Study On The Growth And Dislocation Distribution Of KDP Crystal Through A Frustum Platform

KDP crystal is a kind of excellent water-soluble nonlinear optical material,which is widely used in photoelectric modulation,inertial confinement fusion,laser frequency conversion and other fields.How to improve the growth process to accelerate the growth rate and improve the quality of crystals has always been a hotspot of crystal growth research.Defect detection is an important basis for judging the quality of crystals,and dislocations are closely related to various defects in crystals.Through the detection of dislocation distribution,we could know the quality of crystal growth more accurately,and take measures to reduce the generation of defects.KDP crystal with size of 40-50 mm was grown by combining pyramidal seed and frustum platform,and compared with the crystal grown by flat platform.The formation rule of the pyramidal seed dislocation and the distribution of the dislocations in the crystal grown by the frustum platform and the flat platform have been studied.The crystal quality was tested by the rocking curve and microhardness test.The main contents of this paper are as follows:(1)There are hollow tubes and chain inclusions at the edge of the seed,with the average diameters of 100 μ m and 60 μ m,respectively.The formation of inclusions is related to the dissolution of the seed crystal before growth.The distribution of dislocations from the seed crystal is consistent with the formation region of inclusions,which are distributed in a triangle shape within a certain range.The angle between the main direction of the dislocation and the [100] direction is about 46 °.The formation of seed dislocation is affected by the recovery conditions.The dislocation etches and rocking curves show that the use of the frustum platform and relatively small initial supersaturation(1.5%)can help to reduce the formation of seed dislocation and improve the crystallization quality of the part of the crystal facing the seed.(2)The dislocation etches of(100)sections of crystals grown by the frustum platform and the flat platform indicates that the dislocation distribution in the upper half of the crystal grown by the frustum platform is similar to that of the crystal grown by the flat platform,and the dislocation density in some areas is lower than that of the crystal grown on the flat platform.For the lower half of the crystal grown on the frustum platform,there are few dislocation defects on the prismatic faces,and the dislocations are concentrated on the lower pyramidal surface that is in direct contact with the frustum.The existence of the lower pyramidal faces prevents the formation of new dislocations on the other faces and provides better growth conditions for the others.(3)The observation of the dislocation of the lower pyramidal faces in direct contact with the frustum shows that the crystal faces with a smaller angle to the slope of the frustum is helpful to terminate the dislocation on the frustum and reduce the retention of dislocations,at the same time,the growth striations are formed on the bottom surface of the crystal.Considering the orientation of dislocations,the inclination of the slope of the frustum should not exceed 40 ° to reduce the retention of dislocations during the growth process.(4)Hardness analysis shows that the use of the frustum platform improves the crystalline perfection of the prismatic faces partly.Combining appropriate supersaturation and rotation speed,the crystal quality of the crystal grown on the frustum platform could be further improved.