Preparation and Electrical Properties of Sintered Bodies Composed of Monophase Spinel Mn_(2-X)Co_2XNi_(1-X)O₄ ( 0 \LeqX \Leq 1) Derived from Rock-Salt-Type Oxides

Preparation of spinel-type oxides, Mn_(2-X)Co_2XNi_(1-X)O₄ (0≦X≦1), and their electrical properties were investigated. Die-pressed oxides (25 mm diam. ×4 mm), containing metals with desired molar ratios, were heated to 1400° C, and held at that temperature for 3 h in nitrogen. The sintered specimens were quenched to 800° C and then oxidized for 95 h in air to completely convert them into spinel-type oxides. The lattice constants of the spinels decreased with increasing X. Two turning points, at X=0.5 and 0.84, were observed. Based on these results, the cation distributions were estimated. Calculation of the Seebeck coefficient proved that the carriers of the oxides with X=0 and 0.25 are electrons and those of the oxides with X=0.5 to 1 are holes. Activation energies calculated from mobility were 0.34 to 0.36 eV. The conduction was considered to be due to the small polaron hopping mechanism.