The structure of molten CuCl, CuI and their mixtures as investigated by using neutron diffraction

Abstract

The structure of molten CuCl, CuI and their mixtures (CuCl)(x)(CuI)(1-x) with x = 0.294, 0.576, 0.801 was studied by using neutron diffraction. The results are discussed by reference to the information that is available on the structure of CuCl and CuI from experiment, theory and computer simulation. The comparison points to a need for more realistic models for the CuCl-CuI system which should take into account the presence of chemical bonds that have been found in CuI by the application of ab initio molecular dynamics methods.

The structure of molten CuCl: Reverse Monte Carlo modeling with high-energy X-ray diffraction data and molecular dynamics of a polarizable ion model

“…1 together with three earlier neutron diffraction structure factors S N (k) reported by Drewitt et al 11 for natural composition of CuCl and by Eisenberg et al 2 for two different isotopic compositions. As in the three S N (k), our A X (k) also shows clear oscillation beyond the main peak at approximately 3.4 Å -1 .…”

“…42 Although the S N (k) by Drewitt et al was measured at a slightly lower temperature (733K rather than 773K for our and Eisenberg's data), we assume that this difference is small for structure factor data. Although the RMC modeling for molten CuCl has already been carried out by McGreevy and Pusztai, 4 our RMC results include new experimental information, because our A X (k) and S N (k) reported by Drewitt et al 11 are measured up to the high-k region.…”

“…The rigid ion model (RIM) is based on the ion pair potential of the Vashishta and Rahman functional form, 19 Cu I / bb = 2.13, the S CuCu (k) contribution to the S N (k) for CuI is very high and S N (k) exhibits a clear prepeak. 9,11,32 In molten AgI, since Ag b = 5.922 fm, and thus 22 Ag I / bb = 1.14, its S N (k) only presents a small maximum. 10,29 In CuCl, because of the lower chloride polarizability and because of 22 Cu Cl / bb = 0.65, the small shoulder can hardly be distinguished in its S N (k), but it can be appreciated in its A X (k) because of 22 Cu Cl / ff  3.13.…”

“…By using the RIM and PIM described above, we simulated molten CuCl at 773 K, the same temperature as the HEXRD measurements of this work and ND data of Shirakawa et al, 9 and close to the 733 K of ND data of Drewitt et al 11 The ionic density was set as 0.041 ions/Å 3 , 44 (1) up to L/2 instead of . At low k this method gives spurious oscillations due to truncation errors, and therefore we computed S ab (k) directly, up to 4 Å -1 and slightly beyond, by using Eq (2).…”

“…10 In addition, the VR potentials also fail to reproduce the clear sharp prepeak in the experimental S N (k) of molten CuI,. 9,11,28 . More recently, Bitrian et al 29,30,31 showed by MD simulations, that the inclusion of many body interactions due to the induced polarizations of the anions in the VR rigid ion potentials accounts for the small prepeak of molten AgI, as well as the first sharp diffraction peak of molten CuI.…”