Complex (Mg1/3Ta2/3)4+ ionic substitution on the phase structure and microwave dielectric properties of wolframite MgZr1−x(Mg1/3Ta2/3)xNb2O8 (0 ≤ x ≤ 0.08) ceramics

In this study, single-phase MgZr_1−x(Mg_1/3Ta_2/3)_xNb₂O₈ (0 ≤ x ≤ 0.08) ceramics with monoclinic wolframite structure were synthesized by the traditional solid-state method. The influences of (Mg_1/3Ta_2/3)⁴⁺ substitution for Zr⁴⁺ on phase composition, microstructure, packing fractions, bond valences, and the microwave dielectric properties of the ceramics were systematically investigated. According to the Rietveld refinement results, with the doping of (Mg_1/3Ta_2/3)⁴⁺, the decline of unit cell volume led to the shift of the main peak in XRD pattern to a higher angle. Furthermore, the trend of the experimental dielectric constant kept in line with the theoretical dielectric constant calculated by the Shannon complex polarizability theory. With the introduction of (Mg_1/3Ta_2/3)⁴⁺ ion, the Q × f values were greatly improved due to the increase of the packing fractions, but the porosity caused by excessive substitution deteriorates the quality factor. The increase of B-site bond valence explained the decline of τ_f. In particular, the MgZr_1−x(Mg_1/3Ta_2/3)_xNb₂O₈ (x = 0.04) ceramics sintered at 1340 °C for 4 h exhibited optimal microwave dielectric properties of ε_r = 25.42, Q × f = 65,950 GHz, and τ_f =  − 61.04 ppm/°C.