Ultra-high Quality Factor of (Zn_2/3Nb_1/3)³⁺ Co-substitution MgAl₂O₄ Microwave Dielectric Ceramics

Herein, nominal compositions of MgAl2-x(Zn2/3Nb1/3)(x)O-4 (x = 0.00, 0.04, 0.08, 0.12, 0.16, 0.20, 0.30, 0.40, and 0.50) ceramics are synthesized using a solid-phase reaction method. The (Mg/Zn)Al2O4 solid solution and second-phase Mg4Nb2O9 greatly improve the microwave dielectric properties of the samples. Moreover, the second phase, ionic polarizability, and relative density affect the dielectric constant (epsilon(r)) value. The quality factor (Qf) value is correlated with the packing fraction, achieving a maximum value of approximate to 563 000 GHz at x = 0.40. The temperature coefficient of the resonant frequency (tau(f)) value is negatively correlated with the B-site bond value. When x = 0.40, the nominal composition MgAl1.6(Zn2/3Nb1/3)(0.4)O-4 ceramic exhibits good microwave dielectric properties: epsilon(r) = 9.06, ultrahigh Qf = 563 000 GHz, and tau(f) = -45 ppm degrees C-1.