Preparation And Electrical Properties Of The Negative Temperature Coefficient Thermistor

Mn-based transition-metal spinel oxide ceramics are widely used as negative temperature coefficient (NTC) thermistors for temperature measurement and control, compensation and suppression of inrush current, due to their high sensitivity to temperature change, high stability and reliability and low price. It is generally accepted that their conduction of electrons in these ceramics is described by a thermally activated phonon-assisted hopping of charge carriers of differing oxidation states on the octahedral sites of spinel structure, namely, the small polaron model. The specific resistivity of these ceramics follows the well-known Arrhenius relation: ρ=ρ₀ exp[E_a/kT], in which ρ is the specific resistivity, E_a the activation energy for themigration of charge carriers, k Boltzmann's constant and T absolute temperature. The basic electrical parameters for these ceramics are as follows: the specific resistivity ρ₂₅ at 25℃, the thermal constant B_25/50=E_a/K, the aging coefficient ΔR/R(%).It has been known that the electrical properties of spinel-structured NTC ceramics are mainly dependent on the valents and distributions of the cations between tetrahedral sites and octahedral sites. Also, there are many factors contributing to the valents and distributions of these cations. For example, there are some disputes on the valents and distributions of the copper ions in the Cu-Ni-Mn-O systems. And the mechanism still remains unclear and controversial that the Cu-containing NTC systems have much higher electrical conductivities and aging coefficient.To date, Many available methods have been offered to improve the stability of the NTC thermistors, such as adjusting the morphology of the starting powders, the nature of electrodes, the cationic distribution and the addition of impurities such as B, Si,Ba and Li, but the improvement is limited. In this work, we attempted to prepare a mixed oxalate powder Cu_0.3Ni_0.66Mn_2.04(C₂2O₄)₃.nH₂O by solid-state coordination method, and study the effect of the addition of ZrO₂ on the electrical properties in Cu_0.3Ni_0.66Mn_2.04O₄ ceramic.