  Ferroelectricity in crystals is associated with the displacement of ions or
rotations of polar units. Here we consider the dipole created by donor doping
($D^+$) and the corresponding bound polaron ($e^-$).A dipole of 6.15 Debye is
predicted, from Berry phase analysis, in the Ruddlesden-Popper phase of ${\rm
Sr_3Ti_2O_7}$. A characteristic double-well potential is formed, which persists
for high doping densities. The effective Hubbard $U$ interaction can vary the
defect state from metallic, a two-dimensional polaron, through to a
zero-dimensional polaron. The ferroelectric-like behavior reported here is
localized and distinct from conventional spontaneous lattice polarization.
