Crystal structure and microwave dielectric properties of SrTiO_3 doped LaALO_3 single crystal grown by FZ

摘要

(La_(1-x)Sr_x)(Al_(1-x)Ti_x)O_3 solid solutions reveal higher quality factor (Q X f) than that of pure LaAlO_3. We propose the use of (La_(1-x)Sr_x)(Al_(1-x)Ti_x)O_3 single crystals for a substrate of high temperature superconductive (HTS) filters. The single crystal of the (La_(1-x)Sr_x)(Al_(1-x)Ti_x)O_3 (x = 0.005, 0.2) was grown by using a floating zone (FZ) method to investigate the relationship between the microwave dielectric properties and the crystal structure. Analysis of the grown (La_(0.8)Sr_(0.2))(Al_(0.8)Ti_(0.2))O_3 crystal was performed using a X-ray diffraction method. Although the crystal structure of pure LaAlO_3 is trigonal (R3m, no. 166), the SrTiO_3 doped LaAlO_3 had stabilized cubic symmetry (Pm3m, no. 221), which corresponds to high temperature phase of pure LaAlO_3. The refined structure of (La_(0.8)Sr_(0.2))(Al_(0.8)Ti_(0.2))O_3 exhibited ideal perovskite structure with the angle between O-B-O of 90.0 deg. This is related to improvement of Q X f value of LaAlO_3.