Improvement in the microwave dielectric properties of SrCa4Nb4TiO17 ceramics by Ba substitution

Microwave dielectric ceramics in the Sr1−xBaxCa4Nb4TiO17 (0 ≤ x ≤ 0.75) composition series were fabricated via a solid-state mixed oxide route. All the compositions formed single phase in Sr1−xBaxCa4Nb4TiO17 (0 ≤ x ≤ 0.75) solid solutions within the detection limit of in-house X-ray diffraction (XRD). The sintered microstructure of these ceramics comprised densely packed elongated and plate-like grains. The dielectric properties varied linearly with x. Relative permittivity (εr) increased from 47.2 to 54.5, unloaded quality factor multiplying the resonant frequency (Qufo) decreased from 11,984 to 9345 GHz and temperature coefficient of resonant frequency (τf) increased from −78.6 to 20 ppm/°C with an increase in x from 0 to 0.75. In the present study, εr ≈ 51.6, Qufo ≈ 10,160 GHz (5.37 GHz) and τf ≈ −13.5 ppm/°C were achieved for Sr0.5Ba0.5Ca4Nb4TiO17 (x = 0.5) ceramics.