High phase-transition temperature for β-AgI to α-AgI and an explanation of the memory effect

The AgI thermal transition of the {β} phase (wurtzite structure) to the {α} phase (body-centered-cubic structure) occurred at a higher temperature (162 ^∘{}C) than that previously reported ({~}147 ^∘{}C). It is believed that this higher temperature is the result of these gelatin-grown {β}-phase microcrystals being unusually free of included {γ} phase and other crystal defects that would serve as {α}-phase nucleation sites. Introducing defects into these grains catalyzed this transition at the lower temperature. Having two distinct phase-transition temperatures explains the memory effect that has been reported in some AgI microcrystalline samples.