Microwave and terahertz dielectric properties of CoNb _1.8 Ta _0.2 O ₆ ‒TiO ₂ ceramic systems

Abstract In this paper, (1 ‒ x )CoNb 1.8 Ta 0.2 O 6 ‒ x wt.% TiO 2 (0 ≤ x ≤ 20) system ceramics were prepared by the conventional solid‐phase method, and the process of the phase change of the ceramics in this system was systematically discussed by X‐ray diffraction and Raman spectroscopy: niobiumite‒niobiumite + rutile‒rutile. The process of the phase change generated by TiO 2 doping is accompanied by an increase in the size of the grains, and the crystal cell volume reduction and changes in packing fraction, etc. The microwave dielectric properties changed with the doping of TiO 2 . Excellent microwave dielectric properties were obtained by sintering the ceramics at x = 5 wt.% for 6 h at 1250°C: ε r = 25.36 ± 0.5, Q × f = 17 093 ± 500 GHz, and τ f = 0 ± 4 ppm/°C. In addition, combined with terahertz time‐domain spectroscopy techniques, the terahertz dielectric properties were tested. The effects of lattice distortion, packing fraction, and electronic and ionic polarization on the terahertz dielectric properties were analyzed in analogy with the dielectric properties in the microwave band.