Synthesis and effect of Ba2+ ions on the dielectric properties of the layered-perovskite KSr2NaNb4O13 ceramics

Abstract

The 25 mol% K2O-added K(Sr2Na)Nb4O13 ceramic sintered at 1275 degrees C exhibited a pure and dense K(Sr2Na)Nb4O13 phase, which had four octahedral layers. Synthesis of a pure K(Sr2Na)Nb4O13 ceramic was not possible without excess K2O, due to the formation of a Na-deficient K(Sr2Na2)Nb5O16 secondary phase, because of K2O evaporation during sintering. The dielectric constant (epsilon(r)) of the K(Sr2Na)Nb4O13 ceramic was 43.8 at 100 kHz, two times higher compared to the KSr2Nb3O10 ceramic, which has three octahedral layers. The increased epsilon(r) can be explained by the increased number of octahedral layers. Some of the Sr2+ ions in K(Sr2Na)Nb4O13 ceramic were replaced by Ba2+ ions, which have high ionic polarizability, to further increase epsilon(r). The 25 mol% K2O-excess K(Sr0.8Ba0.2)(2)NaNb4O13 ceramic sintered at 1250 degrees C showed a high epsilon(r) of 67.4 at 100 kHz, which can be explained by the increased dipole moments and distortion of the NbO6 octahedra.