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 x f value of CoNb2O6 system, Ta5+ was introduced into CoNb2O6, and CoNb2-xTaxO6 (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 Ag(2) and Ag(3) modes are the dominant Raman vibrations at approximate to 873 cm-1. Furthermore, the polarization rate affects the epsilon 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 (tau f). The internal strain, ordered induced size, and chemical bonding valence of ionic valence states are the key factors that can increase the Q x 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 CoNb1.8Ta0.2O6 (epsilon r = 21.4832, Q x f = 100723 GHz, tau f = -61.38 ppm/degrees C) ceramics with superior microwave dielectric properties are expected to be used in wireless communication devices.