  We investigate the interplay of electron-phonon (EP) coupling and strong
electronic correlations in the frame of the two-dimensional (2D) Holstein t-J
model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled
band case. The use of direct Lanczos diagonalization on finite lattices allows
us to include the effects of quantum phonon fluctuations in the calculation of
spin/charge structure factors and hole-phonon correlation functions. In the
adiabatic strong coupling regime we found evidence for ``self-localization'' of
polaronic carriers in a $(\pi,\pi)$ charge-modulated structure, a type of
superlattice solidification reminiscent of those observed in the nickel
perovskites $La_{2-x}Sr_{x}NiO_{4+y}$.
