DETERMINATION OF THE STRUCTURE OF BETA-CUI BY HIGH-RESOLUTION NEUTRON POWDER DIFFRACTION

The structure of the beta form of copper(I) iodide has been investigated. The hexagonal beta-Cul exists as a single phase between 647 K and 655 K and shows marked anisotropy in its thermal expansion within this small temperature range. The high quality of the diffraction data has allowed the corrected structure for beta-CuI to be determined in space group P3m1BAR, with I in 2(d) sites at (1/3, 2/3, z) and (2/3, 1/3, z) with z = 0.242(1), thus forming a slightly distorted hexagonal close-packed array. The Cu+ are situated in the tetrahedral voids, predominantly on 2(d) sites at z = 0.6214(8) but with a significant fraction of the cations disordered onto 2(d) sites with z = 0.8786(8). The relationship between this and other previously published structures of beta-CuI is discussed.