Abstract: With the increasing frequency of wireless mobile communication, dielectric materials with higher Q × f are required to enhance the signal strength of microwave passive devices and thus compensate for the rapid attenuation of high-frequency signals during propagation. In order to improve the Q × f of the MgNb₂O₆ system and study the internal mechanism between the structure and microwave dielectric properties, Ta⁵⁺ ion is introduced to design and fabricate MgNb_2-xTa_xO₆ (0 ≤ x ≤ 0.8) ceramics by the solid-state reaction method. The single columbite phase and dense structure are observed throughout the entire composition range. All elements (Mg, Nb, Ta, and O) can be detected by X-ray photoelectron spectroscopy. Insights from the Raman spectroscopy and group theoretical analysis reveal that the A_g(2) and A_g(3) modes located at ∼ 905 cm^-1 dominate the Raman vibration. In addition, the ɛ_r depends on the polarizability reflected by the C-M equation and Raman shift. The τ_f closely relates to the bond energy of the Nb/Ta-O bond and restoring force characterized by average octahedral distortion of [Nb/TaO₆]. Notably, the crucial factors for the huge improvement of Q × f are clarified deeply, in terms of the lower internal strain, the reduced ordering-induced domain size, and the chemical bond valence closer to the ionic valence state, which promotes the stability of crystal structure. Moreover, the introduction of lower electronegative ions enhances the ability of electrons to compensate for oxygen vacancies, thereby reducing the dielectric loss caused by the conductance. Excellent microwave properties (ɛ_r = 19.2, Q × f = 170,000 GHz, and τ_f = -55.6 ppm °C^-1) are achieved in MgNb_1.4Ta_0.6O₆ ceramic, specifically a nearly 40% increase in the Q × f. This work has enriched the theory associated with low dielectric loss and provided the MgNb_1.4Ta_0.6O₆ ceramic with a pretty high-Q × f for the application in the design of the 5G/6G wireless communication devices.

Key words: Advances in 5G/6G materials, High-Q ×f value ceramic, Group theoretical analysis, Oxygen vacancy, Chemical bond characteristics, Microwave dielectric properties