THE GROWTH, PERFECTION AND PROPERTIES OF ORGANIC NONLINEAR OPTICAL-MATERIALS .1. 4-NITRO-4'-METHYL BENZYLIDENE ANILINE

Single crystal specimens of the organic non-linear optical material 4-nitro-4'-methyl benzylidene aniline (NMBA) have been grown from the melt (Bridgman technique) and from solution (slow cooling technique). Crystals produced by the former technique were strained, principally due to the instability of the material in the melt and the tendency of the decomposition products to accumulate in the solid during growth. Crystals grown from solution were of much higher perfection exhibiting the forms: (010), {111}, {011} (all dominant) and (102BAR), (100) (less dominant) predicted by theoretical calculations of the equilibrium form. The rhombic shaped crystals which occasionally contained striations parallel to the (102BAR) plane were grown to sizes of 5 x 3 x 0.5 cm3 (maximum dimensions). Large volumes of the crystals were optically clear and unstrained. From these could be prepared cut and polished specimens (0.5 x 0.3 x 0.2 cm3) for structural and optical assessment.