Effect of Ag addition on the microstructure and electrical properties of Ni0.6CoMn1.4O4/Ag composite ceramics

•Novel Ni0.6CoMn1.4O4/Ag composite ceramics were successfully fabricated.•The introduced Ag nanoparticles formed heterogeneous interfaces with the NCMO particles.•Space electronic transmission mechanism is proposed to explain the decrease of resistivity. In this work, novel Ni0.6CoMn1.4O4: x wt%Ag (NCMO: Ag-x, x = 0, 5, 7.5, 10, 12.5, and 15) composite ceramics were successfully fabricated by combining chemical reduction with solid-state coordination reaction method. The phase composition, microstructure, element distribution, and electrical properties are systematically investigated. The introduced Ag nanoparticles formed heterogeneous interfaces with the NCMO particles and were uniformly distributed in the samples. Due to the introduction of Ag, the Co2+ content increases from 33.2% to 50.0%. The average valence state of Mn ions increases from 2.91 to 3.17, then it decreases to 2.89. The Ag addition does facilitate the remarkable reduction of room temperature resistivity from 250.38 to 7.61 Ω cm and makes the resistivity drift below 2.57%, while B value decreases from 3145 to 1909 K, which are caused by the decreases of grain resistance and grain boundary resistance. Moreover, space electronic transmission mechanism is also proposed to further explain the positive effect of Ag introduction on electrical properties of the NCMO/Ag composite ceramics.