The stable structures of iron pnictides AFeAs (A = alkali and alkaline-earth metals): A first principles study

We have investigated the structural stabilities of iron arsenide compounds Ax(FeAs)1−x (A = alkali and alkaline-earth metals) by first principles calculations. We find that (i) all of the experimental “122” type structures with composition x = 1 / 3 are stable; (ii) all of the “111” type structures with composition x = 1 / 2 except CsFeAs are stable; (iii) K3FeAs with composition x = 3 / 4 is stable. The predicted stable KFeAs, RbFeAs, SrFeAs, BaFeAs, K3FeAs have the As–Fe–As bond angles close to the ideal tetrahedral angles, indicating that they may be superconductors.