Effects of ZrO2 substitution on crystal structure and microwave dielectric properties of Zn0.15Nb0.3(Ti1-xZrx)0.55O2 ceramics

In this study, the influence of substitution of Zr for Ti on crystal structure and microwave dielectric properties of Zn_0.15Nb_0.3(Ti_1-xZr_x)_0.55O₂ (0 ≤ x ≤ 0.7) ceramics were discussed through Rietveld refinement, normalized bond analysis and complex chemical bond theory. Rietveld refinement analysis indicated that a composite could be formed for x ≤ 0.22. Pure orthorhombic type (O-type) solid solutions are prepared in the region of x = 0.3–0.7. With the increasing amount of ZrO₂, cell volume of O-type phase increases, and it results in the enlarging and compressing behaviors of chemical bonds. Under the circumstances, the dielectric polarizability is deteriorated because of the reducing chemical bond covalency value (f_c), and this finding is also confirmed by Clausius-Mosotti equation. Lattice energy of Zr–O1 bonds and grain size distribution of sintered specimens are mainly responsible for the variations of quality factor (Q × f) value. Chemical bond energy (E) is closely related with the temperature coefficient of resonant frequency value (τ_f). Typical microwave dielectric properties of Zn_0.15Nb_0.3(Ti_1-xZr_x)_0.55O₂ ceramics (x = 0.22) were obtained when sintered at 1100 °C: ε_r = 46.31, Q × f = 30,297 GHz, τ_f = -8.24 ppm/°C.