THE STRUCTURE OF LIQUID ALCL3 AND STRUCTURAL MODIFICATION IN ALCL3-RACL (M=LI, NA) MOLTEN-SALT MIXTURES

The scattering from pure liquid AlCl3 and AlCl3-MCl (M = Li, Na) binar y molten salt mixtures has been measured by time-of-flight neutron dif fraction. Reverse Monte Carlo simulation of the AlCl3 data, whilst con firming a regular tetrahedral local geometry for the Al3+ ion, challen ges the accepted view of the structure as consisting(predominantly) of discrete Al2Cl6 dimers. The data for the mixtures suggest that the co nnectivity in the structure of pure AlCl3, formed by Al-Cl-Al bridges, is proportionately reduced upon the addition of alkali halide as isol ated AlCl4- units are created. In addition, a gradual shift in the pos ition of the first sharp diffraction peak to higher Q is observed, imp lying a systematic reduction in the length scale of intermediate-range order. The findings for the mixtures are generally consistent with th ose from previous structural studies using x-ray diffraction and also with Raman and electrochemical measurements.