Vibrational studies and microwave dielectric properties of a-site-substituted tellurium-based double perovskites

A(2)MgTeO(6) (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: epsilon(r) of 11, 14.3, and 13.2; Q(u)xf of 25, 27.5, and 81 THz, and tau(f) of -16, -61, and -81 ppm/degrees 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 14/m space group, while Ca-based materials exhibit a monoclinic P2(1)/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.