X‐ray Topographic Characterization of L‐Arginine Phosphate Monohydrate Crystals

L‐arginine phosphate monohydrate (LAP) organic crystals were investigated by X‐ray Lang topography. Selected topographs of nearly perfect seeded grown and self‐nucleated crystals show that typical defects inside are grown‐in and post‐growth dislocations, growth sector boundaries, and microbes, while their features are presented and discussed. No structural defects associated to the presence of step bunching on the (100) surface of the crystal have been observed by X‐ray topography.     

KTP crystal growth from the starting materials reacted in solution

Using the solution‐reacted materials, potassium titanyl phosphate (KTiOPO₄, KTP) crystal was grown by the top‐seeded solution growth (TSSG) method. The solution‐reacted precursor was characterized by scanning electron microscope, and the solubility of KTP in K₈P₆O₁₉ was measured. The crystals were investigated by synchrotron radiation X‐ray topography, scattering centers measurement, weak absorption test and damage threshold test. The results showed that dispersion was better and solubility was higher than those by solid‐reacted method. Compared with the conventional crystal, KTP crystal grown from the solution‐reacted precursor had fewer defects, fewer scattering centers, lower weak absorption and higher damage threshold.     

Geometrical aspects of solid solution separation by evaporation‐condensation driven in a closed system by a small temperature difference

Evaporation‐condensation driven in a closed system by a small temperature difference has demonstrated its ability to deliver semiconducting IV‐VI and II‐VI solid solution crystals of highest compositional uniformity. Geometrical aspects of solution component distribution emerging in the crystals grown in the near equilibrium evaporation/condensation systems are considered in this paper. The conclusion is drawn that no increase in the range of compositional variations with increase in the crystal size is to be anticipated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

熔盐法和水热法KTP晶体的晶胞参数及拉曼光谱特征

利用X射线衍射和显微激光拉曼光谱研究熔盐法自发结晶的KTP晶体、顶部籽晶熔盐法KTP晶体和水热法KTP晶体的晶胞参数和拉曼光谱特征,分析和比较不同方法生长的KTP晶体的晶体结构与化学键特征峰.研究表明:KTP晶体的晶胞参数与晶体生长方法有关,熔盐法自发结晶的KTP晶体生长过程中降温速率较快,晶胞体积相对较小;熔盐法和水热法KTP晶体中部分拉曼特征峰的位置因生长方法不同呈现一定的差异,水热法KTP晶体在782 cm-1、744 cm-1和515 cm-1处出现的特征峰可视为水热法KTP晶体的标志峰,借此可将其与熔盐法晶体相区分.     

Investigation of structural perfection and faceting in highly Er‐doped Yb3Al5O12 crystals

The undoped Yb₃Al₅O₁₂ (YbAG) single crystals and doped with 1.5, 10 and 30 at% erbium were grown by the Czochralski method. The YbAG crystals offer efficient emission of laser beam of 2.94 µm and 1.55 µm important for practical applications in communication and medicine. The crystals were investigated by various synchrotron X‐ray diffraction methods including white beam topographic methods, monochromatic beam topography and recording of the rocking curves. The experiments were performed at E2 and F1 experimental stations in HASYLAB. The investigations proved a good crystallographic perfection of the crystals, in most cases revealing only segregation fringes and growth facets. The crystallographic identification of the facets was performed together with direct evaluation of growth front radius from the transmission section topographs. Relative lattice parameter changes connected with erbium segregation were found to be less than 2 × 10^‐5 inside the segregation fringes and 8 × 10^‐5 in the facets. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solution growth and comparative characterization of L‐HFB single crystals

Single crystals of L‐histidine tetrafluoroborate (C₆H₁₀N₃O₂BF_{4 ,} L‐HFB) were grown by solution growth method using two different temperature profiles: conventional, in which the growth temperature was kept constant at 30°C and rapid, in which it was increased in steps of 1 K per day while keeping the other growth conditions same. Crystals grew in nearly 30 and 10 days in the two methods, respectively. The crystals were transparent and showing its characteristic morphology. Both types of crystals were characterized by XRD for their structural comparison. Surface morphology and growth features of the crystals were studied by SEM. Features of two dimensional layer growth steps, rectangular etch pits, slip lines and bands, etc. were observed. The presence of various functional groups and their bonding were studied by FTIR in the range 4000‐400 cm^‐1. Thermal stability of the crystals was determined by thermo‐gravimetric and differential thermal analysis. The generation of green light due to second harmonic generation for fundamental λ =1064 nm has been confirmed in both cases. Dielectric constant measurement was carried out in the range 20Hz‐2MHz. In the UV‐Vis studies, high transmittance and a shorter ‘lower cut off' value (232 nm) were observed. The effect of rapid growth on the structural, morphological and optical properties of the crystals were studied and compared to those of crystals grown in conventional way. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison Study of Mixing Effect on Batch Cooling Crystallization of 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) Using Mechanical Stirrer and Ultrasound Irradiation

The insensitive explosive 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) has been recrystallized from water in an effort to prepare crystals with smaller size and narrower distribution in a batch cooling crystallizer. Two mixing devices, i.e., a mechanically stirred system with and without ultrasound in aqueous media were employed to compare the mixing effect on the crystallization. Under ultrasound irradiation, the metastable zone width was significantly reduced by more than 2 fold and the crystal size was shifted from 140∼160 μm to 50∼70 μm with a narrower CSD compared to the mechanically stirred system. However in the mechanical stirrer, the mixing effect on NTO crystallization was negligible if the impeller speed was sufficient to suspend all crystals in the crystallizer. It was found that the crystal growth was not influenced by mixing. We suggest that the NTO crystals were formed by primary heterogeneous nucleation that is common in batch cooling system. Finally, the population balance model (PBM), with the empirical nucleation and growth kinetic expressions, was solved numerically to predict the crystal size and the CSD with batch time, and the results were in good agreement with the experimental data.     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and structure of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals have been grown by the top‐seeded solution growth technique. Bulk crystal with dimensions up to several centimeters is obtained for the first time. Several self‐flux systems have been used for the growth from the solution and the experiments using K₂W₂O₇ as a solvent are detailed. Powder and single crystal X‐ray diffraction of this crystal are reported. The structure refinement shows that KBi(WO₄)₂ crystallizes in the monoclinic space group C2/c, with a=10.837(3), b=10.586(3), c=7.622(2)Å, β=130.860(3)°, V=661.4(3)ų, and Z=4. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Brittleness of protein crystals

A simple technique for studying the brittleness of small crystals is reported. The limits of fracture toughness of tetragonal hen‐egg white lysozyme crystals, oriented with their c‐axis normally to the substrate, were measured. The strong mechanics anisotropy of those crystals was confirmed. The role of the water present in the protein crystal lattice was re‐considered in seek for a more holistic understanding of the process, the idea being that the intra‐crystalline solution sustains the globular protein molecules in their native configuration. Also it is argued that this water may contribute for holding together the huge bio‐molecules in the crystal lattice (that is to act as additional “glue” in the crystal). The hypothesis is that dynamic chains of H‐bonds in the intra‐crystalline water are likely to be prolonged to connect protein‐to‐water‐to‐protein.     

Structure and optical properties of near stoichiometric Ce:LiNbO3 crystals

The near sotichiometric Ce:LiNbO₃ (Ce:SLN) crystals were grown by the top seeded solution growth (TSSG) method by adding K₂O flux to Li₂O‐Nb₂O₅ melt. Their UV‐vis absorption spectra and IR spectra were measured and discussed to investigate their defect structure. The results showed that the grown crystals were near stoichiometric and Ce ions in the crystals located the Li site. Photorefractive properties of Ce:SLN crystals were studied by two‐wave coupling experiment. The results of the two‐wave coupling experiments of the crystals showed that as the CeO₂ doping concentrations increased, the diffraction efficiency increased, photoconductivity decreased and the writing time and erasure time increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of sulphamic acid single crystals grown by Sanakaranarayanan‐Ramasamy (SR) method

By directional solidification, single crystal of Sulphamic acid (SA) was successfully grown from aqueous solution by Sankaranarayanan‐Ramasamy (SR) method. A vertically designed L‐bend was used to avoid the effect due to spurious nucleation. A vertical bottom‐seeded ampoule was used for the growth of single crystal. A seed crystal was mounted at the bottom of the ampoule. Sulphamic acid crystals of up to 40 mm in diameter and 60 mm in length have been grown with a growth up to 10 mm per day. The grown sulphamic acid single crystal was characterized using X‐ray powder diffraction analysis, Raman, FTIR, and optical transmission studies. The dielectric behaviour was measured in the frequency range of 1 kHz–10 MHz for the temperature ranges from 30 °C to 170 °C. The sulphamic acid single crystal was also grown by conventional method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,bulk growth,polarizability and nonlinear optical properties of γ‐glycine single crystals

The role of sodium acetate, sodium nitrate, sodium hydroxide and malonic acid as additives in assisting the nucleation of γ‐polymorph from solution has been investigated. For the first time large dimensional bulk single crystals of γ‐glycine have been grown at the optimized concentration of the additives by the top seeded slow cooling technique. The bulk growth of single crystals elucidates well the unidirectional growth characteristics and the existence of merohedral twinning in γ‐ glycine. Polarizability, plasmon energy and Fermi energy has been evaluated for the first time for γ‐glycine single crystals based on an analytical approach. Structural affirmation of the nucleated polymorph has been carried out by Powder x‐ray diffraction and the thermal characteristics of the nucleated polymorph are well revealed by Differential Scanning Calorimetry. The non linear optical characteristics of γ‐glycine studied by Kurtz and Perry technique revealed increased SHG efficiency with the highest of about 2.2 in the presence of malonic acid compared to the standard Potassium dihydrogen orthophosphate (KDP).     

Growth of TGS crystals using uniaxially solution‐crystallization method of Sankaranarayanan‐Ramasamy

The recently discovered crystal growth method called uniaxially solution‐crystallization method of Sankaranarayanan–Ramasamy (SR) is modified in some aspects and used for growth of triglycine sulphate (TGS) crystals. The modification leads to the simplicity, reduction of cost and avoided the temperature fluctuations. The 〈010〉 direction of TGS is very important and used for fabrication of infrared detectors. Using this method, the 〈001〉, 〈010〉 directional crystals of TGS were successfully grown in a glass crystallizer. The grown crystal was characterized by HRXRD, UV‐Visible and dielectric studies. The results prove the suitability of the modified SR method for oriented TGS crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental research of effects of different rotation radii on the growth rate of potassium dihydrogen phosphate crystals

Comparing with the traditional concentric rotation method (rotation radius is 0 cm), the effects of different rotation radii on the growth rate of KDP crystals were studied by experimental methods. It was found that with the increase of rotation radius from 0 cm, the growth rate of each direction of crystals first increased and then decreased in a size‐unchanged vessel. The smaller the distance between the crystal and vessel wall, the less the growth rate. This phenomenon was named the “wall collision effect”. Also, the value of growth rate reached a maximum when the rotation radius was about half of its allowable largest value in the size‐unchanged vessel. In addition, an increase of the rotation radius could improve the crystal growth rate under the same linear velocity of crystal movement. Finally, the uniformity of crystal growth has also been analyzed compared with the concentric rotation radius. It was found that the uniformity of crystal growth was best when the rotation radius was half of its allowable maximum value, and it was more conducive to the actual application of KDP crystals.     

Microscopic studies on imperfections in selected YAB single crystals

The as‐grown surface and inner structures of undoped and Nd³⁺‐, Cr³⁺‐, V³⁺‐, Ce³⁺‐, Er³⁺ and Yb³⁺ – and (Er³⁺ + Yb³⁺) – doped yttrium aluminum borate (YAB) single crystals grown from (K₂Mo₃O₁₀ + B₂O₃) flux by spontaneous crystallization or top seeded solution growth (TSSG) technique, were investigated using optical and scanning electron microscopic and analytic chemical methods. Fine and rough growth hillocks of dislocational origin, growth layers, traces of inner planar defects and foreign phase crystalline debris were found and analyzed on the as‐grown faces of crystals. Irregular grains and regular block structures and foreign phase inclusions were observed and studied in the interior of the crystals. The chemical compositions measured by energy dispersive X‐ray spectrometry on perfect and imperfect micro regions are compared with those obtained by flame atomic absorption spectrometry on bulk crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation on the regeneration of Z‐cut KDP crystals

The regeneration of Z‐cut KDP crystals is explored by analyzing the growth of thin surface layers formed. The structural defects and crystalline perfection of the thin surface layers are evaluated by white‐beam synchrotron radiation topography and high‐resolution X‐Ray diffraction respectively. It shows that the thin surface layers have the same crystal structure as KDP crystal. There are large numbers of defects in thin surface layers and the crystalline quality is very poor. The growth velocity of thin surface layers is firstly accurately measured by a newly‐designed in‐situ crystal growth observation setup. It is found that the growth velocity of the thin surface layers strongly depends on the flow rate of the growth solution. The hindering effect of pyrophosphate (K₄P₂O₇) on the growth of the thin surface layers is discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Habit modification and improvement in properties of potassium hydrogen phthalate (KAP) crystals doped with metal ions

Potassium hydrogen phthalate (KAP) single crystals were grown by slow evaporation and slow cooling techniques. The growth procedure like temperature cooling rate, evaporation rate, solution pH, concentration of the solute, supersaturation ratio etc., has been varied to have optically transparent crystals. Efforts were made to dope the KAP crystals with rubidium, sodium and lithium ions. The dopant concentration has been varied from 0.01 to 10 mole percent. Good quality single crystals were grown with different concentrations of dopants in the mother phase. Depending on the concentration of the dopants and the solution pH value, there is modification of habit. Rubidium ions very much improve the growth on the prismatic faces. The transparency of the crystals is improved with rubidium and sodium doping. The role of the dopants on the non‐linear optical performance of KAP indicates better efficiency for doped crystals. The grown crystals were characterized with XRD, FT‐IR, chemical etching, Vickers microhardness and SHG measurements. The influence of the dopants on the optical, chemical, structural, mechanical and other properties of the KAP crystals was analysed. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Separation of glucose and fructose by freezing crystallization

This work comprises the implementation of a methodology for the study of an industrial crystallization process by freezing and cooling to be applied in the separation of sugars with industrial relevance (glucose and fructose). The main interest is the production of fructose. This sugar is obtained by sucrose hydrolysis in acidic solutions, which yields an equimolar mixture of glucose and fructose. The developed separation process is based on the solubility difference between the sugars. Experiments were carried out in a jacketed glass crystallizer where the solution coming from the sucrose acid inversion was submitted to a slow cooling. Since glucose has lower solubility than fructose, it crystallizes in the bulk as the temperature is lowered, thus it can be removed from the solution by fliltration or centrifugation. Best fructose‐glucose separation was achieved for a total sugar concentration of 50 wt%. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical optimization of thermal field in CdTe crystal growth by travelling heater method

Cadmium telluride (CdTe) and his compounds play a leading role in X‐ray and γ‐ray detector technology. One of the most used methods for growing these crystals is the travelling heater method (THM). The ingots obtained by using this technique show excellent composition uniformity, but the structural quality is affected by the presence of large grains which appear because of large curvatures of the solid‐liquid interface during the solidification process. This numerical work investigate the thermal field and melt convection in CdTe processing by THM in order to elucidate the mechanism of growing these crystals. The influence of the furnace geometry on the interface shape and temperature gradient in liquid is analyzed for samples with small (1 cm) and large (5 cm) diameters. The computations include flow effects on thermal field in the melted zone. The thermal conditions are optimized for THM growth of CdTe crystals at high solidification temperatures. A new multi‐zone furnace configuration for growing crystals of large diameter and flattened interface is proposed in this work.