  We study the extended Hubbard model with both on-site (U) and nearest
neighbor (V) Coulomb repulsion using the exact diagonalization method within
the dynamical mean field theory. For a fixed U (U=2.0), the T-n phase-diagrams
are obtained for V=1.4 and V=1.2, at which the ground states of n=1/2 system is
charge-ordered and charge-disordered, respectively. In both cases, robust
charge order is found at finite temperature and in an extended filling regime
around n=1/2. The order parameter changes non-monotonously with temperature.
For V=1.4, phase separation between charge-ordered and charge-disordered phases
is observed in the low temperature and n < 0.5 regime. It is described by an
"S"-shaped structure of the n-/mu curve. For V=1.2, the ground state is
charge-disordered, and a reentrant charge-ordering transition is observed for
0.42 < n < 0.68. Relevance of our results to experiments for doped manganites
is discussed.
