The investigation of Zn content on the structure and electrical properties of Zn x Cu0.2Ni0.66Mn2.14−x O4 negative temperature coefficient ceramics

Abstract

The effects of Zn content on the structure and electrical properties of Cu–Ni–Mn–O based negative temperature coefficient thermistors were investigated. Series of Zn x Cu0.2Ni0.66Mn2.14−x O4 (0 ≤ x ≤ 1) ceramics were prepared by Pechini method. Cu2p3/2 X-ray photoelectron spectra demonstrate that Cu+ and Cu2+ ions at A sites decrease with increase of x, and all the Cu ions exist as Cu2+ (B) at x of 1.0 due to the almost exclusive occupation of Zn ions at A sites. X-Ray diffraction spectra show that a single cubic spinel structure is formed at a low Zn content (x ≤ 0.6), and NiO and CuO start to appear at x of 0.8. The segregation of NiO at x ≥ 0.8 is caused by the migration of Cu ions for A to B sites. With Zn content x increasing from 0 to 1.0, the electrical resistivity increases from 42 to 980 Ω cm which can be attributed to the decrease of the electrical conduction caused by Cu ions at A sites. The resistivity drift decreases sharply from 12.6 to 4.2% with increasing x from 0 to 0.4, and the value is only 0.16% at x of 1.0.