The Czochralski growth of large-diameter La_3Ga_(5.5)Ta_(0.5)O_(14) crystals along different orientations

摘要

La_3Ga_5SiO_(14), La_3Ga_(5.5)Ta_(0.5)O_(14) and La_3Ga_(5.5)Nb_(0.5)O_(14) crystals exhibit outstanding piezoelectric properties. They are of considerable interest for high-precision resonators. Although the synthesis of these crystals has been actively pursued over the past years, there are still some setbacks slowing down industrial applications. We report on the growth of La_3Ga_(5.5)Ta_(0.5)O_(14) (LGT) crystals by the Czochralski growth along < 001 >, < 100 > and < 120 >. These crystals were characterized by different techniques, including X-ray synchrotron topography. LGT crystals show a facet structure which determines the overall 3D distribution of other defects and strain. The relationship between faceting and crystal imperfections such as striations, dislocations, and inclusions will be discussed. After optimization of growth conditions, inclusions-free, colorless transparent single crystals with a diameter of 2″ were obtained. These crystals were processed into Y-cut plano-convex resonators, and the Qf product measured from fundamental to ninth overtone. Values exceeding the limit of AT- and SC-cut quartz were obtained.