Stability, structural, elastic, and electronic properties of polymorphs of the superconducting disilicide YIr 2Si 2

Abstract

Using the ab initio approaches, the comparative stability, structural, elastic, and electronic properties of three polymorphs of the superconducting disilicide YIr 2Si 2, which differ in the atomic configurations of [Ir 2Si 2] (or [Si 2Ir 2]) blocks, were examined. For these YIr 2Si 2 polymorphs, the optimized structural data, elastic parameters, electronic bands, total and partial densities of states, Fermi surface topology, and chemical bonding were obtained and analyzed. Our studies showed that although ThCr 2Si 2- and CaBe 2Ge 2-type polymorphs are mechanically stable and relatively hard materials with low compressibility, they will behave as ductile systems. Among them, ThCr 2Si 2-type polymorph will show enhanced elastic anisotropy. In the vicinity of the Fermi energy, the topology of the electronic bands and the Fermi surface for various polymorphs are quite different. Besides, the CaBe 2Ge 2-type polymorph is expected to be anisotropic, i.e. happening mainly in the [Si 2Ir 2] blocks. The inter-atomic bonding for YIr 2Si 2 polymorph phases can be described as an anisotropic mixture of covalent, metallic, and ionic contributions, where inside the [Ir 2Si 2] (or [Si 2Ir 2]) blocks, Ir–Si and Ir–Ir bonds take place, whereas between the adjacent [Ir 2Si 2] (or [Si 2Ir 2]) blocks and Y atomic sheets, Si–Si and Ir–Y, Si–Ir and Si–Y, or mainly Ir–Ir bonds emerge for various polymorphs.