Abstract
The crystal structure of spinel compound CuIr2S4 was investigated by combination of high-resolution x-ray, electron and neutron diffraction measurements. CuIr2S4 is well known to show metal-insulator (MI) transition accompanied by structural transition at TMI-230 K. The electrical resitivity abruptly increases at TMI, on cooling and the localized magnetic moment vanishes simultaneously. In the present study, the crystal structure below TMI is successfully determined. The results show that CuIr2S4 undergoes a simultaneous charge-ordering and spin-dimerization transition, which can explain the physical properties of CuIr2S4. The charge-ordering pattern consists of isomorphic Ir83++S24 and Ir84++S24. This arrangement is a new description of the spinel structure but much more complex than the known charge-ordering patterns such as stripes.
