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Madelung Energy, Coulomb Interaction, Elpasolite For binary ionic compounds the Madelung energy can be calculated using the Madelung constant, the ionic charges and the next neighbour distance of the ions only. For ternary and higher systems the well-known standard formula cannot be applied, because the ionic charges and distances combine in different ways. In the present work we calculate the Madelung energy of the quaternary elpasolite structure by straightforward computer summation and propose a Madelung function which describes the Madelung energy in dependence on the lattice constant and the free structural parameter. This function has been applied to several chemical compounds of the elpasolite type to determine the individual Madelung energy.

The F:O ratio in homogeneous and inhomogeneous rare earth oxide fluoride systems of compositions RO(1+x)F(1-2x) with -0.1