Local Ir dedimerization followed by ligand-hole hopping in X-ray irradiated thiospinel

Abstract The extended X-ray-absorption fine structure of a spinel CuIr2(S0.95Se0.05)4 powder sample, which has the charge-ordered temperature T CO = 190 K, was determined at the Ir L 3 edge for a wide temperature range. All the local structure parameters on the Ir–Ir bonds signified the second structural change at T * ~ 70 K. Remarkably, the number of Ir dimers, N D ( T ) , decreased by ~ 10% below T * [ N D ( 0 ) / N D ( T * ) ~ 0.9 ], which indicates partial dedimerization by X-ray irradiation. We also reanalyzed the resistance data of CuIr2S4 [Furubayashi et al., Solid State Comm. 126, 617 (2003)] with the variable-range hopping model by focusing on the density of states at E F , g. The X-ray-induced decrease in resistance was quantitatively explained as a result of the increase in g, which was attributed to the release of holes from the 10%-dedimerized Ir ions. We suppose that the released holes hop over the ligand chalcogen site and discuss the origin of X-ray-induced structural modulations [Kiryukhin et al., Phys. Rev. Lett. 97, 225503 (2006)] in terms of segregation of broken dimers.