Effect of Fe incorporation on cation distributions and hopping conductions in Ni-Mn-Co-O spinel oxides

Effect of Fe incorporation on electrical properties of (NixCoyMn3-x-y)O4 (NMC) spinel compound is investigated for the application to a negative temperature coefficient (NTC) thermistor. Cation distribution of the Fe doped NMC (FNMC) is calculated based on the size of ions located at tetragonal A sites and octahedral B sites in spinel structure, which can be closely related with temperature dependent electrical properties of the FNMC. With change of Fe contents, the ratio of Mn3+/Mn4+ in octahedral B site of FNMC is changed which can determine the temperature sensitivity factor (B-value). Hopping conduction mode relating with activation energy and hopping distance was also discussed depending on Fe contents, based on the small polaron hopping theory. •Hopping mode in FNMC occurs through nearest neighboring hopping (NNH) motion when Fe content increases above 0.5.•Variable range hopping (VRH) motion was determined as hopping conduction mechanism for FNMC with Fe content lower than 0.5.•Cation distribution in FNMC with different Fe content is proposed based on the theoretical model.