Copper(I) iodide, like most binary (containing only two elements) metal halides, is an inorganic polymer.  It has a rich phase diagram, meaning that it exists in several crystalline forms. It adopts a zinc blende structure below 390 °C (γ-CuI), a wurtzite structure between 390 and 440 °C (β-CuI), and a rock salt structure above 440 °C (α-CuI).  The ions are tetrahedrally coordinated when in the zinc blende or the wurtzite structure, with a Cu-I distance of 2.338 Å.  Copper(I) bromide and copper(I) chloride also transform from the zinc blende structure to the wurtzite structure at 405 and 435 °C, respectively. Therefore, the longer the copper–halide bond length, the lower the temperature needs to be to change the structure from the zinc blende structure to the wurtzite structure. The interatomic distances in copper(I) bromide and copper(I) chloride are 2.173 and 2.051 Å, respectively. Consistent with its covalency, CuI is a p-type semiconductor.