Abstract
We report on the infrared absorption spectra of three oxides where charged
superlattices have been recently observed in diffraction experiments. In
La$_{1.67}$Sr$_{0.33}$NiO$_4$, polaron localization is found to suppress the
low-energy conductivity through the opening of a gap and to split the
$E_{2u}$-$A_{2u}$ vibrational manifold of the oxygen octahedra. Similar effects
are detected in Sr$_{1.5}$La$_{0.5}$MnO$_4$ and in La$_2$NiO$_{4+y}$, with
peculiar differences related to the type of charge ordering.