Elastic properties and inter‐atomic bonding in layered Fe–Cu arsenide oxide Sr₂Fe₂CuAs₂O₂

Abstract

Inspired by recent discovery of the layered five-component phase -the tetragonal arsenide oxide Sr 2 Fe 2 CuAs 2 O 2 uniting two types of [Fe 2 As 2 ] and [CuO 2 ] blocks, which are the main building blocks inherent in two basic families of high-T C superconductors: so-called cuprates and iron-pnictides, we used the first principles calculations to predict the elastic properties and to find their interplay with inter-atomic bonding for this unique system. Our data reveal that the examined phase is a relatively soft material; the predicted bulk and shear modules are about 90 and 54 GPa, respectively. Besides, this system is mechanically stable, adopts considerable elastic anisotropy, and should demonstrate brittleness. These conclusions agree with the bonding picture for Sr 2 Fe 2 CuAs 2 O 2 , according to which the inter-atomic bonding in this system is highly anisotropic and includes ionic, covalent, and metallic contributions, where inside [Fe 2 As 2 ] and [CuO 2 ] blocks covalent-ionic Fe-As, Cu-O and metallic-like Fe-Fe bonds take place, whereas inter-blocks bonding is basically of the ionic type.