Ryozo Kitoh

Microwave Characteristics of TiO2-Bi2O3 Dielectric Resonator

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 (er=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 er with a negative temperature coefficient and a high er 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.

Influence of Rare Earth Ions on BaO-TiO2-Rare Earth Oxide Ceramics for Microwave Applications

The dielectric ceramic materials, 0.143BaO-0.714TiO2-0.143 rare earth oxides (REOx), 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.

MICROWAVE CHARACTERISTICS OF BAPR2TI4O12 AND BAPR2TI5O14 CERAMICS

Microwave dielectric properties and microstructures of BaPr 2 Ti 4 O 12 and BaPr 2 Ti 5 O 14 ceramics which have extremely similar crystal structures, were investigated, including those of the solid solution represented by the formula of Ba 6− x Pr 8+2 x /3 Ti 18 O 54 ceramics. It is suggested that BaPr 2 Ti 5 O 14 ceramics are composed of mixed phases, approximately 85.0 vol. % Ba 4.05 Pr 9.3 Ti 18 O 54 ( 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 54 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.

Microwave characteristics of mixed phases of BaTi4O9-BaPr2Ti4O12 ceramics

The microwave characteristics of the BaTi4O9-BaPr2Ti4O12 system were investigated, including its microstructure and infrared reflection spectroscopy. It was found that this system is entirely composed of two phases, BaTi4O9 and BaPr2Ti4O12, and it is suggested that the lattices of each phase are well matched obliquely at the interface in the sintered ceramics. The dielectric properties are compared with calculated values deduced from the mixing relations of the two components. Furthermore, the infrared reflection spectra of this system were analysed with the factorized form of the dielectric function, for the purpose of studying the applicability of the reflection analysis technique to this mixed phase system.