The Effect of Bi₂O₃ on the structure and microwave dielectric properties of Ba_6-3xNd_8+2xTi₁₈O₅₄ System(x=2/3)

Abstract

The structures and dielectric properties of Ba_6−3xNd_8+2xTi₁₈O₅₄ system(x=2.3) doped with different contents of Bi₂O₃, whose final molecular formula is Ba_6−3x(Nd_1−yBi _y)_8+2xTi₁₈O₅₄ were investigated. It is indicated that the dielectric constant increases greatly whereas Q value( f ₀=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, ε≈.110, Q≈5 400(f ₀=4 GHz), TCC=−4.7× 10⁻⁶/°C; When y=0.3, ε≈120, Q≈5 000(f ₀=4 GHz), TCC=−24×10⁻⁶/°C.

Keywords

BNT / Bi₂O₃ / dielectric constant / temperature coefficient / Q value

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