  The ion-ion interactions become exponentially screened for ions confined in
ultranarrow metallic pores. To study the phase behaviour of an assembly of such
ions, called a superionic liquid, we develop a statistical theory formulated on
bipartite lattices, which allows an analytical solution within the
Bethe-lattice approach. Our solution predicts the existence of ordered and
disordered phases in which ions form a crystal-like structure and a homogeneous
mixture, respectively. The transition between these two phases can potentially
be first or second order, depending on the ion diameter, degree of confinement
and pore ionophobicity. We supplement our analytical results by
three-dimensional off-lattice Monte Carlo simulations of an ionic liquid in
slit nanopores. The simulations predict formation of ionic clusters and ordered
snake-like patterns, leading to characteristic close-standing peaks in the
cation-cation and anion-anion radial distribution functions.
