First-principles and semiempirical Hartree-Fock calculations for F centers in KNbO[sub 3] and Li impurities in KTaO[sub 3]

Abstract

Abstract. The linear muffin-tin-orbital method based on the density-functional theory and the semi-empirical method of the Intermediate Neglect of the Differential Overlap based on the Hartree-Fock formalism are used for the supercell study of the F centers in cubic and orthorhombic ferroelectric KNbO 3 crystals. Two electrons are found to be considerably delocalized even in the ground state of the defect. The absorption energies were calculated by means of the INDO method using the ∆SCF scheme after a relaxation of atoms surrounding the F center.As an example of another type of point defect in perovskite, an isolated Li impurity in KTaO 3 as well as interacting Li pairs are considered in the supercell approach, using the supercells of up to 270 atoms. The off-center Li displacement, reorientational energy barriers and the lattice relaxation around impurities are calculated. The results are compared with those obtained earlier within the shell model, revealing the relaxation pattern somehow different from the shell model estimations.

Strain‐mediated electrical and optical properties of novel lead‐free CuFe2O4–KNbO3 nanocomposite solid solutions: A combined experimental and Density Functional Theory studies

“…The band structures shown in Figure 11 of KNbO 3 agree with the other DFT works (Eglitis et al, 1997; Azam et al, 2019). The bandgap is indirect along the Γ–M direction and the bandgap of KNbO 3 in CK1, CK2, and CK3 samples are found to be 2.744, 2.798, and 2.72 eV, respectively.…”