Crystal structure analysis and microwave dielectric properties of LaAlO3-SrTiO3 solid solutions

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 (La1-xSrx)(Al1-xTix)O3 solid solutions improve the dielectric loss compared to LaAlO3, which is a typical substrate for the HTS filters. Therefore, the single crystal of (La1-xSrx)(Al1-xTix)O3 is promising an appropriate substrates for high performance HTS filters. In this study, we try to prepare the single crystal of (La1-xSrx)(Al1-xTix)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 (La1-xSrx)(Al1-xTix)O3. As a result of the X-ray structure analysis, (La0.8Sr0.2)(Al0.8Ti0.2)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 (La1-xSrx)(Al1-xTix)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 (La0.8Sr0.2)(Al0.8Ti0.2)O3. 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.