Department of Materials Science and Engineering, Nagoya Institute of Technology^* Nagoya University^** NEOMAX Co. LTD.,^***
○Yumi Inagaki^* Shotaro Suzuki^* Isao Kagomiya^* Ken-ichi Kakimoto^* Hitoshi Ohsato^* Katsuhiro Sasaki^** Kotaro Kuroda^** Takeshi Shimada^***

Microwave dielectric properties have been much investigated for wireless and telecommunicating applications. In particular, one kinds of band-pass-filter, high temperature superconductive filters, exhibits minimum insertion loss, which is an important for wireless communicating systems for next generations. However, there is a problem that the loss of the filters increases with dielectric loss of substrates printing strip lines. It has been found that (La_1-xSr_x)(Al_1-xTi_x)O₃ solid solutions improve the dielectric loss compared to LaAlO₃, which is a typical substrate for the HTS filters. Therefore, the single crystal of (La_1-xSr_x)(Al_1-xTi_x)O₃ is promising an appropriate substrates for high performance HTS filters. In this study, we try to prepare the single crystal of (La_1-xSr_x)(Al_1-xTi_x)O₃ (x = 0.005, 0.2) by using a floating zone method and investigate the relationship between the crystal structure and the microwave dielectric properties of the (La_1-xSr_x)(Al_1-xTi_x)O₃. As a result of the X-ray structure analysis, (La_0.8Sr_0.2)(Al_0.8Ti_0.2)O₃ exhibits the cubic (Pm-3m, A-221) structure, whereas the crystal structure of LaAlO₃ is trigonal (R-3m, A-166). It is suggested that (La_1-xSr_x)(Al_1-xTi_x)O₃ solid solutions change their crystal structures from trigonal to cubic with increasing x. In additions, we investigated the difference in crystal structure between LaAlO₃ and (La_0.8Sr_0.2)(Al_0.8Ti_0.2)O_3. We consider that the increase of the dielectric constant is related to the site volume of BO₆ octahedra and the the Q×f value is related to response for external force.