SEEDED SUPERCOOLED MELT GROWTH AND POLAR MORPHOLOGY OF ORGANIC NONLINEAR-OPTICAL CRYSTAL, META-NITROANILINE (MNA)

We report the seeded growth of meta-nitroaniline (mNA) crystal from th e supercooled melt. A seed was introduced into the purified mNA melt 0 .1 degrees C above the melting temperature (T-m = 112.0 degrees C) and crystal was grown at constant supercooling of 0.1 degrees C within th e metastable zone. The melt was stirred mechanically and the crystal w as also forced to rotate while the growth proceeded. mNA crystals of a size up to 20 x 15 x 15 mm(3) and of very high perfection could be gr own for a period of one day. The overall morphology of supercooled mel t grown mNA crystals is represented by the unidirectional growth along the one direction of the polar axis. The absolute direction of prefer red growth was determined to be [0 0 (1) over bar] by the pyroelectric measurements. The faces of the bottom half of the crystal are well-fa cetted and covered by {1 1 (1) over bar} and {0 2 (1) over bar} faces, while the faces of the top half are not well defined. The perfection of the crystal was characterized by synchrotron X-ray topography and o ptical characterization was made by measuring second harmonic conversi on efficiency and laser damage threshold. (C) 1998 Elsevier Science B. V. All rights reserved.