Phase composition and microwave dielectric properties of two garnet structured Y2BaM4SiO12 (M = Al, Ga) ceramics with large size Ba cations on A-site

In this work, two novel Ba-contained Y₂BaM₄SiO₁₂ (M = Al, Ga) ceramics with garnet structured were obtained by a solid-state reaction method. XRD patterns combined with Rietveld refinement analysis demonstrated that Y₂BaAl₄SiO₁₂ was formed a single cubic structure phase with an Ia-3d space group. While in the Y₂BaGa₄SiO₁₂ ceramics, apart from the main phase of garnet structure, a trace of peaks of SiO₂ were also detected. The bond valence and P–V–L chemical bond theory analysis results indicated that both of Ba cations presents a strength compressed effect in the Y₂BaM₄SiO₁₂ (M = Al, Ga) ceramics. And the large lattice energy of Al-O bonds might be the main reason for the Y₂BaAl₄SiO₁₂ formation of a stable garnet crystal structure without secondary phase and high Q × f values. The Y₂BaGa₄SiO₁₂ ceramics with a low relative density (91%) and microwave dielectric properties of ε_r = 12.6, Q × f = 4,530 GHz, and τ_f = − 28.6 ppm/°C. The dense Y₂BaAl₄SiO₁₂ ceramics (relative density of 96.2%) with microwave dielectric properties of ε_r = 10.3, Q × f = 8,700 GHz, and τ_f = − 20.3 ppm/°C was obtained at 1360 °C for 4 h. In the garnet structure, all the results demonstrates that the mismatch among the A-sites or C-sites cations will result in a low-fired temperature and severely deteriorated Q × f values.