Ionic Ordering in Thiospinel CuIr$_{2}$S$_{4}$

TL;DR

This study investigates the crystal structure and ionic ordering in CuIr₂S₄ below its metal-insulator transition at 230 K, proposing a model driven by Ir⁴⁺ dimer formation and analyzing temperature-dependent structural changes.

Contribution

The paper presents a structural model for Ir ion ordering in CuIr₂S₄'s insulating phase based on powder X-ray diffraction analysis.

Findings

Ir⁴⁺ and Ir³⁺ ions are ordered in the insulating phase.

Ir⁴⁺ dimers are formed at the transition temperature.

Superstructure spots weaken below 60 K without affecting magnetic or electric properties.

Abstract

Crystal structure of spinel compound CuIr$_{2}$S$_{4}$ was examined by powder X-ray diffraction for the insulating phase below the metal-insulator transition at $T_{MI}$ = 230 K. The superstructure spots are reproduced by considering the displacement of Ir atoms. A model for the ionic ordering of Ir$^{4+}$ and Ir$^{3+}$ with the same number is proposed for the insulating phase on the basis of the structural analysis. The model suggests that the structural change at $T_{MI}$ is driven by the formation Ir$^{4+}$ dimers. In addition, we found that the superstructure spots becomes significantly weak below 60 K, without any significant effects on electric and magnetic properties. Possible mechanism for the transition is discussed.