Structure and dynamics of molten aluminium and gallium trihalides

Abstract

Diffraction patterns for molten AlBr₃, GaBr₃ and GaI₃ were measured at temperatures close to their melting points using the time-of-flight neutron diffraction technique at the Intense Pulsed Neutron Source at Argonne National Laboratory. The total structure factors exhibit a peak at Q ⋍ 1·2Å^-1 which is a signature of intermediate-range order in the melt. The derived coordination numbers indicate a tetrahedral coordination in all three melts, consistent with dimeric M₂X₆ molecules being the dominant species. The data for aluminium and gallium bromide are in agreement with reference interaction site model calculations based on complete dimerization, while the gallium iodide appears to be only partly dimerized. These conclusions are supported by Raman scattering results in the literature and those of the present authors.