Influence of cation substitution on electrical conductivity of the n-type Cu xIn yCr zSe 4 spinels

Abstract

The single-crystal X-ray diffraction studies have shown that indium ions admixed with CuCr 2Se 4 may locate both in tetra- and octahedral sites of the spinel structure. This property has strong impact on electrical conductivity of the compounds under study. It appeared that octahedral coordination of In 3+ ions leads to metallic conduction, while tetrahedral coordination of In causes semiconducting properties. The thermopower measurement revealed that all samples show n-type conduction in the temperature range 290–480 K. In Cu[Cr 1.38In 0.62]Se 4 a collective electron behaviour in the unfilled of the lowest Cr 3+ Mott-Hubbard sub-band of 3d 3 t 2g band is observed, while in (Cu 0.46In 0.54)Cr 2.08Se 4 a hopping process involving a transfer of electrons from Cr 2+ to Cr 3+ takes place.