METAL-AMMONIA SOLUTIONS - A LATTICE MODEL APPROACH

A generalized Falicov-Kimball model is applied to study the phase diag ram of metal ammonia solutions. The model includes a fluid-fluid inter action term and an electron-fluid interaction with a hard core and an attractive tail. Mean-field theories are derived for the localized and delocalized electron phases using ideas from the slave-boson approach to the Hubbard model. The attractive force stabilizes both the homoge neous delocalized electron phase and a regime where the electrons loca lize in cavities devoid of fluid particles. In its absence, the locali zed states are found to be unstable towards phase separation, in contr ast to previous predictions. The Gaussian fluctuations and structure f actors derived from this theory suggest the-existence of bicontinuous channels percolating through the system. These findings agree qualitat ively with experiments and computer simulations. (C) 1998 American Ins titute of Physics. [S0021-9606(98)50821-5].