Local structural properties of CuI at low temperatures.

This study examined the local structural properties of CuI at low temperatures of 10-300 K by x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) measurements at the Cu K edge. The XRD data were refined using two models, split (distorted zinc-blende structure) and non-split (zinc-blende structure), using a conventional Rietveld refinement combined with a maximum entropy method (MEM). MEM/Rietveld analyses showed that both the split and non-split models could fit the data. EXAFS revealed the split model fit to be better than the non-split model. The split distance of Cu-I pairs was approximately 0.03 Å at 15 K and increased to 0.07 Å at 300 K. XRD and EXAFS combined together suggested that the CuI crystal was in a metastable state with a distorted zinc-blende structure at low temperatures.