Additional polymorphism and non-stoichiometry in AgF

A phase forming from B2 type AgF on decrease of pressure found recently by Vaidya and Kennedy has been studied by in situ X-ray diffraction. It is indexed as hexagonal with c = 6.226±0.45 Å and a = 3.246±.002 Å, Z = 2. This structure is probably inverse NiAs. Its pressure of formation is highly dependent on the samples history of pressure variation. All three phases, B1, B2 and hexagonal have been made to give X-ray patterns with each line split into two lines of equal intensity. We interpret this as a decomposition into two non-stoichiometric phases, one Ag rich and the other F rich. The conditions for the formation of these split phases are not always reproducible which suggests that this is a metastable phenomenon possibly due to pressure gradients on the sample. The splitting could, however, also be explained by equilibrium behavior.