4 (0 ≤ x ≤ 0.25) samples using a solid-state reaction process and investigated the MgO doping effect on the microstructure and the electrical properties. It was found that, as the amount of Mg content in the Mn1.4Ni1.2Co0.4−xMgxO4 samples increased, both the grain size and density decreased. The as-sintered Mn1.4Ni1.2Co0.4−xMgxO4 samples contained Mn- and Ni-rich phases with cubic spinel structure. The MgO-doped Mn1.4Ni1.2Co0.4−xMgxO4 negative temperature coefficient (NTC) thermistors provided various electrical properties, depending on Mg content. The electrical resistivity, B25/85 constant, and activation energy of the Mn1.4Ni1.2Co0.4−xMgxO4 NTC thermistors increased with increasing Mg content. The values of ρ25, B25/85 constant, and activation energy of the NTC thermistors were 11,185–20,016 Ω cm, 3635–4032 K, and 0.313–0.348 eV, respectively.