Preparation and electrical properties of monophase cubic spinel, Mn_1.5Co_0.95Ni_0.55O₄, derived from rock salt type oxide

Abstract

The purpose of this study was to prepare a sintered body consisting of monophase cubic spinel type oxide, Mn_1.5Co_0.95Ni_0.55O₄, and to evaluate its electrical properties. It was found that cooling from 1400 to 1000 °C in nitrogen did not affect the preservation of the sintered rock salt type oxide formed at 1400 °C. A crack free sintered body of monophase cubic spinel may be obtained by heat treatment at 1000 °C in air, using a specimen cooled from 1400 °C at a rate of 500 °C min ⁻¹. A heat treatment time in air at 1000 °C of more than 48 h was required to convert the rock salt type structure into a perfect cubic spinel structure. The electrical conductivity, δ, of the sintered cubic spinel oxide synthesized in this work was found to be stable at 100 and 200 °C in air and at 100, 200 and 300 °C in nitrogen. The sintered spinel oxide was a p-type semiconductor, based on small polaron hopping conduction. The intrinsic hole concentration, n, was estimated to be constant, with a value of 1.6–1.8×10²⁸m⁻³. The mobility, μ, increased exponentially with increasing annealing temperature in both atmospheres, suggesting that the change in δ is dependent on μ.