Structures and microwave dielectric properties of Ba_6−3x(Nd,Bi_y)_8+2xTi₁₈O₅₄x = 2/3) solid solution

Abstract

The effects of Bi substitution for Nd in Ba_6−3xNd_8+2xTi₁₈O₅₄x = 2/3) solid solution upon the microstructures and microwave dielectric properties were investigated. The solid solubility limit of Bi in Ba_6−3xNd_8+2xTi₁₈O₅₄x = 2/3) solid solution was about 15 mol%, the same as that for x = 0.5, and densification of the present solid solutions could be performed well at lower temperatures. However, the variation tendency of microwave dielectric properties with composition in the present ceramics quite differed from that for x = 0.5: (1) The temperature coefficient of resonant frequency in the present ceramics showed a continuous variation from positive to negative and did not indicate extreme value at the solid solubility limit. (2) Near-zero temperature coefficient of resonant frequency combined with high-ε and high-Qf values could be obtained in the present ceramics, while that for x = 0.5 had a lower limit of +15 ppm/°C. (3) The dielectric constant also showed a continuous increase for the present compositions, while that in x = 0.5 had an extreme at solid solubility limit. Ceramics with composition of Ba_6−3x(Nd_0.85,Bi_0.15)_8+2xTi₁₈O₅₄x = 2/3) showed excellent dielectric properties of ε = 99.1, Qf = 5290 GHz, and τ_f = −5.5 ppm/°C.