Elastic properties and inter-atomic bonding in new superconductor from first principles calculations

Very recently [J. Guo, S. Jin, G. Wang, S. Wang, K. Zhu, T. Zhou, M. He, X. Chen, Phys. Rev. B 82 (2010) 180520R. arXiv:1012.2924.] the first 122-like ternary superconductor KxFe2Se2 with enhanced T C ∼ 31 K was discovered. This finding has stimulated much activity in search of related materials and triggered the intense studies of their properties. Indeed already in 2010–2011 the superconductivity ( T C ∼ 27 – 33 K ) was also found in the series of new synthesized 122 phases such as CsxFe2Se2, RbxFe2Se2, (TlK)xFeySe2etc. which have formed today the new family of superconducting iron-based materials without toxic As. Here, using the ab initio FLAPW-GGA method we have predicted for the first time the elastic properties for KFe2Se2 and discussed their interplay with inter-atomic bonding for this system. Our data reveal that the examined phase is a relatively soft material. In addition, this system is mechanically stable, adopts considerable elastic anisotropy, and demonstrates brittleness. These conclusions agree with the bonding picture for KFe2Se2, where the inter-atomic bonding is highly anisotropic and includes ionic, covalent and metallic contributions.