Research On The Rapid Growth Mechanism Of KDP-type Crystal

KDP-type (KH2PO4) crystal is a kind of non-linear optical material with excellent character. KDP-type crystals are the only nonlinear crystals currently used for laser inertial confinement fusion due to their exclusive physical properties. The traditional growth method of KDP has not met the practical requirements. The rapid growth technique developed in recent years was quite different from the traditional slow growth from technology to the theory. Rapid growth technology breaks the concepts of slow rate of applied crystal growth, and brings new challenges to the study crystal growth technology and theory. Many new phenomena appeared in the process of rapid growth need to be explained. In this paper, KDP-type crystal growth process was in-depth study from rapid-growth mechanism of KDP-type crystal.An in-situ crystal growth microscopic observation system was designed and built. The rapid growing surface morphology evolvement of {100} and {101} faces of KDP crystals were observed and recorded by the system. It was found that KDP crystals grown in the form of layers under high supersaturation condition; Comparing to {100} face, {101} face began to grow in the form of layers under lower superaturation (abouto=4%); Kinetic parameters of {100} and {101} face were different from each other. The {100} growing surface of KDP crystals were ex situ investigated by atomic force microscopy. The steps height and terraces width of macroscopic steps were measured. Step-bunching and Step-disordered caused by impurities were observed on {100} surface. The cause of Step-bunching was analyzed.The growth mechanism in the regeneration of Z-cut ADP crystal was explored by analyzing the growth of thin surface layers formed. The curves of the thin surface layer growth velocity with supersaturation were measured, and corresponding kinetics coefficients were calculated by the formula relationship between the tangential growth rate of the steps and solution supersaturation. The effect of pyrophosphate (K4P2O7) and Fe3+ on the growth of the thin surface layers was discussed. The formation of Chainlike distribution solution inclusions in rapid grown KDP crystals were found closely related to the mechanism of growth from the edges.ADP (NH4H2PO4) crystals were grown from traditional method and point seed rapid growth technique, respectively. Their homogeneity is analyzed by laser interferometry and X-ray topography. Growth boundaries between (100) and (101) faces are the most serious defects in ADP crystals. They greatly reduce the crystal homogeneity. Growth bands and inclusions are the most common defects that influence the homogeneity of ADP crystals. Trivalent metal impurity ions preferred to congregate at growth bands, and formed inclusions.Mixed crystals of Kx(NH4)1-xH2PO4 were grown onto point seeds in solution mixtures with different molar concentrations of KH2PO4 by the method of temperature reduction. It was found that transparent mixed crystals could only grow from seed only in mixed solutions with certain mixed ratio. In addition to Sector and seed boundaries, the lattice parameters difference between pyramid and prismatic sectors also played an important role in the formation of stress and cracks in mixed crystals grown onto point seeds. Chemical etching revealed there was microcracks with length of hundreds of microns in the mixed crystals, which easily spread and induced cracks when the mixed crystals were taken out of growth solutions.