What is the crystal structure of copper iodide?

Copper iodide, characterized by a direct wide band-gap and a good lattice matching with Si, is an intrinsic p-type I-VII compound semiconductor. It shows remarkable optoelectronic properties, including a large exciton binding energy at room temperature and a very small piezoelectric coefcient. The major obstacle to its application is the difculty in growing a single-crystal epitaxial flm of cuprous halides.

Cuprous iodide, a potential laser modulator material, has been grown from hydriodic acid solution by the slow decomposition of the CuI·HI complex. Emission spectrographic analysis demonstrated that the crystals produced are considerably purer than the starting material.

Copper iodide (CuI), as a non-layered I-VII group compound, crystallizes into three different phases: α, β, and γ and shows different crystal lattices with increasing temperature. CuI under- goes a phase transition from the cubic γ-phase to the hexagonal β-phase above 369 °C. The crystal lattice of the β and γ-phasebeing hexagonal and cubic respectively whereasthat of the α-phase unknown yet.

Reference:

[1]Zhixing Fu. “Cuprous Iodide Pseudopolymorphs Based on Imidazole Ligand and Their Luminescence Thermochromism.” Crystal Growth & Design 16 4 (2016): 2322–2327.

[2]John J. O’Connor,  Alton F. Armington. “Preparation and properties of cuprous iodide.” Materials Research Bulletin 6 8 (1971): Pages 765-769.

[3]D Ahn. “Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes.” Scientific Reports (2020): 3995.