LOCAL COORDINATION AND MEDIUM-RANGE ORDER IN MOLTEN TRIVALENT METAL CHLORIDES - THE ROLE OF SCREENING BY THE CHLORINE COMPONENT

Earlier work has identified the metal ion size R(M) as a relevant para meter in determining the evolution of the liquid structure of trivalen t metal chlorides across the series from LaCl3(R(M) approximate to 1.4 Angstrom) to AlCl3(R(M) approximate to 0.8 Angstrom). Here we highlig ht the structural role of the chlorines by contrasting the structure o f fully equilibrated melts with that of disordered systems obtained by quenching the chlorine component. Main attention is given to how the suppression of screening of the polyvalent ions by the chlorines chang es trends in the local liquid structure (first neighbour coordination and partial radial distribution functions) and in the intermediate ran ge order (first sharp diffraction peak in the partial structure factor s). The main microscopic consequences of structural quenching of the c hlorine component are a reduction in short range order and an enhancem ent of intermediate range order in the metal ion component, as well as the suppression of a tendency to molecular-type states at the lower e nd of the rang R(M).