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

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 (τf). Consequently, near-zero τf was obtained in the textured ceramics with (hk0)-orientation degree of approximately 0.10 in the surface of the disk specimen. In addition, the τf could be controlled to a desired value from ranging −90 to +25 ppm/°C by adjusting the grain orientation in the specimen. Measurement of the temperature dependence of dielectric constant, which correlates with τf, revealed positive and negative behaviors for (hk0) and (001) textured BSmT ceramics, respectively. The tuning of τf was explained as a rule of mixture of dielectric anisotropy in BSmT.