Crystal structure and microwave dielectric properties of Mg²⁺-Si⁴⁺ co-modified yttrium aluminum garnet ceramics

In this article, garnet-type Y₃Al₅O₁₂ (YAG) were doped with Mg²⁺-Si⁴⁺ ionic pairs and its effect on the structure and the microwave dielectric properties was investigated. It was revealed that in ceramics Y₃Mg_xAl_5-2xSi_xO₁₂ (x = 0, 0.5, 1.0, 1.5, 2.0), increasing doping concentration decreased the sintering temperature and time for the optimal densification. X-ray diffraction studies showed that the samples are isostructural to Al₅Y₃O₁₂ garnet. All sample were formed a single phase except for x = 2.0, where a secondary peak was detected. Excellent microwave dielectric properties of ε_r = 10.56, Q × f = 67,571 GHz and τ_f = -35.23 ppm/°C were obtained for Y₃Mg_0.5Al₄Si_0.5O₁₂ ceramics sintered at 1625 °C for 5 h. The factors influencing the microwave dielectric properties of Y₃Mg_xAl_5-2xSi_xO₁₂ ceramics were further discussed by considering the ionic polarization, packing fraction, average grain size and chemical bond valence theory.