High-pressure dissociation of silver mercury iodide, Ag2HgI4

High-pressure X-ray diffraction has been used to probe the behavior of the superionic conductor silver mercury iodide (Ag2HgI4) at pressures up to 5GPa and at temperatures from 295 to 370K. Significant changes in the diffraction spectra, indicative of structural transitions, are observed around 0.7 and 1.3GPa across the range of temperatures studied. The change at 0.7GPa is shown to correspond to the dissociation of silver mercury iodide into silver iodide and mercury iodide, i.e., Ag2HgI4->2AgI+HgI2. The second transition, at 1.3GPa, is due to a structural phase transition within HgI2. Rietveld analysis of the diffraction data is used to confirm and refine all the known crystal structures