The structure of liquid AlCl 3 and structural modification in AlCl 3 -MCl (M=Li, Na) molten salt mixtures

The scattering from pure liquid AlCl 3 and AlCl 3 -MCl (M=Li, Na) binary molten salt mixtures has been measured by time-of-flight neutron diffraction. Reverse Monte Carlo simulation of the AlCl 3 data whilst confirming a regular tetrahedral local geometry for the Al 3+ ion, challenges the accepted view of the structure as consisting (predominantly) of discrete Al 2 Cl 6 dimers. The data for the mixtures suggest that the connectivity in the structure of pure AlCl 3 , formed by Al-Cl-Al bridges, is proportionately reduced upon the addition of alkali halide as isolated AlCl 4 - units are created. In addition, a gradual shift in the position of the first sharp diffraction peak to higher Q is observed, implying a systematic reduction in the length scale of intermediate-range order. The findings for the mixtures are generally consistent with those from previous structural studies using X-ray diffraction and also with Raman and electrochemical measurements.