The Effect of Bi2O3 on the structure and microwave dielectric properties of Ba6-3x Nd8+2x Ti18O54 System(x=2/3)

Abstract

The structures and dielectric properties of Ba6−3xNd8+2xTi18O54 system(x=2.3) doped with different contents of Bi2O3, whose final molecular formula is Ba6−3x(Nd1−yBiy)8+2xTi18O54 were investigated. It is indicated that the dielectric constant increases greatly whereas Q value( f0=4 GHz) decreases with the increase of Bi2O3 content. However, the temperature coefficient could be controlled below 0±30×10−6/°C in the experiment. These phenomena are related to the appearance of a new phase, Bi4Ti3O12, which has high dielectric constant. Also, that Bi3+(0.13 nm) substitutes for Nd3+(0.099 5 nm) will increase the unit cell volume, which will lead to the enlargement of the octahedron B site occupied by Ti4+. So the spontaneous polarization of Ti4+ ions will be strengthened. Besides, Bi3+ will fill up some vacancies which Ba2+ or Nd3+ ions leave in two A1 sites and four A2 sites. More positive ions polarize, which also contributes to higher dielectric constant. The samples got with the optimium properties are sintered at 1 200 °C for 4 h, when y=0.25, e≈.110, Q≈5 400(f0=4 GHz), TCC=−4.7× 10−6/°C; When y=0.3, e≈120, Q≈5 000(f0=4 GHz), TCC=−24×10−6/°C.