  We argue that an ionic lattice surrounded by a Fermi liquid changes phase
several times under pressure, oscillating between the symmetric phase and a
low-symmetry dimerized structure, as a consequence of Friedel oscillations in
the pair potential. Phase oscillations explain the tendency towards
dimerization which has been recently reported for the light alkali metals under
high pressure. Moreover, a restoring of the symmetric phase is predicted for
such elements at an even higher density.
