Characterization of low angle grain boundary in large sapphire crystal grown by the Kyropoulos method

Low angle grain boundaries (LAGB) are one of the most commonly seen defects in sapphire crystals. In this paper, we have studied the origin, topography and orientation of LAGB in large sapphire crystals grown by the Kyropoulos method through etching, polaroscopy, optical microscopy as well as synchrotron white-beam X-ray topography. The results show that the LAGB starts mainly from the atomic layers mismatch caused by environmental fluctuations. The misorientation angle of the grain boundaries is 2-3°, and the grain boundaries are distributed around 〈101¯0〉 direction.