Distribution of metallic ions in a single KDP crystal grown from aqueous solution

A single KDP (potassium dihydrogen phosphate) crystal was grown in a supersaturated solution containing a metallic ion (Al³⁺, Fe³⁺, or Cr³⁺). The growth rate, morphology, and distribution of the metallic ions into the KDP crystal were measured as the ionic concentration and supersaturation in the solution changed. It was found that in the KDP crystal, Al³⁺ and Fe³⁺ were greatly concentrated, but Cr³⁺ was diluted. Complete expressions for the effect of metallic ions on all aspects of the growth of KDP crystal were suggested. The growth rates of (100) and (101) faces were well correlated by the empirical equation and resulted in good estimation of morphology. The distribution of metallic ions into KDP crystal was also correlated by the distribution model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

点状籽晶法生长KDP晶体中散射颗粒分布

在不同的溶液pH值条件下进行了点状籽晶法慢速和快速生长KDP晶体实验,发展了观察晶体中散射颗粒分布的激光层析技术,通过图像处理得到了KDP晶体内部(100)面完整的散射颗粒分部图,对不同生长速度、不同pH值条件下点状籽晶法生长的KDP晶体的散射颗粒分部做了对比.利用表面光学投影技术观察了晶体表面宏观形貌,并由此分析了不同生长条件下生长机制对散射颗粒分布的影响.测定了散射颗粒密度不同部位的晶体透过率.     

Improvement of growth habit and optical properties of rapidly grown KDP crystal by adding diethylene triamine pentacetate acid in growth solution

By altering the concentration of a new additive ‐ diethylene triamine pentacetate acid (DTPA) in the growth solution, a series of KDP crystals were obtained by the “point seed” rapid growth method. The growth rates up to about 20 mm/day. Effects of DTPA on the growth habit and optical properties of these as‐grown KDP crystals were investigated. The results reveal that, with the increase of DTPA concentration in growth solution, the contents of impurity metal ions incorporated into crystal and aspect ratio of crystal morphology were both decreased gradually, while the UV transmittance of crystal was enhanced continually. In the presence of moderate concentration of DTPA (100–200 ppm), the solution stability was increased and optical properties of crystal (including optical homogeneity, light scattering and laser damage threshold) were all improved. However excessive doping (>500 ppm) has opposite effects. The impact mechanism was also analyzed combining with the structure of KDP crystal and chemical characteristics of DTPA molecular.     

Microscopic investigations of morphological structures on the pyramidal faces of KDP and DKDP single crystals

Studying a number of {101} faces of KDP and DKDP single crystals in the as-grown state we found in most cases one, rarely few, clearly stepped growth hillocks covering the whole face. The geometry of these growth hillocks was determined from photomicrographs; the step heights were measured with a profilometer. To prove our results we carried out X-ray topographic investigations and in-situ observations on KDP crystals. In addition we studied the as-grown faces of ADP and LiJO₃ single crystals.     

On the morphological instability of the growing crystals (IV). The effect of supersaturation inhomogeneity upon the morphological stability of KDP single crystals

The diffusion-induced inhomogeneity in the supersaturation on close packed faces of KDP crystals, growing from aqueous solutions has been investigated. The interferometrically found values of the concentration difference on the crystal edge and in the centre of the most closely packed face {100} were compared with the theoretically expected concentration nonhomogeneities calculated by means of CHERNOV 's formula. The comparison has been performed especially for the moment when the KDP crystals lose the stability of their polyhedral shape and gradually acquire a skeletal form. A fairly good coincidence was found.     

KDP晶体生长过程中溶液稳定性的研究

在KDP晶体生长过程中,溶液的稳定性对KDP晶体的光学质量影响较大.溶液的稳定性是多种因素共同作用的结果.本文主要研究了过饱和KDP溶液中晶胚的分布情况、降温过程中晶体生长驱动力与降温速度之间的关系,并分析了KDP晶体实际生长过程中影响溶液稳定性的主要因素.我们认为,通过改善KDP晶体生长过程中溶液的稳定性,并与其它措施和技术相结合,是提高KDP晶体光学质量的有效途径.     

Na+对KDP晶体生长的影响

本文利用传统的降温法和"点籽晶"快速生长法在不同Na+掺杂浓度的溶液中生长KDP晶体,定量研究了Na+对KDP晶体生长的影响.实验发现:Na+的存在降低了溶液的稳定性,致使KDP晶体柱面容易扩展.Na+的存在对KDP晶体的光学性能基本没有影响.     

Promotion of crystal growth rate in aqueous solution by direct contact with gas corona discharge

A new technique to promote crystal growth in aqueous solution using gas plasma is proposed. In this method, short‐lived radical species produced in solution which is contacted with gas corona discharge play a role to increase chemical potential of inorganic solute. In an experimental examination, single crystal of KDP was grown in a supersaturated solution which receives oxygen ions and radicals from adjacent corona discharge in air. KDP crystal has two unique growth faces (100) and (101), and the growth rates of both faces were increased considerably by generating the corona discharge. The both growth rates with and without corona discharge were well converged by one function based on chemical potential supersaturation. This result revealed that the solution in contact with gas corona discharge has a larger capacity of chemical potential than that without the discharge. Short‐lived species induced by gas corona discharge are considered to be anti‐solvents to cause this effect. The crystal growth process proposed here is considered to be an excellent method in terms of low impurity inclusion because such short‐lived species do not remain in the final crystal products and solution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rapid growth of KDP crystals in the coniform bottom device and their characterization

The coniform bottom device was designed and used in the rapid growth process of KDP crystal. A seed support rack was also designed to be used in rapid growth of KDP crystal to avoid spontaneous nucleation on the interface of seed crystal and rack. The KDP crystals were fast grown at the growth rate of up to 25 mm/day. The optical scatter centers in KDP crystals were observed and their transmissions of different parts were measured. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

点籽晶法快速生长中等口径KDP单晶及其性能表征

本文使用德国MERCK公司生产的KDP原料和自行研制的晶体快速生长装置,采用"点籽晶"快速生长法成功生长出了150 mm级中等口径的KDP单晶,晶体生长速度达到20 mm/d.晶体生长过程中,生长溶液稳定,没有杂晶出现,生长的晶体完好且透明.X射线粉末衍射和摇摆曲线分析表明晶体有着较好的结构完整性;同时,测试了晶体的透过光谱和光损伤阈值,发现快速生长的晶体有着较好的光学性能.     

Growth and properties of Ba‐doped KDP crystals

KDP crystals were rapidly grown from solution doped with different Ba²⁺ concentrations. The effects of Ba²⁺ on the growth rate, morphology and quality of KDP crystals were discussed. Significant changes in shapes and volume of the grown crystals have been observed. During the growth process, defect region expands gradually with the increasing Ba²⁺ concentration. Samples were cut from different parts of the as‐grown crystals for investigating the optical quality, including transmission spectrum, scattering centers. Through comparison, it is found that the nonuniform distribution of Ba²⁺ ions causes remarkable difference in optical quality between prismatic and pyramidal sectors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurement of three‐dimensional concentration gradients around a crystal growing from its aqueous solution using laser schlieren

Schlieren measurements of the gradients of the concentration field around a KDP crystal growing from its aqueous solution are reported. The measurement of the concentration gradient field is important for crystal growth because it controls the rate of solute transport from the bulk of the solution to the crystal surface. In the crystal vicinity, the concentration gradients have a three dimensional distribution. The concentration gradient field has been imaged using monochrome schlieren technique. Four view angles, namely 0, 45, 90 and 135° have been utilized. By interpreting the schlieren images as projection data of solute concentration gradient, the three‐dimensional concentration gradient field around the crystal has been determined using an algebraic reconstruction technique. At low supersaturation levels, the growth process is accompanied by weak fluid movement during which diffusion effects are significant. At higher levels of supersaturation and large crystal size, a well‐defined convective plume around the growing crystal is observed. Reconstruction of concentration gradients around the crystal explains the preferential growth rates of various faces of the crystal. The non‐circular shape of the crystal is seen to affect the symmetry of the distribution of concentration gradients in its vicinity. The effect of crystal morphology on the orientation of convection currents rising from the crystal surface has also been brought out on the basis of the reconstructed concentration gradients distribution in the growth chamber. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

快速生长KDP晶体表面的光学显微实时观察

设计了一套溶液降温法晶体生长显微实时观察装置,对快速生长KDP晶体{101}和{100}表面形貌的演化过程进行了实时观测分析.测量了晶体表面生长层切向生长速度随溶液过饱和度的变化曲线,并利用台阶生长动力学方程计算了相关动力学参数.进行了Fe3+掺杂实验,结果表明Fe3+的存在会影响到不同晶面上生长层的动力学系数,从而改变KDP晶体表面生长层的切向生长速度.     

Study on rapid growth of KH2PO4 and its characterization

Large size crystals of KH₂PO₄ (KDP) were grown by adopting rapid growth technique from point seeds in a 1500‐liter crystallizer which is used to grow KDP crystals by conventional method. The grown KDP crystal size can reach to 310 × 310 × 320 mm³ and the average growth rate was 8mm/day. The optic properties of the rapidly grown KDP crystals were characterized comparing with the KDP crystals grown by the traditional temperature reduction method. We found it that the optical quality of the KDP crystals we grown rapidly are not significantly different from those of KDP crystals grown by traditional method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of anions on rapid growth and growth habit of KDP crystals

The synthesis of KDP from its raw material has been found exist in the growth solution. In the crystal growth experiment, significant extension of specific faces was observed at low dopant concentration. At high doping concentration, the growth rate of the whole crystal decreased with no significant habit modification. The inhibiting effects of phosphite and other H-bonding anionic ions on the growth of pyramidal faces are discussed. Rapid growth rate experiments have been carried out with purified material and an averaged growth rate of 18.6mm/day was obtained.     

Chemical bond analysis of the crystal growth of KDP and ADP

The bond valence model is employed to calculate the bond strength of constituent chemical bonds formed between growth units in both potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) crystals, with the aim to predict and control the crystal shape. After calculating and comparing the relative growth rates of all selected planes, which are related to the crystallographic structure and chemical bond strength, the natural morphology of both KDP and ADP can be conveniently deduced. To check the calculated results, the crystallites of KDP and ADP are grown under different growth conditions; their morphologies accord well with our theoretical calculations. Meanwhile, the influence of ethanol anti-solvent on crystal morphology is microscopically interpreted, which alters the crystal morphology by changing the supersaturation of the growing solution and influencing the bonding process. When ethanol is added into the growing solution, the crystal shape becomes slender.     

Influence of La3+ ions on growth and NLO properties of KDP single crystals

Single crystals of pure and Lanthanum added KDP crystals were grown from aqueous solution. The influence of La³⁺ ions in KDP crystals is studied. Isolated centers are formed by La³⁺ ions in KDP structure along (100) plane. La³⁺ ions incorporated into superficial crystal growth layer and slightly affect the growth process as they generate weak lattice stresses. The creation of these weak lattice stress is confirmed by Vickers's micro hardness test. The HRXRD analysis showed reduced structural defects in the La added KDP in the (100) plane than pure KDP. The incorporation of La in the crystal was confirmed by EDAX analysis. The Kurtz's powder SHG efficiency was found to be 1.5 times that of pure KDP. The UV‐Vis transmission spectra of La added KDP showed excellent transmittance from 1100 nm to 340 nm and did not show any change in lower cutoff wavelength with respect to pure KDP. Laser damage threshold value has been determined using Q‐switched Nd:YAG laser operating at 1064 nm and with 65 ns pulses in single shot mode. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of KDP crystals from solutions with mechanical impurities

Growth of KDP crystals from aqueous solutions with SiO₂ particles whose size ranges from 10^–2 to 400 μm in the static and dynamic modes has been studied. The effect of mother-solution supersaturation and particle size and concentration on the process of particle capture by a growing crystal is considered as well as types of inhomogeneities formed in the crystal under the influence of these factors. It is shown that the larger the particle size, the higher the probability of particle capture by a crystal. The influence of supersaturation, growth rate, face morphology, and particle concentration on particle capture and defect formation in crystals is also discussed.     

Growth Kinetics of Potassium-Dihydrogen Phosphate Crystals in Solution

Growth rate data of (101) faces of KDP crystals as a function of the relative supersaturation of the solution are analyzed on the basis of BURTON , CABRERA and FRANK surface-diffusion model applied to the growth from solution. The characteristic constants in the BCF function are determined for 50°C. Approximate values of the free activation energies for dehydration, desorption, surface diffusion and entering the kinks from the surface are calculated. The experimental data previously obtained by MULLIN and AMATAVIVADHANA and by BELOUET are also discussed.     

Peculiarities of the growth of KDP single crystals with incorporated aluminium oxyhydroxide nanoparticles

Grown for the first time are KH₂PO₄ (KDP) crystals with incorporated aluminium oxyhydroxide Al₂O₃·nH₂O nanoparticles (n=3.5–3.6). The influence of the nanoparticles on the structure perfection and the growth kinetics of the crystal faces are studied. The presence of the nanoparticles in the crystal matrix is confirmed by the results of chemical analysis, X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The most essential inhibiting effect of the nanoparticles is observed for the {100} faces. The mechanism of influence of the nanoparticles on the {100} faces growth is explained on the base of the Cabrera–Vermilyea (C–V) model using Langmuir adsorption isotherm.