  With the help of Monte Carlo simulations and a mean-field theory, we
investigate the ordered steady-state structures resulting from the motion of a
single vacancy on a periodic lattice which is filled with two species of
oppositely ``charged'' particles. An external field biases particle-vacancy
exchanges according to the particle's charge, subject to an excluded volume
constraint. The steady state exhibits charge segregation, and the vacancy is
localized at one of the two characteristic interfaces. Charge and hole density
profiles, an appropriate order parameter and the interfacial regions themselves
exhibit characteristic scaling properties with system size and field strength.
The lattice spacing is found to play a significant role within the mean-field
theory.
