Ta doping effect on microstructure and microwave dielectric properties of CoNb2O6-based ceramics and mechanism study

As communication technology continues to evolve, 5G technology is becoming more mature, and 6G technology is steadily advancing. Microwave equipment is moving toward high frequency, miniaturization, low loss and high temperature stability, and microwave dielectric ceramics have been deeply applied in this field. To elevate the Q × f value of CoNb₂O₆ system, Ta⁵⁺ was introduced into CoNb₂O₆, and CoNb_2-xTa_xO₆ (0.0 ≤ x ≤ 0.8) ceramics were prepared by the traditional solid-phase method. By X-ray diffraction, it was observed that at x = 0.8, in addition to a single niobium ferrite phase, information of tantalate phase also appeared. Raman spectral detection and group theory analysis indicate that A_g(2) and A_g(3) modes are the dominant Raman vibrations at ≈873 cm⁻¹. Furthermore, the polarization rate affects the ε_r value, and the bond energy of Nb/Ta-O and the recovery force characterized by the average deformation of the [Nb/TaO₆] octahedron are the key elements influencing the temperature coefficient of the resonance frequency (τ_f). The internal strain, ordered induced size, and chemical bonding valence of ionic valence states are the key factors that can increase the Q × f value. Moreover, the introduction of ions with lower electronegativity leads to an enhanced electronic compensation of oxygen vacancies, which also reduces the dielectric loss. This paper enriches the theory related to low dielectric loss and shows that CoNb_1.8Ta_0.2O₆ (ε_r = 21.4832, Q × f = 100723 GHz, τ_f = -61.38 ppm/°C) ceramics with superior microwave dielectric properties are expected to be used in wireless communication devices.