Structural and electrical properties of NiMgxMn2-xO4 NTC thermistors prepared by using sol-gel derived powders

Structure and electrical properties of NiMgxMn2-xO4 (where x = 0, 0.1, 0.2, 0.3 and 0.4) ceramics prepared by using sol-gel derived powders have been studied. A careful control of the synthesis process enables producing NiMn2O4 phase with spinel structure at a relatively low calcining temperature of 600 deg. C. All compositions showed a linear increase in ln ρ vs. 1/T over the measured temperature range, indicative of negative temperature coefficient (NTC) characteristics. As the concentration of Mg increased from 0.0 to 0.4, the ρ25, B25/85 stability constant and activation energy of NiMgxMn2-xO4 thermistors increased from 4026 to 11,943 Ω cm, 3825-4144 K and 0.329-0.357 eV, respectively. In addition, the ΔR/R value first reduced fleetly from 0.78% to 0.32% and then decreased slowly to 0.12%.