Study of local structure and ion dynamics in GdCl3 - Gd2O3 and KCl - GdCl3 - Gd2O3 melts: In situ Raman spectroscopy and ab initio molecular dynamics

The local structure and dynamics of ions in homogeneous GdCl3-Gd2O3 and KCl-GdCl3-Gd2O3 oxide-chloride melts with a gadolinium oxide concentration up to 6 mol% were studied using in situ Raman spectroscopy and ab initio molecular dynamics. Quantitative and qualitative changes in the spectral characteristics of homogeneous oxide-chloride melts compared with GdCl3 and GdCl3-KCl melts were observed. These comprised additional low-intensity vibrational bands appearing at 208, 371 and 202, 368 cm(-1), respectively. No gadolinium oxide bands were detected, indicating dissociation in the chloride melt. Molecular dynamics simulations showed that oxygen in melts is adjacent to three gadolinium ions, with an inter-ionic O-Gd distance of 22 A. The [Gd3O] associate, in turn, is incorporated into the network-like structure of the original chloride melt. As a result of this association, ion transport through the melt is hampered, as substantiated by the calculated self-diffusion coefficients. (C) 2020 Elsevier B.V. All rights reserved.