Vibrational Studies and Microwave Dielectric Properties of A-Site-Substituted Tellurium-Based Double Perovskites

Abstract

A2MgTeO6 (A = Ba, Sr, Ca) ceramics were prepared by solid-state route and their microstructure and microwave dielectric properties, as well as the vibrational phonon modes were investigated using the resonance method and spectroscopic techniques for the first time. For the optimized sintering temperatures, Ba2MgTeO6, Sr2MgTeO6, Ca2MgTeO6 materials presented the following properties: εr of 11, 14.3, and 13.2; Quxf of 25, 27.5, and 81 THz, and τf of −16, −61, and −81 ppm/°C, respectively. XRD besides Raman and infrared spectroscopies were employed to investigate the structures of these materials and the results showed that Ba- and Sr-based double perovskites belong to the tetragonal I4/m space group, while Ca-based materials exhibit a monoclinic P21/n structure. The phonon modes were evaluated and the intrinsic microwave dielectric properties were discussed in terms of the A-site substitution on tellurium-based ceramics. The number of bands observed in both spectroscopic techniques agrees well with the group-theoretical predictions for all materials, thus confirming our assumptions.