FAR-INFRARED REFLECTION SPECTRA OF DIELECTRIC CERAMICS FOR MICROWAVE APPLICATIONS

Far-infrared reflection spectra of dielectric ceramics, BaSm2Ti5O14, B aTi4O9, and some perovskites such as Ba(Zn1/3Nb2/3)O3, have been measu red at room temperature using a Fourier transform infrared spectromete r in order to investigate the effect of the crystal structure on the d ielectric properties. As for perovskites, Sr(Zn1/3Nb2/3)O3 and Sr(Mg1/ 3Nb2/3)O3, in which B site ions are ordered, were also measured. Refle ctance data were analyzed by means of a factorized form of dielectric functions instead of the classical dispersion theory, and all of the s pectra were well fitted. The values of dielectric constants and tan de lta calculated from the reflectance data were in good agreement with r esonant cavity measurements at 5 GHz. Furthermore, results of this stu dy have shown that the main contribution to the microwave dielectric p roperties is caused by low-frequency optically active modes located at 50 to about 300 cm-1, and for perovskite structures it is suggested t hat the ordering of B site ions is significant in obtaining low dielec tric losses.