Local structural aspects of the metal-insulator transition in CuIr$_{2}$S$_{4}$ from total scattering x-ray study

A thiospinel CuIr$\bf _{2}$S$\bf _{4}$ exhibits a metal-insulator (MI) transition at T=230 K, with simultaneous spin-dimerization and charge-ordering [1]. The transition can also be driven by extended exposure to the x-rays at low T [2, 3]. Total x-ray scattering study of CuIr$\bf _{2}$S$\bf _{4}$ was carried out using 100 KeV synchrotron beam and rapid acquisition pair distribution function (RAPDF) approach. The RAPDF results indicate consistency of the local and average structure at high T. At 100 K long x-ray exposure melts the long-range order (LRO) of the dimerization pattern, without affecting the local structure, in agreement with diffuse scattering result [3]. The dependence of the LRO related superlattice peak intensity on the exposure time reveals that the melting occurs within approximately 15 seconds of exposure under experimental conditions used. At 100 K the LRO is recovered without temperature increase quickly after the cessation of the beamtime exposure. Results on Cr doped samples will be addressed as well. [1] P.G. Radaelli {\it et al.}, Nature {\bf 416}, 155 (2002). [2] V. Kiryukhin {\it et al.}, Phys. Rev. Lett. {\bf 97}, 225503 (2006). [3] H. Ishibashi {\it et al.}, Phys. Rev. B {\bf 66}, 144424 (2002). This work is supported by the NSF under grant DMR-0304391. ANL is supported under DOE contract No. DE-AC02-06CH11357.