  Very recently (November, 2010, PRB, 82, 180520R), the first ThCr2Si2-type
ternary superconductor K0.8Fe2Se2 with enhanced TC ~ 31 K has been discovered.
This finding has stimulated much activity in search for related materials and
triggered intense studies of their properties. Indeed, very soon
superconductivity (TC ~ 28-32 K) was also found in the series of related
ternary systems (so-called 122 phases) such as CsxFe2-ySe2, RbxFe2-ySe2,
(TlK)xFeySe2, (TlRb)xFeySe2 etc., which formed a new group of superconducting
iron-based materials without toxic As. In this paper the recent progress in
synthesis of 122-like iron-selenide systems and in experimental research of
their properties is reviewed. Available theoretical data on electronic,
magnetic, and elastic properties of this newest group of superconducting
materials are also discussed.
