Preparation and electrical properties of sintered oxides composed of Mn1.5Co(0.25+X)Ni(1.25-X)O4 ( $$0 \leqq X \leqq 0.75$$ ) 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.