Relative phase stability and lattice dynamics of NaNbO3from first-principles calculations

Abstract

We report total energy calculations for different crystal structures of NaNbO 3 over a range of unit cell volumes using the all-electron full-potential (L)APW method. We employed both the local-density approximation (LDA) and the Wu-Cohen form of the generalized gradient approximation (GGA-WC) to test the accuracy of these functionals for the description of the complex structural behavior of NaNbO 3 . We found that LDA not only underestimates the equilibrium volume of the system but also predicts an incorrect ground state for this oxide. The GGA-WC functional, on the other hand, significantly improves the equilibrium volume and provides relative phase stability in better agreement with experiments. We then use the GGA-WC functional for the calculation of the phonon dispersion curves of cubic NaNbO 3 to identify the presence of structural instabilities in the whole Brillouin zone. Finally, we report comparative calculations of structural instabilities as a function of volume in NaNbO 3 and KNbO 3 to provide insights for the understanding of the structural behavior of K 1-x Na x NbO 3 solid solutions.2

Suppression of antiferroelectric state in NaNbO3 at high pressure from in situ neutron diffraction

“…Although great effort has been devoted to understand the fundamental mechanism of the phase transitions observed in NaNbO 3 using first principle calculations [21][22][23][24][25], we still have little knowledge due to presence of several competing structural instabilities with very similar free energies. Theoretically, we can predict the transition pressure by plotting the free energy as a function of pressure for various phases and identifying the phases of minimum free energy.…”

Electronic and Optical Properties of Sodium Niobate: A Density Functional Theory Study

“…As has been shown recently for oxide semiconductors, this might improve with a self-consistent determination of the amount of Hartree-Fock exactexchange mixed into the hybrid functional [20]. However, as already mentioned by Machado et al [15], it is not correct to directly compare the high-temperature measurements of the simple cubic perovskite Pm3m phase with the zerotemperature DFT calculations.…”

“…Diéguez et al [13] reported a first-principle study of epitaxial strain in perovskites, including KNbO 3 and NaNbO 3 , while Li et al [14] reported density functional theory (DFT) calculations for epitaxially strained KNbO 3 /NaNbO 3 superlattices, thereby including the unstrained simple cubic perovskite phase (Pm3m) as well. Finally, Machado et al [15] reported on the relative phase stability and lattice dynamics of NaNbO 3 from first principles. A rigorous assessment of the performance of different exchange-correlation functionals within DFT calculations and applied to the possible crystalline phases of NaNbO 3 at room temperature and below is still missing to date.…”

Structural determination and electronic properties of the 4dperovskite SrPdO3

“…53 These instabilities are very common in cubic perovskites and were very well studied. [54][55][56] Having established the phonon instabilities of the ideal cubic phase we now present the outcomes of our structural search, which is based on the stabilization of the negative phonon modes through suitable atomic displacements.…”