First-principles study of the intrinsic defects in PbFCl

First-principles pseudopotential calculations have been performed to investigate intrinsic defects including vacancies, interstitials, antisite defects, as well as Schottky and Frenkel defects in PbFCl crystals. For the isolated vacancies and interstitials, their formation energies are critically dependent on the atomic chemical potentials and electron Fermi energy. The charged defects for vacancies and interstitials are stable in a wide range of Fermi level, suggesting a strong ionization tendency. The present calculations also reveal that the formation energies of Schottky defects are much lower than those of Frenkel defects. Therefore it can be concluded that the Schottky defects are dominant in PbFCl crystals. Furthermore, Schottky defects (V-Pb+V-F+V-Cl) exhibit the lowest formation energy of 2.21 eV. Defect transition energy levels can occur between different charged states. The anion interstitials and the cation vacancies form acceptorlike defects with transition energies of 1.05, 0.57, and (0.47,0.9) eV for F-i, Cl-i and V-Pb, respectively, while V-F, V-Cl, and Pb-i have high transition energies of more than 3 eV. In addition, the calculated profiles of densities of states for the defective supercells show that some extra states may appear in the band gap.