Dielectric properties of Ln2O3-WO3 ceramics at microwave frequencies

A series of Ln2WO6 (Ln = La, Nd, Sm, Eu, and Gd) ceramics were prepared through the solid state reaction route. The effects of rare-earth elements at Ln-site on the phase purity, crystal structure, and microwave dielectric properties were analyzed by XRD, Rietveld refinement, SEM and dielectric measurements. The nominal La2WO6 and Nd2WO6 would not form a single phase but exhibited mixed phases, whereas the Sm2WO6, Eu2WO6, and Gd2WO6 ceramics crystallized in a pure monoclinic crystal structure. The optimized microwave dielectric properties were obtained with εr = 18.75, Q×f = 4350 GHz and τf = −41.0 ppm/°C for Sm2WO6, εr = 18.43, Q×f = 19,500 GHz, τf = −44.1 ppm/°C for Eu2WO6, and εr = 17.50, Q×f = 4400 GHz, τf = −10.3 ppm/°C for Gd2WO6 sintered 1520 °C. The relationship between the composition and microwave dielectric properties were studied with respect to the ionic polarization and packing fraction.