Structure, microstructure, and microwave dielectric properties of (Sr _2-xCa_x)(MgTe)O₆ double perovskites

Sr_2-xCa_xMgTeO₆ (0 ≤ x ≤ 2) ceramics were prepared by the solid-state ceramic route. Structure and microstructure of the compounds were investigated using XRD, TEM, and SEM methods. The system undergoes a transition from pseudocubic tetragonal I4/m symmetry for x = 0 (Sr₂MgTeO₆) to pseudotetragonal monoclinic P2 ₁/n symmetry for x > 0. The dielectric properties of the ceramics were studied by the resonance method. The temperature coefficient of resonant frequency is negative throughout the series; permittivities were in the range 13.2-14.3, and quality factors varied from 27 500 to 81 000 (5-6 GHz).