Evelyn E. A. Shepherd

The growth and perfection of organic non-linear optical crystals: N-methyl urea (NMU) from methanol solution. III. The growth of large single crystals for optical examination

Using growth conditions defined from previous studies of the kinetics of growth of this material, large crystals of N-methyl urea (NMU) have been prepared by seeded solution growth using the temperature lowering technique. The principal constraints to good growth are that crystals should be prepared using seeds cut from good quality crystals previously prepared by this technique and that they should be developed under conditions of low supersaturation (σ < 0.5−3%). Efficient stirring conditions should be used with flow reversal to minimise the effect of volume diffusion and macrostep formation which in turn leads to the inclusion of solvent in some sectors. The role of seed orientation in the definition of the development process is discussed. Under well-defined conditions of seed orientation and development crystals of dimensions 5 × 4 × 4 cm3 have been produced of high optical and structural perfection and with efficient non-linear optical performance. This material shows a figure of merit performance which improves on urea. For the doubling of light of wavelength 871.6 nm; d14 ≈ 2pm V−1, cf. urea d14 = 1.7pm V−1.

The growth, perfection and properties of organic non-linear optical materials I. 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 (102), (100) (less dominant) predicted by theoretical calculations of the equilibrium form. The rhombic shaped crystals which occasionally contained striations parallel to the (102) plane were grown to sizes of 5x3x0.5 cm3 (maximum dimensions). Large volumes of the crystals were optically clear and unstrained. From these could be prepared cut and polished specimens (0.5×0.3×0.2 cm3) for structural and optical assessment.

Morphological evaluation of the γ-polymorph of indomethacin

Abstract A study has been made of the polymorphic nature of crystals of the pharmaceutical indomethacin grown from a wide range of solvents and from the melt. In most solvents, growth at high supersaturations yielded either a 1:0.5 solvated form (approximately) or the α-polymorph. At low supersaturations the γ-polymorph was commonly produced. Solutions in MeOH and t BuOH yielded a 1:1 solvate. The morphology of the γ-form showed no variation with solvent type but changed with supersaturation in a manner consistent with a differential variation in growth rates of the faces. This lack of solvent influence was confirmed by the fact that a similar morphology resulted on growth from the melt. Morphology predictions were carried out for the γ-polymorph and these show good agreement with experimental observations.

The growth of large single crystals of the organic nonlinear optical material 2-(α-methylbenzylamino)-5-nitropyridine

The crystal growth behaviour of the important organic nonlinear optical material 2-(a-methylbenzylamino)-5-nitropyridine (MBANP) (space group P21) has been investigated and techniques have been developed for the preparation of large (up to 7 cm x 4 cm x 3 cm) high-quality single crystals suitable for detailed optical, dielectric, ultrasonic and piezoelectric studies and for device fabrication. Observation of the crystal growth behaviour and measurement of growth kinetics revealed a strong and anomalous dependence of growth rate on supersaturation. At relative supersaturations less than 0.08, slow growing irregular faces were formed. Once the crystal was completely bounded by such faces, little or no further growth occurred. At supersaturations below 0.24 no growth was observed in either <010> direction. Above this, rapid, but highly imperfect, growth occurred in one <010> direction while the opposite end of the crystal exhibited zero growth rate at all achievable supersaturations. At relative supersaturations greater than 0.4 considerable instability in the growth along [010] was observed. The factors potentially responsible for this behaviour are discussed. A novel technique is described for the preparation of seed crystals elongated parallel to <010>. The use of such seeds allows the growth of large crystals of MBANP at supersaturations less than 0.24, thereby avoiding the highly imperfect and unstable growth at higher supersaturations and yielding crystals of very high quality. The nature, density and distribution of growth induced defects in large crystals of MBANP have been investigated using X-ray diffraction topography. In addition to revealing growth dislocations, growth sector boundaries, inclusions and striations, these studies provide a detailed insight into the growth history of the crystals.

The crystal growth behaviour of the organic non-linear optical material 2-(α-methylbenzylamino)-5-nitropyridine (MBANP)

Observation of the growth behaviour and measurement of the growth kinetics of 2-(α-methylbenzylamino)-5-nitropyridine (MBANP) has revealed a strong and anomalous dependence of growth rate on supersaturation. At relative supersaturations less than 0.08, slow growing irregular faces were formed. At supersaturations below 0.24 no growth was observed in either 〈010〉 direction. Above this, rapid, but highly imperfect, growth occurred in one 〈010〉 direction while the opposite end of the crystal exhibited zero growth rate at all achievable supersaturations. The factors potentially responsible for this behaviour are discussed. On the basis of these observations, techniques have been developed for the preparation of large (up to 7 x 4 x 3 cm 3 ) high quality single crystals suitable for detailed optical studies and for device fabrication.

Crystal growth and characterisation of the electro-optic material 3-(2,2-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole

The growth of 3-(2,2-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole crystals from toluene and ethyl acetate solutions is described. Kinetic data indicate the development of a polar morphology due to anisotropic solvent adsorption. A double-solvent technique has been used to grow crystals up to 1 cm2 in cross-section and their perfection was examined by X-ray section topography.

Theoretical and experimental morphologies of 4-aminobenzophenone (ABP) crystals

The lattice energy (Elatt), slice energies (Eslice) and attachment energies (Eatt) of the different habit faces of ABP crystals have been calculated using the computer program HABIT. On the basis of the attachment energies of different crystal faces, the morphology was defined as {1 0 0}, {0 0 1}, {1 1 0}, {11¯0} and {1 01¯}. To confirm this theoretical prediction, we have grown ABP films and ABP crystals from the vapour phase. In both cases, the morphologically most important face was defined as {1 0 0} face using X-ray diffraction techniques. The remaining faces of the vapour-grown crystals were defined using a projection method, while the crystallites in the films were morphologically analysed by means of atomic force microscopy (AFM). The experimental morphologies are basically in agreement with the computation. Deviations from the equilibrium morphology can be ascribed to departure from equilibrium conditions during growth. For completeness, the results are compared with those for crystals grown from solutions for which deviations in morphology from the theoretical predictions can be ascribed to interaction between the crystal faces and solvent molecules.