Characterization of growth defects in piezoelectric single crystals by synchrotron white beam X-ray topography

Growth defects in piezoelectric single crystals, langasite (La3 Ga5SiO14 or LGS) and its two isomorphs langanite (La3Ga5.5Nb0.5O14 or LGN) and langatate (La3Ga5.5Ta0.5O14 or LGT), along with quartz, were characterized by synchrotron white beam X-ray topography (SWBXT) and complemented by optical microscopy and other characterization techniques.; A systematic study of LGS, LGN and LGT crystals, grown by Czochralski technique, at different stages throughout the whole device-making process, from as-grown boules to the packed resonators, was carried out by SWBXT. A detailed growth defect configuration was established. It was found that the most dominant defect in these crystals is the growth striations. Core structure, with concentration of growth dislocations, served as the origin of almost all cracking in the crystals. Precipitates were distributed all over the crystal with higher density at the beginning and ending of the growth process.; Two origins of the striations, thermal striations due to growth rate variation and kinetics striations induced by faceting, were identified. The 3D configuration of thermal striations was presented and correlated to the growth interface during the crystal growth. A theoretical analysis, by analogizing to the segregation phenomena, attributed the origin of thermal striations to the temperature fluctuation in the melt. Using a combination of various X-ray diffraction conditions, it was revealed that the X-ray topography contrast of thermal striations was associated with dynamical diffraction effects due to the slight lattice distortion, which was primarily along the growth direction. Strong tendency of faceting on different planes resulted in kinetics striations of different configurations. Results revealed the correlation between faceting and the formation of core structure as well as the change of growth interface morphology.; Defect distribution of quartz bars, blanks and resonators were examined, and common defects were identified by SWBXT. It was concluded that quartz crystals should be routinely screened to prevent the defects being transformed into the devices. It was discovered that strains introduced by bonding of the pins have great impact on the quality of the quartz resonators. In the study of twinning in quartz, SWBXT was employed to determine the displacement vectors and solve the structure of the Brazil twin boundary.