Seeded supercooled melt growth and polar morphology of organic nonlinear optical crystal, meta-nitroaniline (mNA)

Abstract

We report the seeded growth of meta-nitroaniline (mNA) crystal from the 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 the metastable zone. The melt was stirred mechanically and the crystal was 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 grown for a period of one day. The overall morphology of supercooled melt grown mNA crystals is represented by the unidirectional growth along the one direction of the polar axis. The absolute direction of preferred 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-facetted 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 optical characterization was made by measuring second harmonic conversion efficiency and laser damage threshold. (C) 1998 Elsevier Science B.V. All rights reserved.