Infrared reflection spectra of Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54) (x=0.5, 0.67, and 0.75) microwave dielectric ceramics

摘要

Infrared reflection spectra of the tungsten bronze-type Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54) (x=0.5, 0.67, and 0.75) ceramics were measured and analyzed by a combined method using Kramers-Kroning relation and the classical oscillator model, and the selection rules and vibration modes of the tungsten bronze-type structure were investigated by a detailed group theory analysis. Microwave dielectric properties were calculated using the dispersion parameters obtained by the classical oscillator model. The error in reflectance due to the random scattering on sample surfaces indicated obvious effect on the calculated dielectric constant, but only slightly influenced the calculated Qf, and therefore, the present analysis provided a reasonable means to predict the intrinsic microwave dielectric loss. The predicted intrinsic Qf values ( > 30 000 GHz) were much higher than the experimental ones (～10 000 GHz), and this suggested the great potential of significant improvement of Qf value in Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54) ceramics by controlling the extrinsic dielectric loss.