Local dynamics and structure of pure and Ta substituted ( K<inf>1-x</inf> Na<inf>x</inf> ) NbO<inf>3</inf> from first principles calculations

Abstract

The local structure and dynamics of piezoelectric K1-x Na xNbO3 perovskite solid solutions with and without partial Ta substitution at x=0.5 are investigated using first principles calculations for supercells. The results are analyzed locally using the dynamical pair distribution functions. The local structures for Ta-substituted material show smaller off-centering of Ta compared to Nb. In addition, the dynamics of the relaxed structure indicate softer Nb force constants relative to Ta even though the Nb has shorter O nearest-neighbor distances than Ta. These results are discussed in relation to experimental measurements which show a decrease in Curie temperature and an increase in dielectric constant when Ta is partially substituted into K1-x NaxNbO3. © 2010 The American Physical Society.