Preparation and electrical properties of sintered oxides composed of Mn1.5Co(0.25+x)Ni(1.25-x)O4(0≤x≤0.75) with a cubic spinel structure

Monophase cubic spinel-type oxides of Mn1.5Co(0.25+X)Ni(1.25-X)O4 (\[0 \leqq X \leqq 1\]) were prepared through the oxidation of specimens sintered at 1400 °C. The oxides with \[ 0 \leqq X \leqq 0.75 \] composition are focused on in this study, as the oxides with \[ 0.75 < X \leqq 1 \] composition did not convert into a monophase cubic spinel structure. The electrical conductivity of the sintered bodies was confirmed to increase exponentially with increasing temperature. In the composition range of \[0 \leqq X \leqq 0.75\], both the electrical conductivity and the Seebeck coefficient increased with increasing X. The oxides with composition between \[0 \leqq X < 0.57\] were n-type semiconductors, whereas those with \[ 0.57 < X \leqq 0.75 \] were p-type. It was concluded that electrical conduction in the specimens is controlled by small polaron hopping.