Structural and electrical properties of MgO-doped Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 (0 < = x < = 0.25) NTC thermistors

摘要

We have prepared polycrystalline Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 (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 Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 samples increased, both the grain size and density decreased. The as-sintered Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 samples contained Mn- and Ni-rich phases with cubic spinel structure. The MgO-doped Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 negative temperature coefficient (NTC) thermistors provided various electrical properties, depending on Mg content. The electrical resistivity, S_(25/85) constant, and activation energy of the Mn_(1.4)Ni_(1.2)Co_(0.4-x)Mg_xO_4 NTC thermistors increased with increasing Mg content. The values of rho_(25), S_(25/85) constant, and activation energy of the NTC thermistors were 11,185-20,016 OMEGA cm, 3635-4032 K, and 0.313-0.348 eV, respectively.