Kensuke Wada

Grain-Orientation Control and Microwave Dielectric Properties of Ba4Sm9.33Ti18O54 Ceramics

The effects of grain orientation on the microwave dielectric properties of Ba4Sm9.33Ti18O54 (BST) ceramics have been investigated. Grain-oriented ceramics were fabricated by a templated grain growth (TGG) technique. Columnar BST template particles synthesized via a molten salt route were aligned by tape casting in a mixture of calcined BST powder. The sintered BST ceramics exhibited elongated c-axis grain growth parallel to the casting direction. Orientation degree of the sintered BST ceramics increased with the content of template particles up to 10 wt%. High anisotropy in the temperature coefficient of resonant frequency (τf) was found between the parallel and perpendicular directions to the casting direction. Moreover, τf varied in proportion to the orientation degree. This result suggests that grain-orientation control is one of the useful techniques for control of τf.

Microwave dielectric properties of textured BaLa4Ti4O15 ceramics with layered perovskite structure

Textured ceramics of BaLa4Ti4O15 (BaLT) with layered perovskite structure have been investigated by characterizing their dielectric properties at MHz and GHz frequencies. The highly grain-oriented ceramics were obtained by a templated grain growth technique. Hexagonal {001}-platelet BaLT particles prepared in molten salt were used as the template. The sintered ceramics containing template powders of 10 wt % exhibited a degree of -orientation of 80% for the casting plane, whereas the plane perpendicular to the casting direction showed a degree of -orientation of 76%. The effect of grain orientation on the dielectric properties was observed as an anisotropy between the directions of parallel and perpendicular to the c-axis. As a result of the anisotropy, enhanced microwave dielectric properties (er=53, Qf=41,400 GHz and τf=-1 ppm/°C) compared with those of a randomly oriented ceramics were obtained in the TE011 mode for a cylindrical specimen with a {001} grain-orientation in the circular plane.

Anisotropic Microwave Dielectric Properties of Textured Ba4 Sm9.33 Ti18 O54 Ceramics

Dielectric anisotropy of textured Ba4Sm9.33Ti18O54 (BSmT) ceramics have been investigated. Highly textured ceramics were fabricated by “templated grain growth” process. Columnar BSmT particles prepared by molten salt synthesis were used as template and aligned by tape casting in a mixture of matrix BSmT powder. The sintered ceramics exhibited uniaxial grain orientation parallel to the casting direction. The effect of grain-orientation in the dielectric constant and quality factor was small, whereas temperature coefficient of resonant frequency (τf) was markedly varied in proportion to the orientation degree. The opposite behavior in temperature dependence of dielectric constant was observed between ab-direction and c-direction. The change of τf was explained based on the relationship between the distribution of the electric field in the TE01δ resonant mode and grain orientation.

Control of temperature coefficient of resonant frequency in Ba4Sm9.33Ti18O54 ceramics by templated grain growth

Abstract A novel tuning method of temperature dependence of dielectric properties in Ba4Sm9.33Ti18O54 (BSmT) microwave material was demonstrated by texture engineering. Two kinds of grain-oriented BSmT ceramics were obtained using a templated grain growth technique. Highly fiber-textured ceramics were fabricated by tape casting of slurry with a mixture of 〈001〉-elongated BSmT template particles and fine-grained BSmT powder. On the other hand, partially grain-oriented ceramics were also obtained from the uniaxially pressed mixture of the template particles and the fine-grained powder. Orientation degree of sintered BSmT ceramics increased with a content of template particles. As compared with the specimen prepared by normal sintering technique, the textured ceramics displayed a large anisotropy in the dielectric properties, especially in the temperature coefficient of resonant frequency (tf). Consequently, near-zero tf was obtained in the textured ceramics with (hk0)-orientation degree of approximately 0.10 in the surface of the disk specimen. In addition, the tf could be controlled to a desired value from ranging K90 to C25 ppm/8C by adjusting the grain orientation in the specimen. Measurement of the temperature dependence of dielectric constant, which correlates with tf, revealed positive and negative behaviors for (hk0) and (001) textured BSmT ceramics, respectively. The tuning of tf was explained as a rule of mixture of dielectric anisotropy in BSmT.