First-principles prediction of superconductivity in LiBSi1-xAlx

Abstract

Electronic structure, lattice dynamics and superconducting properties for theoretically devised superconductor LiBSi 1-x Al x are obtained by first-principles calculations. We assume that Lithium Boron Silicon ( LiBSi ) has the same crystal structure as that of Lithium borocarbide ( LiBC ). The pristine LiBSi is predicted to be a zero-gap semiconductor. Hole doping of LiBSi through partial substitution of Si by SiAl atoms can produce a semiconductor–metal transition and develop superconductivity. To assess the thermodynamic stability of LiBSi 1-x Al x, the formation energies are calculated using the supercell method. For LiBSi 0.75 Al 0.25 and LiBSi 0.875 Al 0.125, the obtained formation energies are -5.9 and -6.1 eV, respectively, indicating that LiBSi 1-x Al x is energetically favorable at least in the range of 0 ≤ x ≤ 0.25. Phonon spectra and superconducting properties are obtained within the virtual-crystal approximation (VCA) treatment. The results show that LiBSi 1-x Al x is dynamically stable approximately in the range of 0 ≤ x ≤ 0.35. For LiBSi 0.8 Al 0.2, the obtained electron-phonon coupling constant λ is 0.86 and superconducting transition temperature TC is predicted to be in the range of 11–13 K (0.14 ≥ μ* ≥ 0.1).