  Superconductivity has been found in the iron-arsenides with different
structures by alternative stacking of the conducting Fe2As2 layers and spacer
layers including alkali- or alkali-earth metal ions and PbO- or perovskite-type
oxides blocks. So far, no spacer layer could be intercalated in between the
neutral Fe2Se2 layers similar in structure to Fe2As2 layers except for
alkali-metal ions in AxFe2-ySe2. The superconducting phase in AxFe2-ySe2 with
transition temperature of 32 K is always inter-grown with the insulating phase
which exhibits an antiferromagnetic order with extremely high Neel temperature
of ~560 K and the order of Fe vacancies. Such inhomogeneity makes the
investigation on the underlying physics in AxFe2-ySe2 complicated. Here we
report the synthesis of a novel superconductor LiFeO2Fe2Se2 by hydrothermal
method, exhibiting superconductivity at ~43 K, in which anti-PbO-type spacer
layers of LiFeO2 have been successfully intercalated between anti-PbO-type
Fe2Se2 layers. This finding demonstrates that superconductivity can be realized
in the iron selenide with a novel spacer layer of anti-PbO-type, which is not
found in the iron arsenides, and expands the category of the iron-based
superconductors. Such a new synthetic method paves a new way to search for
possible novel superconductors with different spacer layers, which is helpful
to further study the underlying physics in iron-based high-Tc superconductors.
