Electrical and Crystallographic Studies of the System Cu_xNi_1−xMn₂O₄

Abstract

Electrical and crystallographic properties of the system Cu_xNi_1−xMn₂O₄ have been studied. The negative deviation of lattice parameters from Vegard’s linearity rule indicates that CuMn₂O₄ is a normal cubic spinel. The electrical resistivity temperature-behaviour obeys the relation (Remark: Graphics omitted.), and the value of activation energy (ΔE) for conduction in NiMn₂O₄ remains constant even after addition of 50 mole percent CuMn₂O₄. The thermoelectric power of NiMn₂O₄ changes sign from negative to positive by an addition of 20 mole percent CuMn₂O₄. It is concluded that in CuMn₂O₄ the Cu is present predominantly in Cu²⁺ valence state along with a small number of Cu¹⁺ ions at tetrahedral sites. The electrical conduction in this system seems to take place through hopping of charge carriers between Mn³⁺ and Mn⁴⁺ ions at octahedral sites. A contribution to electrical conduction from tetrahedrally located Cu²⁺ and Cu¹⁺ ions has also been considered.