  A combination of neutron diffraction and angle-resolved photoemission
spectroscopy measurements on a pure antiferromagnetic stripe
Rb$_{1-\delta}$Fe$_{1.5-\sigma}$S$_2$ is reported. A neutron diffraction
experiment on a powder sample shows that a 98$\%$ volume fraction of the sample
is in the antiferromagnetic stripe phase with rhombic iron vacancy order and a
refined composition of Rb$_{0.66}$Fe$_{1.36}$S$_{2}$, and that only 2$\%$ of
the sample is in the block antiferromagnetic phase with $\sqrt{5}\times
\sqrt{5}$ iron vacancy order. Furthermore, a neutron diffraction experiment on
a single crystal shows that there is only a single phase with the stripe
antiferromagnetic order with the refined composition of
Rb$_{0.78}$Fe$_{1.35}$S$_2$, while the phase with block antiferromagnetic order
is absent. Angle-resolved photoemission spectroscopy measurements on the same
crystal with the pure stripe phase reveal that the electronic structure is
gapped at the Fermi level with a gap larger than 0.325 eV. The data
collectively demonstrates that the extra 10$\%$ iron vacancies in addition to
the rhombic iron vacancy order effectively impede the formation of the block
antiferromagnetic phase; the data also suggest that the stripe
antiferromagnetic phase with rhombic iron vacancy order is a Mott insulator.
