Effect of Zn substitution on the phase, microstructure and electrical properties of Ni_0.6Cu_0.5Zn_xMn _1.9-xO₄ (0 ≥ x ≥ 1) NTC ceramics

The effect of ZnO addition on the phase composition, morphology, element distribution and electrical properties of Ni_0.6Cu _0.5Zn_xMn_1.9-xO₄ (0 ≥ x ≥ 1) negative temperature coefficient (NTC) ceramics was studied. The ceramics were crystallized in a single cubic spinel structure when x was 0-0.5, Ni-rich rocksalt and CuO impurity phases were detected at x = 0.75, and ZnO formed at x = 1. The SEM and EDS results showed that the sintered bodies contained two types of grain morphologies, one area was rich in Ni and Cu, the other area was rich in Mn and Zn when x 0.75. As the Zn content increased, the electrical resistivities and the B_25/85 constants of the Ni_0.6Cu _0.5Zn_xMn_1.9-xO₄ ceramics increased, and they were 11.33-5442.29 Ω cm and 2395-3301 K, respectively. The resistivity drift decreased sharply from 10.2% to 4.8% when x increased from 0 to 0.25, and it reached the lowest value of 0.02% when x = 0.75. The possible reasons are discussed.