Metal–insulator transition in the spinel-type Cu (Ir1–xTix)2S4 system

Abstract The normal sulphospinel CuIr2S4 exhibits a temperature-induced metalinsulator (M-I) transition around T M-1 = 230 K with a structural transformation. This T M-1 increases markedly with increasing pressure. It has been verified that the 5d electrons of Ir ions at the B sites located at the Fermi surface play a significant role for the strong correlated electron system. Conversely, CuTi2S4 remains metallic down to 4.2 K without any structural transformations. These two compounds have the same normal spinel structure, whereas the number of d electrons at the B sites are quite different. High-purity spinel-type Cu(Iri1−xTix)2S4 specimens have been successfully synthesized. The value of the lattice constant a indicates a broad minimum around x = 0.12, not obeying Vegard's law. We have systematically studied the structural transformation and electrical and magnetic properties of Cu(Ir1−xTix)2S4. A phase diagram between T M-1 and x will be provided for the Cu(Ir1−xTix)2S4 system. T M-1 varies drastically with x and disappears at around x = 0.06. A novel relationship, namely a ‘mirror image effect’, between the value of residual resistivity and the magnitude of the electronic density of states, D(εF), at the Fermi level, has been observed accurately.