Stabilities and cell parameters for phases of the AgI-NH₄I-H₂O system

The density, composition, X-ray powder data, unit-cell parameters, and stability fields are reported for five phases of the AgI-NH₄I-H₂O chemical system. The determinations were made by X-ray powder diffraction but with some aid from polarizing optical microscopy. Provisional cell assignments are: phase A_n (4AgI.NH₄I) is cubic, phase B_n (3AgI.NH₄I.6H₂O) monoclinic, phase C_n (AgI.2NH₄I) orthorhombic, phase En (AgI.2NH₄I.H₂O) orthorhombic, and phase F_n (2AgI.NH₄I.2H₂O) monoclinic. Upon combustion of an acetone solution of silver iodide and ammonium iodide, phase A_n forms and, when injected into the atmosphere, transforms to phases F_n or B_n as determined by the available moisture and temperature.