Microwave dielectric properties of Ba6-3xLa8+2x(T1-zZrz)18O54 (x=2/3) ceramics

Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2x(Ti1-zZrz)(18)O-54(x=2/3) ceramics. A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0<z<0.2 in Ba6-3xLa8+2x(Ti1-zZrz)(18)O-54 ceramics. As Zr content exceeded this range, a secondary phase of Ba2ZrO4 was detected. This is correlated with the decrease of tolerance factor. As Zr content increased, there was an expansion of the b-axis and c-axis, and increase in the cell volume. Incorporation of small levels of Zr into the structure led to a significant increase in Q.f values, from 2053 to 6665 a decrease in dielectric constant (epsilon(r)) from 107.4 to 79.6 and the temperature coefficient of resonant frequency (tau(f)) slightly improved. The maximum value of Q.f (6665 GHz, f=4.83 GHz) was achieved while Er was 79.6 and tau(f) was 109.83x10(-6)degrees C-1 for z=0.1. Microstructure studies with SEM indicated that the ceramics with larger and homogenous columnar grains had high Q.f value.