Enhanced Q×f in CoTi(Nb1-xVx)2O8 ceramics by tuning oxygen vacancy concentration and Co valence state

Abstract

V cation was introduced at Nb-site in CoTiNb₂O₈ for the purpose of tuning the defects concentration. XRD analysis indicated that no secondary phase developed over the whole composition range. The sintering temperature decreased to 1150 °C in current work, compared with pure CoTiNb₂O₈ ceramic (∼1250 °C). V-introduction inhibited grain growth and benefited grain homogenization. The decreased molecular dielectric polarizability and blue shift of Raman A_1g mode both made lower ε_r from 59.2 to 41.8. Based on the X-ray photoelectron spectroscopy (XPS), V doping decreased the oxygen vacancy concentration and tuned the Co valence state. The defects compensation by oxygen and Co vacancies significantly improved Q × f up to 38,012 GHz, accompanied with a 50 % rise. The slight increase in τ_f was attributed to the Nb–O bond energy reduction. The CoTi(Nb_0.97V_0.03)₂O₈ had a high ε_r of 54.6 with good Q × f of about 38,012 GHz and τ_f = 96.47 ppm/°C. Enhanced Q × f and low sintering temperature were achieved simultaneously.