INTRODUCTION

Large crystals with a high degree of perfection are required in a variety of applications. Optical crystals of good quality find utility in critical technology areas such as high power lasers, higher harmonic generation and in nuclear fusion.  A  class  of  such crystals can be  grown  from  their supersaturated  solution  in  water, during  a  slow   cooling process. Growth of such crystals from an aqueous solution is one of the commonly used techniques in the industry. The technique can be used for growing optical crystals such as KDP and proteins such as lysozyme. A crystal growing from its aqueous solution creates a three-dimensional solute distribution in its vicinity. The solutal concentration gradients and hence the gradients in the density of the solution are responsible for the evolution of buoyancy-driven convection currents in the growth chamber. The buoyant convection currents influence the magnitude of the concentration gradients prevailing along   the   growth surfaces. In turn these control the stability of the growth   process and the overall crystal quality. The concentration gradients in the growth chamber are significantly altered when the crystal is given rotation. Rotation can hence be viewed as a method of controlling convection during the growth process.

Low temperature solution growth methods are applicable to materials that have moderate to high solubility in temperatures up to at atmospheric pressure. A number of organic and inorganic materials fall in this category and can be crystallized using this technique. The advantages here include relatively low temperature handling of the equipment and a good degree of temperature control to within . The grown crystals show full natural morphology. In addition, online studies of surface growth features and growth rate studies of different faces are possible. Since temperature gradients involved in a given process are low, thermally generated strains in the grown crystal are small. The disadvantage of low temperature solution growth is the slow growth rates (0.1 to 10 mm per day). In many cases the ease of solvent inclusion into the growing crystal is a limiting factor. Since many crystals are grown from water as the solvent, the grown crystal is hygroscopic in nature; this limits its use to applications in which water molecules are excluded in the lattice. A large fraction of the crystals produced from low temperature solutions are grown by using water as a solvent owing to its high solvent action, chemical stability, low viscosity, low toxicity and low cost. Other solvents include ethanol, methanol, acetone, carbon tetrachloride, hexane, and xylene. Examples of technologically important crystals grown from a low temperature aqueous solution include potassium di-hydrogen phosphate (KDP), potassium di-deuterium phosphate (DKDP), tri-glycine sulphate (TGS), potassium acid phthalate (KAP), lithium arginine phosphate (LAP), and urea. Recently, low temperature solution growth method has found its applications towards the growth of protein crystals such as lysozymes.