A powder neutron diffraction study of the pressure-induced phase transitions within silver iodide

Powder neutron diffraction measurements of silver iodide are described for pressures up to 5.5 kbar. Three phases have been observed, and the so called intermediate phase which exists in the narrow pressure region from approximately 2.8 to approximately 3.8 kbar has been stabilized with no contamination from neighbouring phases. Isotopically enriched 107 AgI allows the distribution of the ions over the four sites to be determined. The intermediate phase has the anti-litharge structure, with Ag + in 2(a) sites at (0,0,0), ( 1 / 2 , 1 / 2 ,0) and I - in 2(c) sites at (0, 1 / 2 ,z) and ( 1 / 2 ,0,-z). The transformations between this phase and the neighbouring zincblende and rocksalt phases can be described by redistribution of the smaller silver ions, while the iodine sublattice remains largely unchanged.