Comparative studies of the electronic structure of LiFePO4, FePO4, Li3PO4, LiMnPO4, LiCoPO4, and LiNiPO4

Abstract

We report a comparative study of the electronic structures of ${\mathrm{LiFePO}}_4,$ ${\mathrm{FePO}}_4,$ ${\mathrm{Li}}_3{\mathrm{PO}}_4,$ ${\mathrm{LiMnPO}}_4,$ ${\mathrm{LiCoPO}}_4,$ and ${\mathrm{LiNiPO}}_4.$ We used the spin-polarized ab initio orthogonalized linear combinations of atomic orbitals method for the calculation. ${\mathrm{Li}}_3{\mathrm{PO}}_4$ is a large-band gap insulator with a band gap of 5.75 eV. For other crystals containing the $\text{3d}$ -transition metals (TM), the localized 3d bands of the TM fall within the large insulting gap. In the cases of ${\mathrm{FePO}}_4$ and ${\mathrm{LiMnPO}}_4,$ the band gaps between the occupied majority spin band and the unoccupied minority spin band are of the order of 0.27 and 1.91 eV, respectively. For ${\mathrm{LiFePO}}_4$ and ${\mathrm{LiCoPO}}_4,$ our calculation shows that they are 100% spin-polarized half metals. In the case of ${\mathrm{LiNiPO}}_4,$ the Fermi level is in the small gap separating $t_{\text{2g}}$ and $e_g$ minority bands. These results are discussed in the context of the number of $\text{3d}$ electrons in the TM series and the possibility of strong electron correlation effects in these crystals.