Directional growth of organic NLO crystal by different growth methods: A comparative study by means of XRD, HRXRD and laser damage threshold

摘要

Unidirectional benzophenone single crystals grown by vertical Bridgman (VB), microtube-Czochralski (μT-CZ), uniaxially solution crystallization method of Sankaranarayanan-Ramasamy (SR) were characterized using X-ray diffraction (XRD), high-resolution XRD (HRXRD), laser damage threshold (LDT) studies and the results were compared. The XRD study exhibits the growth direction of the benzophenone crystal ingots. The HRXRD curves recorded by multicrystal X-ray diffractometer (MCD) revealed that the crystals grown by all the three methods contain internal structural grain boundaries. The SR grown sample shows relatively good crystalline nature with the full-width half-maximum (FWHM) of the main peak of 39 arcsec. While, the VB grown crystal contain multiple low-angle (α ≥ 1 arcmin) grain boundaries, probably due to thermal stress during post-growth annealing caused by the difference in the lattice expansion coefficients of the crystal and the ampoule, whereas such thermal stress are absent in μT-CZ grown sample due to the free standing nature of the grown crystal. Hence, the μT-CZ grown crystals contain only one very low-angle (α < 1 arcmin) grain boundary. LDT study shows that the SR grown benzophenone crystal has higher LDT than the samples grown by other methods, probably due to relatively high-crystalline perfection of the SR grown crystals.