Metal-insulator transition and superconductivity in the spinel-type $\mathrm{Cu}({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{S}}_4$ system

The normal thiospinel ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ exhibits a temperature-induced metal-insulator $\left(M-I\right)$ transition around 226 K with structural transformation, showing hysteresis on heating and cooling. It has been verified that d electrons of Ir atom on the octahedral B sites have a significant role for the $M-I$ transition. On the other hand, ${\mathrm{CuRh}}_2{\mathrm{S}}_4$ is a superconductor with the transition temperature $T_c=4.70\mathrm{}\hspace{0.5em}\mathrm{}\mathrm{K},$ which is well understood on the basis of the BCS theory. It is important to investigate the effect on the $M-I$ transition by substitution of Rh for Ir. We have systematically studied structural transformation and electrical and magnetic properties of $\mathrm{Cu}({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{S}}_4.$ The features of the $M-I$ transition change with Rh concentration x. A phase diagram of temperature versus x will be proposed for the $\mathrm{Cu}({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{S}}_4$ system. The sharp $M-I$ transition temperature varies drastically from 226 to 93 K with x from 0.00 to 0.17 and disappears around $x=\mathrm{0.20.}\mathrm{}$ In a region of $0.00<~x<~0.20,$ the magnetic susceptibility begins decreasing at a constant onset temperature 226 K on cooling process and shows rather broad temperature variation, even though the metallic state is kept in the resistivity. The sharp $M-I$ transition can take place after the suppression of magnitude in the susceptibility has sufficiently developed far below 226 K. These experimental results are discussed with emphasis on the intrinsic difference between $\mathrm{Cu}({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{S}}_4$ and ${\mathrm{CuIr}}_2({\mathrm{S}}_{1-x}{\mathrm{Se}}_x{)}_4$ systems. Furthermore, we will mention the superconductivity for both systems of $\mathrm{Cu}({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{S}}_4$ with high-Rh concentration region and