Preparation and characterization of K-substituted NaCa₄Nb₅O₁₇ microwave dielectric ceramics

Abstract

The effect of K substitution for Na on the phase, microstructure and microwave dielectric properties of the Na_1−x K _x Ca₄Nb₅O₁₇ (x = 0–1) composition series was investigated. The compositions with x = 0, 0.5 and 1 formed single-phase Na_1−x K _x Ca₄Nb₅O₁₇ ceramics within the detection limit of the in-house XRD facility when sintered at 1,200–1,300 °C. At x = 0.25 and 0.75, the major Na_1−x K _x Ca₄Nb₅O₁₇ phase formed but along with a secondary CaNb₂O₆ phase. Relative permittivity (ε _r ) and temperature coefficient of resonant frequency (τ_f) increased from 45 to 51 and −120 to +473 ppm/ °C respectively while the quality factor (Q × f _o ) decreased from 13,838 to 2,374 GHz with an increase in x from 0 to 1. Optimum microwave dielectric properties (i.e. ε _r  = 47, Q × f _o  = 5,047 GHz and τ_f = − 23 ppm/ °C) were achieved for the x = 0.5 (i.e. Na_0.5K_0.5Ca₄Nb₅O₁₇) composition. Further investigations are required to improve the density and hence microwave dielectric properties of Na_1−x K _x Ca₄Nb₅O₁₇ ceramics.