快速生长KDP晶体中的包裹体

利用底部热能输入晶体生长装置进行了KDP晶体快速生长,晶体生长速度达25mm/d.利用激光透射成像法、断面显微观察、SEM及电子能谱对快速生长晶体中的各种包裹体进行了观察,分别观察到了平行于生长面的层状包裹及其分布、线形排列的液相包裹以及微观包裹体的形貌、尺度和分布等,讨论了快速生长KDP晶体中包裹体出现的条件,分析了这些包裹体形成的原因.     

硫酸盐掺杂导致KDP晶体开裂的研究

采用传统降温法生长了掺杂不同浓度的SO42-离子KDP晶体,研究分析了晶体的宏观缺陷及开裂形式,从晶体生长角度初步分析了硫酸盐掺杂导致KDP晶体开裂的主要原因。实验表明,随着SO42-离子掺杂浓度的增大,KDP晶体的主要开裂形式是垂直于生长层{101}面的裂纹;晶体中裂纹存在的区域都分布有大量层层平行于生长层的母液包藏。随着SO42-离子掺杂浓度的进一步增大,晶体内包藏呈云雾状分布,裂纹不规则,晶体质量严重下降,透明度降低。     

大尺寸KDP晶体出槽力学效应数值模拟分析研究

大尺寸KDP（磷酸二氢钾,KH2PO4）晶体在出槽的过程中经常发生开裂现象,造成了较大的经济损失。为了研究大尺寸KDP晶体出槽过程中开裂机制并提出相应的防裂措施,采用有限元方法模拟了大尺寸KDP晶体的出槽过程,计算得到了KDP晶体出槽过程中晶体应力场的变化规律,结果显示降温冷却使晶体内部最大应力增大了100倍以上,而力学边界的变化使晶体最大应力增大的幅度较小,数据表明温度降低造成的应力集中是引起晶体开裂的主要原因。该结论的发现为提出相应的晶体防裂措施提供了重要的理论基础。     

KDP/KD*P晶体生长过程中柱面扩展的研究

目前在KDP/KD*P晶体的实际生长过程中,仍以传统降温法为主.在传统降温速度的基础上适当提高降温速度,可以加快KDP/KD*P晶体的生长速度,但与此同时有可能产生柱面扩展.为此,我们对不同生长环境下的KDP/KD*P晶体生长过程中柱面扩展进行了一系列研究.实验中所用KDP原料和去离子水均与生长大口径KDP晶体相同,其它各项条件也尽量模拟大口径KDP晶体生长过程中的实际情况.在晶体生长实验过程中通过研究不同条件下KDP/KD*P晶体的柱面扩展情况来研究柱面扩展对KDP/KD*P晶体光学质量影响的共同特点.通过分析和研究实验数据及晶体生长过程,我们认为在正常生长条件下引起柱面扩展的主要因素有两个溶液的过饱和度和籽晶柱面存在的缺陷.扩展部分的晶体的光学质量与本体部分差别较大,扩展部分对光的透过率在紫外部分下降很快,明显低于本体部分在这一波段的透过率.本体部分和扩展部分对光的透过率在其它波段差别不十分突出.     

SAPMAC法长蓝宝石晶体的温场设计、工艺分析与控制

采用SAPMAC法, 以a向为结晶取向, 生长出φ 240mm ×210mm, 重27.5kg的完整透明的蓝宝石单晶. 从理论上探讨了缺陷密度及晶体开裂与温度分布、生长速率、冷却速率等晶体生长工艺参数之间的关系. 设计了SAPMAC法生长大尺寸晶体的最佳温场分布、 工艺控制. 利用专用设备加工出大尺寸晶棒、板状窗口, 并测试了标准样品的红外透过性能.     

KDP晶体柱面生长速率实时测量研究

KDP晶体生长速率高精度地实时测量有助于研究各种因素对晶体生长的影响. 本文用激光偏振干涉法实现了对KDP晶体柱面生长速率和死区的实时测量, 精度达到0.01μm/min. 籽晶 尺寸等实验条件影响测量的结果, 小尺寸(约2mm×2mm)的晶体更有利于死区的表征, 溶解阶段造成的晶体表面位错坑是出现干扰测量的“异常”现象的根源.     

硫酸盐掺杂对KDP晶体生长的影响

SO2-4是KDP原料中一种常见的杂质离子,通过传统降温法和“点籽晶”快速生长法研究了掺杂K2SO4的KDP晶体的生长.实验表明,硫酸根低浓度掺杂时可提高溶液的稳定性,促进晶体的生长,造成柱面扩展;高浓度时溶液稳定性遭到破坏,出现杂晶,晶体生长速度变慢,晶体出现开裂,柱面发生“楔化”.     

泡生法生长掺碳钛宝石激光晶体的研究

钛宝石激光晶体在现代高功率激光领域具有重要的应用价值, 但大尺寸、高品质的晶体生长仍是当前钛宝石应用面临的重大难题. 本文研究了泡生法技术生长大尺寸掺碳钛宝石激光晶体, 结果显示, 泡生法生长得到的直径180 mm、30 kg的钛宝石没有出现应力集中的开裂等宏观缺陷现象, 钛离子在晶体中分布均匀接近理论值, 晶体的FOM值达到200. 该研究对低红外残余吸收, 高品质因素、大尺寸钛宝石激光晶体的生长应用具有重要的现实意义.     

DCTA对KDP晶体的快速生长与光学性能的影响

环己二胺四乙酸(DCTA)作为一种新型添加剂被加入到KDP晶体生长溶液中。采用“点籽晶”快速生长技术, 在掺杂100×10^-6 DCTA的饱和溶液中, 生长了KDP晶体, 生长速度达20 mm/d。研究了这种新型添加剂DCTA对快速生长的KDP晶体的生长习性和光学质量的影响, 并与常用添加剂EDTA的影响效果进行了对比。研究发现, 在KDP晶体生长溶液中添加100×10^-6 DCTA使生长溶液的亚稳区宽度提高了约10℃, 晶体(100)面的生长速度提高了3~10倍; 生长出的晶体在紫外波段的透过率上升了2~8倍, 晶体内部的光散射大大减轻, 激光损伤阈值也有所提高。添加剂DCTA对KDP晶体生长及性能的改善作用比同等浓度的EDTA更加显著。     

喷流转晶法KDP晶体生长系统的流动与传质模拟

提出了一种通过锥顶喷流改善KDP锥面过饱和度的晶体生长方法。采用有限体积法和滑移网格技术,对传统转晶法及喷流转晶法的KDP晶体生长过程进行了数值模拟。展示了两种生长方式下晶体表面过饱和度时均分布云图及均方差,分析了不同转速、不同喷流速度、不同晶体尺寸对晶面时均过饱和度及均方差的影响。结果表明:相比于传统转晶法,喷流转晶法晶体的锥面过饱和度提高且表面均匀性增加。提高喷流速度可以进一步提高锥面过饱和度,但其均方差却呈现先减小后增大的变化。旋转速度的增加能提高锥面过饱和度并减小其均方差。此外,晶体尺寸也会在一定程度上影响喷流的效果。     

Investigation into the room temperature creep-deformation of potassium dihydrogen phosphate crystals using nanoindentation

It has been a tremendous challenge to manufacture damage-free and smooth surfaces of potassium dihydrogen phosphate (KDP) crystals to meet the requirements of high-energy laser systems. The intrinsic issue is whether a KDP crystal can be plastically deformed so that the material can be removed in a ductile mode during the machining of KDP. This study investigates the room temperature creep-deformation of KDP crystals with the aid of nanoindentation. A stress analysis was carried out to identify the creep mechanism. The results showed that KDP crystals could be plastically deformed at the nanoscale. Dislocation motion is responsible for creep-deformation. Both creep rate and creep depth decrease with decrease in peak force and loading rate. Dislocation nucleation and propagation bring about pop-ins in the loaddisplacement curves during nanoindentation.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0234-9     

Elastic-plastic-brittle transitions of potassium dihydrogen phosphate crystals: characterization by nanoindentation

Potassium dihydrogen phosphate (KDP) crystals are widely used in laser ignition facilities as optical switching and frequency conversion components. These crystals are soft, brittle, and sensitive to external conditions (e.g., humidity, temperature, and applied stress). Hence, conventional characterization methods, such as transmission electron microscopy, cannot be used to study the mechanisms of material deformation. Nevertheless, understanding the mechanism of plastic-brittle transition in KDP crystals is important to prevent the fracture damage during the machining process. This study explores the plastic deformation and brittle fracture mechanisms of KDP crystals through nanoindentation experiments and theoretical calculations. The results show that dislocation nucleation and propagation are the main mechanisms of plastic deformation in KDP crystals, and dislocation pileup leads to brittle fracture during nanoindentation. Nanoindentation experiments using various indenters indicate that the external stress fields influence the plastic deformation of KDP crystals, and plastic deformation and brittle fracture are related to the material’s anisotropy. However, the effect of loading rate on the KDP crystal deformation is practically negligible. The results of this research provide important information on reducing machining-induced damage and further improving the optical performance of KDP crystal components.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00320-3     

Atomistic simulations of fatigue crack growth and the associated fatigue crack tip stress evolution in magnesium single crystals

Using Large-scale Atomic Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, atomistic simulations were performed to investigate the fatigue crack growth rate and the evolution of the associated atomic stress fields near the crack tip during fatigue crack growth in magnesium single crystals. The interatomic bonds of atoms were described using the EAM potential. The specimens with initial edge cracks were subjected to uniaxial Mode I cyclic loading. For the sake of revealing the influence of the initial cracks’ crystal orientations, three different orientations were considered. The fatigue growth rate can be expressed by da/dN = cCTOD, where the values of constant c are determined by the atomistic simulations. Notably, the values of the constant c are much larger for magnesium single crystals than for FCC single crystals and vary widely from one orientation to another. The simulation results show that the evolution of atomic stress fields was highly dependent on the crystal orientations due to anisotropy and magnesium single crystals’ HCP structure. Interestingly, the von Mises stress or normal stress around the crack tip controlled the fatigue crack growth behaviors.     

A study of the growth and growth mechanism of potassium dihydrogen orthophosphate crystals from aqueous solution

Observations made during the growth of potassium dihydrogen orthophosphate (KDP) crystals from aqueous solution are recorded. A model of the growth process is given which attempts to explain the origin of the features observed.     

Optical, structural and electrical properties of pure and urea doped KDP crystals

Single crystals of good optical quality, made of potassium dihydrogen phosphate (KDP) doped with urea were grown by slow evaporation solution growth technique at a constant temperature of 35 °C. Optical absorption and dielectric properties were studied for pure and urea doped KDP crystals. Using powder XRD studies, crystalline nature of pure and urea doped KDP crystals was confirmed. AC conductivity was measured for the grown crystals. DC electrical conductivity and photoconductivity studies were carried out for pure and urea doped KDP crystals and the differences caused by the dopant were also discussed.     

Potassium dihydrogen phosphate doped with organic complexes of rare-earth metals

We have examined conditions for the crystal growth of KDP doped with rare-earth (Ce, Sm, Gd, Yb) complexes with alizarin complexone. The complexes have different effects on KDP crystal growth and are selectively incorporated into the growth sectors of the crystals, which can be rationalized in terms of their structure and charge. In going from KDP solutions to crystals, the absorption bands of both the free ligand and its complexes with the rare-earth metals (482–510 nm) shift insignificantly. In contrast, the luminescence spectra of the complexes and ligand experience a bathochromic shift. The Stokes shift of the complexes in crystals is three to four times greater than that in solutions. The luminescence bands are centered at 598–625 nm.     

KDP晶体超精密切削过程中等效应力和应变分析

为了深入研究刀具几何参数对KDP晶体超精密切削过程的影响,以及等效应力和应变产生的原因及变化规律,采用商用有限元软件(Marc)对KDP晶体的超精密切削过程进行了有限元仿真,建立了KDP晶体超精密切削加工中应力和应变预测模型.仿真结果表明,KDP晶体超精密加工过程中等效应力主要集中在第一和第二变形区,等效应变主要集中在第二和第三变形区.研究表明,本文所建立的等效应力和应变预测模型是有效的,有限元仿真值与预测值之间的误差可以控制在10%以内.     

Growth habit and transparency of sulphate doped KDP crystal

KDP crystals were grown from the aqueous solution with different concentrations of sulphate by both the traditional temperature-lowering method and the rapid growth method. Sulphate showed a great effect on the growth and the properties of KDP crystals. With the rise of the dopant concentration, many defects occur such as mother liquid inclusions, parasite crystals and cracks. When the dopant concentration of sulphate reaches a certain value, the ultraviolet transmittance of crystals decreases a lot compared with crystals at low dopant concentration.