The microwave characteristics of the binary-system TiO2-Bi2O3 ceramics, which is widely known to exhibit a comparatively high dielectric constant in the lower-frequency band, are investigated from a new standpoint. It is shown in this article that the composition of 0.919TiO2-0.081Bi2O3 has a high dielectric constant (εr=80), high Q (1800 at 5 GHz) and low temperature coefficient of resonant frequency (τf=+21 ppm/°C). From the X-ray diffraction and X-ray microanalysis, it is indicated that the crystal structure of this material is composed of two phases, TiO2 and Bi2Ti4O11, which possess a high εr with a negative temperature coefficient and a high εr with a positive temperature coefficient, respectively. The measurements of linear thermal expansion and temperature coefficient of capacitance are also carried out in order to study the behavior of temperature compensation in this system.

Far-infrared reflection spectra of dielectric ceramics, BaSm,Ti,O,,, BaTi,O,, and some perovskites such as Ba(Zn,,Nb,)O,, have been measured at room temperature using a Fourier transform infrared spectrometer in order to investigate the effect of the crystal structure on the dielectric properties. As for perovskites, Sr(Zn,,NbU,)O, and Sr(Mg,,Nb,)O,, in which B site ions are ordered, were also measured. Reflectance data were analyzed by means of a factorized form of dielectric functions instead of the classical dispersion theory, and all of the spectra were well fitted.The values of dielectric constants and tan 6 calculated from the reflectance data were in good agreement with resonant cavity measurements at 5 GHz. Furthermore, results of this study have shown that the main contribution to the microwave dielectric properties is caused by low-frequency optically active modes located at 50 to about 300 cm-', and for perovskite structures it is suggested that the ordering of B site ions is significant in obtaining low dielectric losses.

The dielectric ceramic materials, 0.143BaO-0.714TiO2-0.143 rare earth oxides (REO x ), have unique dielectric properties at microwave frequencies, which depend on the rare earth element (RE=Pr, Nd, Sm). In order to study the effect of the rare earth ions on dielectric properties, infrared reflection spectra of these ceramics were measured from 50 to 4000 cm-1 at room temperature. These data were analyzed according to the model proposed by Gervais and Piriou. Also, the fourth-order dielectric constants of these materials were estimated for the purpose of investigating the relationship between the dielectric loss and the anharmonic terms in the potential energy.

5 Oi4 ceramics which have extremely similar crystal structures, were investigated, including those of the solid solution represented by the formula of Ba 6 _ ;c Pr 8+ 2^3Ti 18 054 ceramics. It is suggested that BaP^TisO^ ceramics are composed of mixed phases, approximately 85.0 vol. % Ba4.o5Pr9. 3 Tii 8 0 5 4 (x = 1.95), 8.1 vol. % TiO 2 , and 6.9 vol. % BaTi 4 O 9 . The microwave dielectric properties of the Ba 6 _ x Pr 8+ 2 X / 3 Ti 18 O 5 4 system are strongly dependent on the x value, which is interesting for studying the relationship between microstructures and dielectric properties. Far infrared reflection spectra were also measured to study the mixed phases formed in these ceramics in more detail.

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