Crystal structure,phase transition,vibrational spectra,and microwave dielectric characteristics of Ta5+ ionic substituted Co0.5Ti0.5NbO4 ceramics

In the present research, structural representation, phase transition, and dielectric characteristics of Ta⁵⁺ ionic substituted Co_0.5Ti_0.5(Nb_1-xTa_x)O₄ (x = 0–1) ceramics were thoroughly investigated. Combined with the changes of diffraction peaks in the X-ray diffraction spectra, such as (002) and (101) crystalline planes near 20°, and the evolutionary trend of the strongest peak in the Raman spectra, a phase transition from rutile to trirutile structure at x = 0.6 was confirmed, suggesting the emergence of structural evolution. Thus, the structural evolution showed a significant impact on the dielectric characteristics, as evidenced by the weakening of the dielectric polarizability with the increasing amount of Ta⁵⁺ ion, which led to a reduction in the dielectric constant; the dielectric loss is also closely related to the packing fraction (PF) arising from the structural changes. Additionally, infrared and THz time-domain spectroscopy revealed that the dielectric losses in the microwave band were originated from the oscillatory absorption of structural phonons and supported that the effects of structural evolution on the intrinsic dielectric properties due to the introduction of Ta⁵⁺ ion.