Structure evolution of wolframite-type ZnZrC2O8 (C = Nb, Ta) ceramics in relation to microwave dielectric properties

The relationship among the sintering behavior, crystal structure, chemical bonding properties, and dielectric properties of wolframite-type ZnZr(Nb1-xTax)(2)O-8 (0.0 <= x <= 1.0) ceramics was investigated with the progressive replacement of Nb5+ by Ta5+. The optimum sintering temperature increases from 1225 to 1375 degrees C with increasing Ta5+ content. The epsilon(r) value falls from 27.34 to 22.34 due to a gradual decrease in bond ionicity and a shift in the Raman vibration modes toward higher wave numbers. The Q x f increases from 63 604 GHz (@6.71 GHz) to 115 631 GHz (@7.89 GHz), which is since the increase in the total lattice of chemical bonds. Moreover, the reduction in grain boundary area and the gradual lowering of the full width at half maximum of the Raman vibration modes contribute to the reduction in dielectric losses. First-principles calculations illustrate that the growth in bandgap and electron cloud density in the internal space of the [Zn/ZrO6] octahedron leads to a reduction in dielectric loss. Furthermore, the reduced degree of oxygen octahedral distortion causes a change in tau(f) from -46.56 to -37.40 ppm/degrees C.