  Mixtures of near-symmetric oppositely charged components with strong
attractive short range interactions exhibit ordered lamellar phases at low
temperatures. In the strong segregation limit the state of these systems can be
described by the location of the interfaces between the components. It has
previously been shown that these systems are stable against small deformations
of the interfaces. We examine their stability in the presence of a uniform
electric field. When the field is perpendicular to the lamellae, the system is
unstable against long wavelength deformations for all non-zero values of the
external field. A field parallel to the lamellae produces deformed but
persistent interfaces. In a finite thickness system, onset of an external
perpendicular field modifies the ground state. Flow between the old and new
ground states requires the destruction of the original interfaces; this
destruction proceeds through the instabilities identified in the bulk case. We
examine the possibility of dynamical stabilization of structures by means of
oscillating fields.
