Ab initio calculation of the band structure and properties of modifications of the Ti-=SUB=-3-=/SUB=-Sb compound doped with lithium

Abstract

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2x2x2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a=5.217 Angstrem) and tetragonal system (D8m type structure; a=10.457 Angstrem, c=5.258 Angstrem). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8m Ti3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti-Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8m) of Ti3Sb near the Fermi level for s-, p-, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8m) increase the magnetic moment (M) as compared to the value of M (M=0.08 μB) of a "pure" Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb-Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb-Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti-Sb-Li system has been established. The isothermal section of the Ti-Sb-Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (≤6.25 at.% Li) into the Ti3Sb (Space group Pm3 n; N 223; a=5.217 Angstrem) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb-Li supercell. Keywords: Ti3Sb intermetallic compounds, A15 cubic modification, D8m tetragonal modification, doping with lithium, Ti3Sb-Li, DFT-LSDA calculations, supercell, electronic and magnetic properties, Ti-Sb-Li phase stability.