  Considering the long range Coulomb interactions between large polarons in
dielectrics, we propose a model for their crystallization when no bipolarons
are formed. As the density increases, the melting is examined at $T=OK$. One
possibility is the delocalization towards a liquid state of polarons. However,
we show that this cannot happen if the electron-phonon coupling is larger than
some critical value. The other competing mechanism is the dissociation of the
polarons themselves, favored owing to their large mass at strong coupling.
Finally, we propose a phase diagram for the insulator-to metal transition as a
function of the density and electron-phonon coupling.
