Calculation of the structural, energetic, electronic, and magnetic properties of LiAl5O8 doped with Fe and Cr: Ab initio method

Abstract

Ab initio calculations based on density functional theory are used to study the structural, energetic, electronic, and magnetic properties of lithium aluminate (LiAl5O8) spinel doped with Fe and Cr. Two possible schemes are considered: (1) doping with Fe or Cr at the Al3+ 8c site and (2) doping with Fe or Cr at the Al3+ 12d site. Exchange and correlation effects are described via the generalized gradient approximation PBEsol functional (structural properties) and the modified Becke-Johnson potential (defect formation energy, electronic structure, and magnetic properties). For each scheme, the local structure around the defect is predicted. Our calculations show that Fe and Cr prefer the octahedral site of Al. A Bader analysis shows that the defect charge is 3 + for both Fe and Cr. Calculation of the electronic structure shows that the 3d states of Cr3+ and Fe3+ are below the Fermi energy and within the band gap of LiAl5O8. For replacement of Al by Fe, the state density calculation shows that Fe3+ has a valence electron configuration of 4s03d5 (8c and 12d sites). For replacement of Al by Cr, it is found that Cr3+ has a valence electron configuration of 4s03d3 (8c and 12d sites). There is a magnetic moment in the unit cell due to the presence of Cr and Fe in the LiAl5O8 lattice.