A series of solid solutions of composition Co3−xNixO4 has been studied. For 0≤x≤1·1 the members crystallize in the cubic spinel structure Measurements of dc electrical conductivity and Seebeck coefficient show that there is a transition from semiconducting state to semi-metallic state aroundx=0·5–0·6. All compositions withx>0·5 are semimetallic and ferrimagnetic. The results have been rationalised on the basis of the cation distribution (Co2+)t [NixIIICo2−xIII]0O4 for the solid solutions which permits formation of σ*(eg) band through strong covalent interaction between octahedral-site low spin CoIII/NiIII and oxide ion in the spinel structure.
Volume 134, 2022
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