In situ XAFS and XRD studies of pressure-induced local structural change in liquid AgI

In order to examine the pressure-induced structural change of liquid silver iodide ( AgI), high-pressure and high-temperature in situ x-ray absorption fine structure ( XAFS) and x-ray diffraction ( XRD) studies have been carried out up to 1200 K and 6 GPa. The modifications in the x-ray absorption near edge structure ( XANES) spectra and x-ray structure factors, S( Q), with increasing pressure provide evidence for changes in the short-range order of liquid AgI. The I - Ag bond length in liquid AgI increases by compression up to 2 GPa, which proposes that components with higher coordination than fourfold are introduced. The I - Ag bond length decreases monotonically with compression above 2 GPa, indicating that the structural change involving a coordination-number change is completed below 2 GPa and then a high-pressure form of liquid AgI is stabilized. Comparing the I - Ag bond lengths of liquid AgI with those of crystalline phases, we conclude that the high- pressure form of liquid AgI has a rocksalt-like structure with large vacancies.