Effect of Oxygen Partial Pressure during Firing on Electrical Properties of Sintered Body Composed of Mn1.5CoNi0.5O4

Abstract

The effect of PO2 during the oxidation of a sintered body with a molar ratio of Mn:Co:Ni=3:2:1 on conversion into a cubic spinel-type oxide was investigated. Moreover, the electrical properties of the sintered body with a monophase cubic spinel structure were evaluated in atmospheres with various PO2 values. A sintered body of monophase spinel-type oxide, Mn1.5CoNi0.5O4, was successfully obtained by heating a mixture of nitrates at 1400°C in argon, followed by cooling to 1100°C and holding at that temperature for over 168 h at PO2 =0.40 atm, or for over 48 h in the PO2 range from 0.55 to 1.00 atm. The electrical conductivity, σ, of the specimens oxidized at PO2 of 0.40 to 1.00 atm increased exponentially with increasing temperature. In the region of 0.40≦PO2 (atm)≦0.85, σ increased with increasing PO2 . All of the specimens oxidized at PO2 of 0.40 to 1.00 atm revealed p-type semiconductor properties, because the Seebeck coefficients were all positive. The PO2 dependence of σ was thought to be dependent on the existence ratio of Mn3+ to Mn4+ in octahedral sites. The conduction was considered to be controlled by a small polaron hopping mechanism.