Site occupancy of Bi ions and microwave dielectric properties in Ba6−3xNd8+2xTi18O54 solid solutions

The tungstenbronze-type like Ba6−3xR8+2xTi18O54 (R=rare earth) solid solutions have excellent microwave dielectric properties. In particular, Nd-system materials have high dielectric constant (εr) around 80 and high quality factor (Q · f) near 10 000 GHz. However, the temperature coefficients of the resonant frequency, τf, is very poor, 63 ppm °C−1 for use as practical microwave material. We have investigated the effects of substituting Bi ions in Ba6−3xR8+2xTi18O54 (x=2/3) solid solutions in terms of the lattice parameters, and phase structures. It seems that until y=0.05, Bi ions substituted for Ba ions. Thereafter, Bi ions substituted for Nd ions from y=0.05 to 0.3. As y increased, the dielectric constant, εr, increased and the quality factor, Q · f, decreased. The temperature coefficients of the resonant frequency, τf, improved to 17 ppm °C−1 at y=0.15.