Effect of 0.2wt% Bi₂O₃, CuO, B₂O₃ on the properties of 5Ca_0.6La_0.267TiO₃-5Ca (Mg_1/3Nb_2/3)O₃ microwave Dielectric ceramics

The effects of 0.2wt% Bi₂O₃, CuO, B₂O₃ additions on the microwave dielectric and sintering properties of 5Ca_0.6La_0.267TiO₃-5Ca (Mg_1/3Nb_2/3)O₃ ceramics prepared by conventional solid-state route were investigated. The generation of liquid-phase resulted from the addition of Bi₂O₃, B₂O₃ and CuO effectively decreased the sintering temperature. The addition of Bi₂O₃ and CuO did not influence the grain morphology of the specimens and with the increase of sintering temperature, the dielectric constants and quality factors both shifted the same variation as that of density, which reach the maximum when the specimens have the highest density. Small amount of columnar grains appear in specimens doped with 0.2wt%B₂O₃ when the sintering temperature reaches 1300°C and the amount of the columnar crystals increases with increasing sintering temperature. The significant increase of Q×f values for B₂O₃ doped specimens may be related to the formation of columnar grains. However, when sintered at 1350°C, excessive columnar grains resulted in the decrease of Q×f values. The addition of Bi₂O₃, B₂O₃ and CuO has little effect on the phase composition, so no significant variation in the τf values for the specimens was observed. The 5CLT-5CMN ceramics doped with 0.2wt%B₂O₃ and sintered at 1325°C have the optimal microwave dielectric properties: ε_r=54.87, Q×f=55726 GHz, τ_f=-0.6 ppm/°C.