Ceramics-Silikáty 55, (4) 373 - 377 (2011)

This work investigated the influences of Bi content on the phase structure, phase composition, microstructure and microwave properties of tungstenbronze-type like Ba_0.75Sr_0.25(Nd_xBi_1-x)₂Ti₄O₁₂ ceramics. XRD patterns showed that the main crystal phase of the ceramics with different Bi content (0.75 ≤ x ≤ 0.9) sintered at 1250°C to 1400°C for 3 h was BaNd₂Ti₄O₁₂ with small amount of second phase Ba₂Ti₉O₂₀. SEM photographs suggest that Bi could work as sintering aids promoting the densification and grain growth. In the case of the ratio of Nd and Bi (x : (1-x)) is 3:1 namely x is 0.75(B13), this ceramic shows optimum dielectric properties with a high dielectric constant (ε) of 118.5, a quality factor (Q × f) of 4907 (f = 2.8 GHz), and a temperature coefficient of resonant frequency τ_f = –1.3 ppm/°C. As the addition of Bi increased from 0.1 to 0.25, the value of ε markedly increased, the value of Q × f and τ_f decreased with a τ_f value finally approaching to zero.