  Charged dilatonic black hole (BH) has rather rich phase diagrams which may
contain zeroth-order, first-order as well as reentrant phase transitions (RPTs)
depending on the value of the coupling constant $\alpha$ between the
electromagnetic field and the dilaton. We try to give a microscopic explanation
for these phase transitions by adopting Ruppeiner's approach. By studying the
behaviors of the Ruppeiner invariant $R$ along the co-existing lines, we find
that the various phase transitions may be qualitatively well explained as a
result of two competing factors: the first one is the low-temperature effect
which tends to shrink the BH and the second one is the repulsive interaction
between the BH molecules which, on the contrary, tends to expand the BH. In the
standard phase transition without RPT, as temperature is lowered, the first
kind of factor dominates over the second one, so that large black hole (LBH)
tends to shrink and thus transits to small black hole (SBH); While in the RPT,
after the LBH-SBH transition, as temperature is further decreased, the strength
of the second factor increases quickly and finally becomes strong enough to
dominate over the first factor, so that SBH tends to expand to release the high
repulsion and thus transits back to LBH. Moreover, by comparing the behavior of
$R$ versus the temperature $T$ with fixed pressure to that of ordinary
two-dimensional thermodynamical systems but with fixed specific volume, it is
interesting to see that SBH behaves like a Fermionic gas system in cases with
RPT, while it behaves oppositely to an anyon system in cases without RPT. And
in all cases, LBH behaves like a nearly ideal gas system.
