Short- and intermediate-range order in molten metal tribromides: a computer simulation study

Molecular dynamics simulation studies were performed on four molten metal tribromides, MBr3, M = La, Cc, Y,Dy. The many-body (polarizable-ion) simulation potentials were constructed from recent metal trichloride potentials using physically transparent scaling arguments to account to the change in anion size and polarizability. Comparison was made with neutron scattering results by constructing the total structure factors from the simulated partial functions. In addition, difference functions, which exploit the proposed isomorphous nature of the (Dy, Y) and (La, Cc) pairs, are constructed and compared with experiment. The structural comparison between different trihalide materials is further extended by producing model structure factors, obtained by re-weighting and scaling the simulated partial structure factors for the tribromides, which are then compared with experimental structure factors for certain trichlorides and tri-iodides. Strong structural similarities are demonstrated between the different halides with similar cation-anion radius ratios. It is further suggested that the structures exhibited by the trihalides fall into a small number of characteristic structure classes. The short- and intermediate-range order within the different structure classes is then exemplified by analysis of the local coordination environments and the connectivity of the coordination polyhedra.