Microwave dielectric properties of (Ba_1-αSr_α)_4.8 (Sm_0.7La_0.3)_8.8 Ti₁₈O₅₄ ceramics

Ba_1-αSr_α)_4.8 (Sm_0.7La_0.3)_8.8 Ti₁₈O₅₄ ceramics were prepared by the solid state reaction. The phase compositions and microstructure were characterized. The microwave dielectric properties were also measured. A single solid solution with new tungsten bronze structure was observed in Ba_1-αSr_α)_4.8 (Sm_0.7La_0.3)_8.8 Ti₁₈O₅₄ ceramics when α=0.3. A secondary phase of BaLa₂Ti₄O₁₂ and La_0.66TiO_2.993 appears subsequently when α>0.3. The relative dielectric constant (ε_r) increased first, and subsequently shows a fluctuating curve with increasing α value. For the quality factor (Q_f), the value of α first increases and then decreases. The α value exhibits a negative effect on the temperature coefficient of the resonance frequency (τ_f). The optimal dielectric properties are achieved in Ba_1-αSr_α)_4.8 (Sm_0.7La_0.3)_8.8 Ti₁₈O₅₄ (α=0.3) ceramic with an ε_r value of 98.77, Q_f of 5184 GHz and τ_f of 10.9 × 10^-6/°C, which is better than the case of BaO-Sm₂O₃-TiO₂ ceramic.