MICROWAVE DIELECTRIC PROPERTIES OF Ba0.75Sr0.25 (NdxBi1-x)2Ti4O12 SOLID SOLUTION

This work investigated the influences of Bi content on the phase structure, phase composition, microstructure and microwave properties of tungstenbronze-type like Ba0.75Sr0.25(NdxBi1-x)(2)Ti4O12 ceramics. XRD patterns showed that the main crystal phase of the ceramics with different Bi content (0.75 <= x <= 0.9) sintered at 1250 degrees C to 1400 degrees 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 : (l-x)) is 3:1 namely x is 0.75(B13), this ceramic shows optimum dielectric properties with a high dielectric constant (epsilon) of 118.5, a quality factor (Q x f) of 4907 (f = 2.8 GHz), and a temperature coefficient of resonant frequency tau(f) = -1.3 ppm/degrees C. As the addition of Bi increased from 0.1 to 0.25, the value of epsilon markedly increased, the value of Q x f and tau(f) decreased with a tau(f) value finally approaching to zero.