Structural stability and electronic properties of the new superconductor (Ca4Al2O6 − x )(Fe2As2) from first-principles study
Authors: Zhang, Yun-Li; Zhang, Ji-Hua; Tao, Xiang-Ming; Tan, Ming-Qiu
Source: Superconductor Science and Technology, Volume 24, Number 10, October 2011 , pp. 105014-105020(7)
Publisher: IOP Publishing
Abstract:Density-functional theory calculations are performed on (Ca4Al2O6 − x )(Fe2As2) to address the structural stability and electronic properties. The total-energy calculations show that the ground state of the parent compound (Ca4Al2O6)(Fe2As2) has striped anti-ferromagnetic order with anti-ferromagnetic coupling between Fe layers. The oxygen vacancy formation energy at the 4f site (~6.02 eV) is smaller than that at the 2c site (~6.33 eV) for the (Ca4Al2O6 − x )(Fe2As2) (x = 1) phase, which means oxygen vacancies can be easily formed at the 4f site. Further studies show that the ground state of (Ca4Al2O6 − x )(Fe2As2) (x = 0.25) is identical to the case of (Ca4Al2O6)(Fe2As2), which implies that the spin density wave (SDW) may coexist with superconductivity in the (Ca4Al2O5.75)(Fe2As2) phase. The densities of states (DOSs) of (Ca4Al2O6 − x )(Fe2As2) (x = 0, 0.25) show that both spin-up and spin-down DOSs at the Fermi energy level become larger obviously due to oxygen vacancies being introduced, which means introducing oxygen vacancies in (Ca4Al2O6)(Fe2As2) is beneficial for improving its conductivity. These results will be helpful for synthesizing new 42 622-type structured iron-based superconductors with oxygen vacancies.
Document Type: Research Article
Publication date: October 1, 2011