  We have studied a simple effective model of charge ordered insulators. The
tight binding Hamiltonian consists of the effective on-site interaction U and
the intersite density-density interaction Wij (both: nearest-neighbor and
next-nearest-neighbor). In the analysis of the phase diagrams and thermodynamic
properties of this model we have adopted the variational approach, which treats
the on-site interaction term exactly and the intersite interactions within the
mean-field approximation. Our investigations of the general case (as a function
of the electron concentration) have shown that the system exhibits various
critical behaviors including among others bicritical, tricritical, critical-end
and isolated critical points. In this report we concentrate on the metastable
phases and transitions between them. One finds that the first- and second order
transitions between metastable phases can exist in the system. These
transitions occur in the neighborhood of first as well as second order
transitions between stable phases. For the case of on-site attraction the
regions of metastable homogeneous phases occurrence inside the ranges of phase
separated states stability have been also determined.
