THE GROWTH AND PERFECTION OF ORGANIC NONLINEAR-OPTICAL CRYSTALS - N-METHYL UREA (NMU) FROM METHANOL SOLUTION .2. MORPHOLOGICAL INSTABILITY

Studies of the anisotropy of the kinetics of growth of N-methyl urea ( NMU) crystals have shown that the dominant influence on the growth pro cess is volume diffusion rather than solvent-surface interactions. The consequence of this is that even at low supersaturations the crystals become morphologically unstable with the ready inclusion of solvent a nd consequent deterioration of crystal quality. This paper reports on studies of the development of this instability in order to define the conditions for the stable growth of crystals of this material for non- linear optical devices.