Mercury disilver tetraiodide (Ag2HgI4)
In its low temperature form, Ag2
adopts an ordered structure (a) in which the Ag+
ions occupy some of the tetrahedral sites in the structure. At high temperatures, structure (b) is adopted, there are more sites in the structure than there are ions (Ag+
) present. As a result, the conductivity increases as the ions are more mobile and the I-
ions are easily polarizable.