Microwave dielectric properties of Na+ and M3+-doped Ba(Mg0.5W0.5)O3 ceramics

In this study, phase evolution, microstructure, and microwave dielectric properties of (Ba0.98Na0.02)(Mg0.48M3+0.02W0.5)O3 (M3+ = Al, Ga, Sc, In, Yb, Y, Dy, Gd, and Sm) ceramics sintered at 1700 °C for 1 h were investigated. All the compounds exhibited an ordered cubic perovskite structure. Regardless of the ionic radius of the doped M3+ ions, BaWO4 was detected as the secondary phase in all the compounds. The field emission scanning electron microscopy (FE-SEM) images revealed a dense microstructure in all the compounds, except in the Al-doped compound, which exhibited an insufficient grain growth. The large and irregularly shaped grains indicated that the liquid phase sintering occurred. Splitting of the A1g(O) mode was observed in the Raman spectra of large M3+ ion-doped compounds. Splitting of the F2g modes did not occur and the bands were sharp, indicating that the cubic symmetry was retained. As the ionic radius of the doped M3+ ions increased, the dielectric constant (εr) increased slightly. The compounds doped with M3+ = Sc, In, Yb, and Y exhibited a very high quality factor (Q × f0) in the range of 250,000 ~ 280,000 GHz. In the case of the compounds doped with M3+ = Al, Ga, Sc, In, Yb, Y, and Dy, the value of the temperature coefficient of resonant frequency (τf) was in the range of −24 ~ −19 ppm/°C, while the Gd and Sm-doped compounds exhibited positive values of 2.8 and 31.2 ppm/°C, respectively. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of the In-doped compound, i.e., (Ba0.98Na0.02)(Mg0.48In0.02W0.5)O3, were 18.7, 286,557 GHz, and − 24.4 ppm/°C, respectively.