Sintering behavior, microwave dielectric properties and thermally stimulated depolarization current behavior of B₂O₃-doped CoTiNb₂O₈ ceramics

Low-fired B₂O₃-doped CoTiNb₂O₈ (CTN) microwave dielectric ceramics were synthesized via the conventional solid-state reaction method. The effects of B₂O₃ on the sintering behavior, phase composition, crystal defects and microwave dielectric properties of CTN ceramics were studied systematically. The B₂O₃ additive could effectively lower the sintering temperature from 1250 to 1000 °C. Single tetragonal rutile phase was found for all samples tested. Room-temperature microwave dielectric properties at high frequency and temperature-dependent dielectric properties at low frequency were both studied. It was found that B₂O₃ could induce obvious dielectric relaxation which was largely linked to the oxygen vacancy ($V_{\text{O}}^{\bullet \bullet }$). Also, newly formed defect dipole ($2T{i}_{\text{Ti}}^{\prime }-V_{\text{O}}^{\bullet \bullet }$) was detected by thermally stimulated depolarization current measurement. These two kinds of defects were both responsible for the dielectric loss of CTN ceramics. When the amount of B₂O₃ addition was 3 wt%, CTN ceramics sintered at 1000 °C possessed the optimum microwave dielectric properties with a ε_r of 63.4, a high Q × f of 18,793 GHz, and a τ_f of 80.48 ppm/°C, and was a promising candidate for low-temperature cofired ceramic (LTCC) applications.