The normal thiospinel ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ exhibits a temperature-induced metal-insulator $(M-I)$ transition around 230 K with structural transformation, showing hysteresis on heating and cooling. The symmetry changes from a high-temperature cubic phase in a metallic state to low-temperature tetragonal phase in an insulating state. A significant characteristic feature is the absence of localized magnetic moment below $T_{M-I}.$ On the other hand, ${\mathrm{NiIr}}_2{\mathrm{S}}_4$ remains metallic down to 4.2 K without the structural transformation. We have systematically studied the structural transformation and electrical and magnetic properties of ${\mathrm{Cu}}_{1-x}{\mathrm{Ni}}_x{\mathrm{Ir}}_2{\mathrm{S}}_4.$ The variation of the metal-insulator transition with Ni concentration x is presented. A phase diagram between $T_{M-I}$ and x will be provided for the ${\mathrm{Cu}}_{1-x}{\mathrm{Ni}}_x{\mathrm{Ir}}_2{\mathrm{S}}_4$ system. The $T_{M-I}$ varies drastically from 226 to 88 K with x from 0.00 to 0.13 and disappears around $x=\mathrm{0.15.}\mathrm{}$ For $0.08<~x<~0.13,$ the cubic and tetragonal phases coexist below $T_{M-I}.$ For a high-temperature metallic phase, the value of the Pauli paramagnetic susceptibility increases monotonically with x, which shows $dD\left(\varepsilon \right)/d\varepsilon <0\mathrm{}$ at the Fermi energy ${\varepsilon }_F,$ through the decrease of the free-electron number density, where $D\left(\varepsilon \right)$ is the electronic density-of-state on the basis of a nearly free-electron model. By the introduction of a Ni ion to the A-site of ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ in the spinel structure, whether the localized magnetic moment below $T_{M-I}$ arises or not will be discussed.

• Received 8 February 2001

DOI:https://doi.org/10.1103/PhysRevB.64.075106