The effect of ZnO content and sintering temperature on the electrical properties of Cu-containing Mn 1.95− xNi 0.45Co 0.15Cu 0.45Zn xO 4 (0≤ x≤0.3) NTC thermistors

Abstract

The primary phase of sintered Mn 1.95− x Ni 0.45Co 0.15Cu 0.45Zn x O 4 (0 ⩽ x ⩽ 0.3) bodies was solid solutions of constituent oxides with a cubic spinel structure, along with NiO-rich Mn–Ni–Co–Cu–(Zn)–O oxides and Mn 3O 4. The density and grain size of the Mn 1.95− x Ni 0.45Co 0.15Cu 0.45Zn x O 4 samples increased with increasing ZnO content. The electrical properties of the negative temperature coefficient (NTC) thermistors were controlled by changing their composition. The incorporation of a small amount of ZnO ( x ⩽ 0.12) led to an increase in resistivity and the B 25/85 constant. The values of ρ 25, ρ 85, B 25/85 constant, and activation energy for the NTC thermistors sintered at 1025 °C were somewhat higher than those sintered at 1075 °C. The NTC thermistors with very low resistivities and moderate sensitivities to temperature excursions were fabricated at a wide range of sintering temperature (1025–1075 °C).