Ordered domain structure and octahedral tilting in Ba ₁₋ <i> _x </i> Sr <i> _x </i> (Mg _1/3 Nb _2/3 )O ₃ microwave dielectric ceramics

Abstract The B ‐site ordered Ba‐based complex perovskites represent a significant class of medium permittivity and low‐loss microwave dielectric ceramics, demonstrating extensive applications in microwave communication fields. Single‐phase Ba 1− x Sr x (Mg 1/3 Nb 2/3 )O 3 ( x = 0 ∼ 1) ceramics were designed and synthesized using the standard solid‐state sintering method to evaluate the co‐effects of ordered domain structure and octahedral tilting on microwave dielectric properties in complex perovskites. A comprehensive investigation was conducted to elucidate the composition‐dependent evolution of crystal structures, ordered domain structures, and octahedra tilting. B ‐site 1:2 ordering was observed in all the compositions, while the highest ordering degree S = 0.98 and maximum Qf value of 47 400 GHz were achieved in Ba 0.75 Sr 0.25 (Mg 1/3 Nb 2/3 )O 3 . With increasing Sr, the crystal structure transforms from a triangle P 3 ̅ m 1 phase to a space group of P2 1 /c with both antiphase and in‐phase tilting, while a near‐zero τ f of −7.8 ppm/°C was obtained at x = 0.7. The variation of τ f followed the empirical law well with the tolerance factor. Moreover, by annealing at 1350°C for 12 h, τ f shifted closer to zero ( τ f = −3 ppm/°C) with improved Qf value, stable ε r , and increased S value in ceramics with x = 0.7. This systematic study revealed the underlying mechanisms governing the influence of these structural parameters on the microwave dielectric performance, and provided useful guidance for collaborative optimization of microwave dielectric properties.