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

The 25 mol% K₂O-added K(Sr₂Na)Nb₄O₁₃ ceramic sintered at 1275 °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 (ε_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 ε_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 ε_r. The 25 mol% K₂O-excess K(Sr_0.8Ba_0.2)₂NaNb₄O₁₃ ceramic sintered at 1250 °C showed a high ε_r of 67.4 at 100 kHz, which can be explained by the increased dipole moments and distortion of the NbO₆ octahedra.