A Comparative Ab Initio Thermodynamic Study of Oxygen Vacancies in ZnO and SrTiO₃: Emphasis on Phonon Contribution

Abstract

Using a hybrid Hartree–Fock (HF)-DFT method combined with LCAO basis set and periodic supercell approach, the atomic, electronic structure and phonon properties of oxygen vacancies in ZnO and SrTiO3 were calculated and compared. The important role of a ghost basis function centered at the vacant site and defect spin state for SrTiO3 is discussed. It is shown that the use of hybrid functionals is vital for correct reproduction of defects basic properties. The Gibbs free energy of formation of oxygen vacancies and their considerable temperature dependence has been compared for the two oxides. These calculations were based on the polarizability model for the soft mode temperature behavior in SrTiO3. The supercell size effects in the Gibbs free energy of formation of oxygen vacancies in the two oxides are discussed. The major factors for the quite different behavior of the two oxides and the degree of electron delocalization nearby the oxygen vacancy have been identified.

Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals

“…this tetrahedral coordination is characteristic for covalent bonding between sp 3 -hybridized atoms and our results are in good agreement with previous theoretical [81][82][83][84] and experimental data.…”

Phonon spectra of elpasolites Cs2NaRF6 (R=Y,Yb): Ab initio calculations

“…The calculated lattice parameters are compared with the previous experimental results in Table 1. The quality of the calculation of the phonon spectrum cannot be achieved without adequate reproduction of the band structure and the band gap [22]. The results of bandgap value calculations (Table 2) are in good agreement with the experimental data [23].…”

“…Recently calculations for Cs 2 NaYF 6 have been made by means of GGA and LDA approximations with the basis of plane waves [6]. It is important to carry out calculations for homologous crystals of Cs 2 NaRF 6 using hybrid DFT functionals which are well reproducing width of the band gap [7]. In this work the following stages were consistently executed: the optimization of crystal structure, the calculation of a phonon spectrum and elastic constants of Cs 2 NaRF 6 (R=Y, Yb).…”

Cation ordering and oxygen transport behaviour in Sr1−3x/2LaxTiO3perovskites

“…DFT simulations of phonon scattering caused by O vacancies seem to indicate that this might not be the case [30], and this effect would need to be taken into account to produce more accurate defects concentrations.…”