Effects of Ca2+ substitution on microstructure and microwave dielectric properties of low loss Ba(Mg1/3Nb2/3)O3 perovskite ceramics.

Ba_1−xCa_x(Mg_1/3Nb_2/3)O₃ (0 ≤ x ≤ 0.02) perovskite ceramics were prepared by the solid-state reaction method. The phase composition and microstructure were characterized by XRD and SEM, respectively. The result showed that all ceramics exhibited the 1:2 ordered perovskite structure, and the grain size decreased first and then increased with different substitution amount of Ca²⁺ for Ba²⁺. The dielectric properties were examined by Vector network analyzer, and the Raman spectra was used to interpret the dielectric properties of Ba_1−xCa_x(Mg_1/3Nb_2/3)O₃ ceramics. The dielectric constant (ε_r) were strongly depended on the Raman shift of A_1g(O) stretch mode, and the quality factor (Q × f) manifested great correlated with the full width at half maxima (FWHM) of A_1g(O) stretch mode. The Ba_1−xCa_x(Mg_1/3Nb_2/3)O₃ ceramics substituted of Ca²⁺ for Ba²⁺ in x = 0.005, which possessed the narrowest FWHM and the highest degree of 1:2 ordering, showed the best microwave dielectric properties: ε_r = 31.64, Q × f = 74421 GHz, τ_f = 14.59 ppm/°C. [ABSTRACT FROM AUTHOR]