  We study possible charge instabilities in doped Mott insulators by employing
the two-dimensional t-J model with a positive value of the next
nearest-neighbor hopping integral t' on a square lattice, which is applicable
to electron-doped cuprates. Although the d-wave charge density wave (flux
phase) and d-wave Pomeranchuk instability (nematic order) are dominant
instabilities for a negative t' that corresponds to hole-doped cuprates, we
find that those instabilities are strongly suppressed and become relevant only
rather close to half filling. Instead, various types of bond orders with
modulation vectors close to (pi,pi) are dominant in a moderate doping region.
Phase separation is also enhanced, but it can be suppressed substantially by
the nearest-neighbor Coulomb repulsion without affecting the aforementioned
charge instabilities.
