Evaluation of electronic state of Mg4(Nb2−xSbx)O9 microwave dielectric ceramics by first principle calculation method

The microwave dielectric properties of Mg4(Nb2−xSbx)O9 (MNS) solid solutions were evaluated and the variations in the electric state of the solid solutions were also investigated by using the first principle calculation method. The formation of a single phase was observed from the X-ray powder diffraction patterns of the solid solutions sintered at 1400 °C in the composition x from 0 to 1. The MgO and Mg7Sb2O12 compounds were detected as the secondary phases at the compositions higher than x = 1; therefore, this result is closely related to the vaporization of Sb in this composition range. When comparing the overlap population of the (NbMg12O45)−61 cluster model with that of the (SbMg12O45)−61 cluster model, the slight covalency of the SbO bond was recognized from the results of the first principle calculation method. In the composition range of 0–1, the Q·f values of MNS sintered at 1400 °C increased from 196,000 to 280,000 GHz; the dielectric constants of the solid solutions ranged from 13 to 10. However, an improvement in the temperature coefficient of resonant frequency with the Sb substitution for Nb was not recognized.