Relative phase stability and lattice dynamics of NaNbO3 from first-principles calculations

MACHADO, RODRIGO; SEPLIARSKY. MARCELO; STACHIOTTI, MARCELO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2011 vol. 84 p. 1341071 - 1341077

0163-1829

We report total-energy calculations for different crystal structures of NaNbO3 over a range of unit-cell volumesusing the all-electron full-potential (linearized) augmented plane-wave method. We employed both the local-density approximation (LDA) and the Wu-Cohen form of the generalized gradient approximation (GGA-WC) totest the accuracy of these functionals for the description of the complex structural behavior of NaNbO3 . We foundthat LDA not only underestimates the equilibrium volume of the system but also predicts an incorrect groundstate for this oxide. The GGA-WC functional, on the other hand, significantly improves the equilibrium volumeand provides relative phase stability in better agreement with experiments. We then use the GGA-WC functionalfor the calculation of the phonon-dispersion curves of cubic NaNbO3 to identify the presence of structuralinstabilities in the whole Brillouin zone. Finally, we report comparative calculations of structural instabilities asa function of volume in NaNbO3 and KNbO3 to provide insights for the understanding of the structural behaviorof K1 Nax NbO3 solid solutions.