  The perovskite-type iron oxide Sr$_{2/3}$La$_{1/3}$FeO$_3$ is known to show
characteristic spin-charge ordering (SCO), where sixfold collinear spin
ordering and threefold charge ordering are coupled with each other. Here, we
report the discovery of a spin-charge decoupling and an antiferromagnetic (AFM)
state competing with the SCO phase in perovskites
(Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$. By comprehensive measurements
including neutron diffraction, M$\"{o}$ssbauer spectroscopy, and x-ray
absorption spectroscopy, we found that the isovalent Ba$^{2+}$ substitution
systematically reduces the critical temperature of the SCO phase and
additionally yields the spin-charge decoupling in $x$ > 0.75. Whereas the
ground state remains in the SCO phase in the whole $x$ region, an unexpected
G-type AFM phase with incoherent charge ordering or charge fluctuation appears
as the high-temperature phase in the range of $x$ > 0.75. Reflecting the
competing nature between them, the G-type AFM phase partially exists as a
metastable state in the SCO phase at low temperatures. We discuss the origin of
the spin-charge decoupling and the emergence of the G-type AFM phase with
charge fluctuation in terms of the bandwidth reduction by the Ba substitution.
