Structure of molten trivalent metal chlorides studied by using neutron diffraction:: the systems TbCl3, YCl3, HoCl3 and ErCl3

The total structure factors of the molten trivalent metal chlorides MCl3, where M denotes Tb, Y, Ho or Er, were measured by using neutron diffraction. All four salts melt with a small volume change of less than or equal to 5% from structures comprising MCl63- octahedra to form liquids which show intermediate-range ionic ordering as manifest by a first sharp diffraction peak at approximate to 1 Angstrom(-1) that moves to smaller scattering vector values with decreasing cation size. In the liquid state, the M-Cl distances are comparable with the sum of the ionic radii and the results are consistent with the existence of distorted MCl63- octahedral units. The implications of the results for a polarizable ion interaction model used in recent molecular dynamics calculations are briefly discussed.