Structural and electrical studies of Ni- and Co-substituted Mn<inf>3</inf>O<inf>4</inf>

In this research, we report the structure, microstructure and conduction mechanism study of nickel and cobalt co-substituted Mn3O4 with systematic variation in cobalt concentration. Co-substituted Mn3O4 was prepared by coprecipitation technique in an aqueous solution of metal nitrates and ammonia. X-ray diffraction study of nickel and cobalt co-substituted Mn3O4 established the pure and single-phase formations crystallized in tetragonal crystal symmetry. The overall crystallite size estimated by the Scherrer equation was ~ 30 nm to 50 nm after calcination whereas it was ~ 52 nm to 177 nm after sintering. The microstructure analysis was performed from a scanning electron microscope, and the average grain size was estimated between 2.6 µm to 7.8 µm. The DC conductivity of the substitute Mn3O4 was measured between 300 °C and 720 °C using the two-probe technique. The temperature-dependent resistivity measured for all co-substituted Mn3O4 samples showed decreasing resistivity trend confirming the negative temperature coefficient of resistance behavior. The increase in activation energy as a function of Co concentration was attributed to Verwey and de Bohr hopping mechanism.