A study of Co_3-xNi_xO₄(O ≤x ≤ 1) system

Abstract

A series of solid solutions of composition Co_3-xNi_xO₄ 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 around x=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 [Ni_x^IIICo_2-x^III]₀O₄ for the solid solutions which permits formation of σ*(e_g) band through strong covalent interaction between octahedral-site low spin Co^III/Ni^III and oxide ion in the spinel structure.