Effect of annealing at oxygen partial pressure on the conductivity of Ni 0.5 Mn 2.5 O 4 oxides

This paper presents a study of the electrical properties of nickel manganite Ni 0.5 Mn 2.5 O 4− x as a function of annealing at oxygen partial pressure. The crystalline phase of manganite ceramics during annealing at oxygen partial pressure was investigated using X-ray diffraction; the predominant phase was tetragonal spinel. The electrical properties were analyzed by measuring resistance–temperature characteristics. The activation energy for electron hopping, determined using the slope of the ln ρ –1/T plots, was higher for samples annealed at lower oxygen partial pressure. The Mn 4+ /Mn 3+ ratio, obtained through differential thermal analysis, increased with an increase in the oxygen partial pressure during annealing. The relationship between resistivity and the Mn 4+ /Mn 3+ ratio during annealing at oxygen partial pressure was investigated.