Superconductivity in ternary iron pnictides: AFe2As2 (A = alkali metal) and LiFeAs

Superconductivity is observed in AFe(2)As(2) (A = Cs, Rb, K) at temperatures below 4 K. The metastable compound NaFe2As2 displays superconductivity with a high T-c = 25 K. These compounds are considered to be strongly hole-overdoped. The stoichiometric LiFeAs is superconducting below 18K. The origin of superconductivity in LiFeAs is critically investigated and we show that Li deficiency cannot explain the experimental results. We propose that superconducting LiFeAs is stoichiometric and it is equivalent to the high-pressure state of other undoped iron pnictides. (C) 2009 Elsevier B.V. All rights reserved.