Relationship between crystal structure and microwave dielectric properties of melilite-type ceramic

Crystal structure–microwave dielectric property relations in the melilite-type Ba2(Mg1−xZnx)Si2O7 ceramics were investigated in this study. The formation of a secondary phase was not detected over the whole composition range. Also, the lattice parameter, a, of the solid solutions decreased linearly with increasing the composition x, while the lattice parameter, c, was increased by the Zn substitution for Mg. Also, the covalency of the MgO bond increased from 26 to 35% in the composition range of 0–0.75. Moreover, the covalency of the ZnO bond increased in the composition range of 0.25–1, while that of SiO bonds in the SiO4 tetrahedron remained approximately constant over the whole composition range. The dielectric constants (ɛr) of the solid solutions were on the order of approximately 7.5, and the quality factors (Q·f) of the solid solutions increased with increasing the composition x. The temperature coefficient of resonant frequency (τf) of the solid solutions varied from −62 to −74 ppm/°C with increasing the composition x; therefore, the Zn substitution for Mg was not effective in improving the τf value in this system.