Observation of concentration boundary layers around growing or dissolving KH2PO4 crystals in stagnant solutions

The solute concentration profiles around KH₂PO₄ crystals growing or dissoloving in stagnant aqueous solutions were studied by the schlieren method after Toepler. By this technique the thicknesses of concentration boundary layers around the crystals, formed by free convection of solution, were measured in dependence of crystal size and super (under) saturation. In the case of dissolution, theoretical estimation of the boundary layer thickness yielded a fair agreement with the observed value. For growth, the process is dominantly limited by surface kinetics, whereas volume diffusion plays a minor role.     

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)     

The catalytic effect of impurity. The effect of benzene, acetone, organic acids, iron, and chromium on growth of KH2PO4 and C8H5O4K crystals

The effect of benzene, acetone, acetic, formic, and oxalic acids, iron, and chromium on the growth kinetics of KH₂PO₄ and C₈H₅O₄ K crystal faces has been studied. It is found that low concentrations of organic impurities increase growth rates of some crystal faces (the so-called catalytic effect of impurity). This effect is rather weak in the case of organic acids, however, it is clearly seen in the presence of inorganic impurity (Fe³⁺). The analysis of two models of growth (dislocation-free and B + S) under the assumption that the main cause of the catalytic effect is a decrease in the step energy showed that the calculated and experimental data are consistent only under certain assumptions that should be additionally verified both theoretically and experimentally.     

Effect of pH value on the growth morphology of KH2PO4 crystal grown in defined crystallographic direction

KH₂PO₄ single crystals were grown in aqueous solution at different pH values by using “point seeds” with a defined crystallographic direction at 59 degree to the Z axis. Atomic Force Microscope (AFM) was applied to observe the surface morphology of (100) face. It was found that at the same supersaturation, the larger steps appeared at the lower pH value before appearance of 2D nucleus. We found that 2D nucleus was occurred at σ ≤ 0.04 when pH value is <2.8. The occurrence of 2D nucleus was caused by the decreasing step‐edge free energy with the decreasing of pH value in the growth solution. In this paper, we observed the morphologies of (100) faces of KDP crystals which grew in solutions with different pH values. 2D nucleuses appeared on the terrace of growth steps when pH value down to 2.8 and 3.2 at supersaturation of 0.04, while pH value down to 2.4, only 2D nucleation control the growth. Therefore, the pH value can change the growth mechanism of KDP crystals.     

Growth of 2-methyl-4-nitroaniline (MNA) crystals by the bridgman method

Organic single crystals of 2-methyl-4-nitroaniline (MNA) up to 3 mm in diameter and 20 mm in length have been successfully grown by the Bridgman method using the purified reagent by sublimation. The crystals are transparent and yellow in colour by controlling the growth conditions. In the spectra of yellow coloured crystals no absorption peak is observed until about 450 nm. Also, the crystals of MNA have the two cleavage planes (311 ) and (010).     

Growth and thermal studies on pure ADP,KDP and mixed K1‐x(NH4)xH2PO4 crystals

The investigations on the formation of mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP) i.e. potassium ammonium dihydrogen phosphate, K_1‐x(NH₄)_xH₂PO₄ have been presented in this paper. Pure and mixed crystals of ADP and KDP have been grown by slow evaporation technique from the supersaturated solution at an ambient temperature 26±1 °C for ammonium concentration x in the range 0.0 ≤ x ≤ 1.0 in the case of mixed crystals. Crystal compositions were determined by flame atomic absorption spectroscopy and chemical analysis. The results of the X‐ray analysis of the grown crystals are also reported. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the kinetic process of dehydration and the high temperature phase behaviour. DTA showed the distinct thermal events attributed to dehydration of ADP, KDP and K_1‐x(NH₄)_xH₂PO₄. The results of thermal analysis and chemical analysis are consistent with each other. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of K1‐x(NH4)xH2PO4 mixed crystals onto z‐cut point seeds

Mixed crystals of potassium dihydrogen phosphate and ammonium dihydrogen phosphate were grown onto point seeds by the method of temperature reduction. It was found that the regeneration process of z‐cut point seeds became more and more difficult with increasing KH₂PO₄ concentration in the solution mixture. The interior stress and cracking of the mixed crystals were analyzed by synchrotron X‐ray topography. Large numbers of stress stripes were found at the seed and sectors boundaries. The lattice parameters of the pyramid and prismatic sectors of the prepared mixed crystal were calculated according to the X‐ray diffraction patterns. With solution containing 8 mol % KH₂PO₄, the lattice volumes of the prismatic sector of the mixed crystal were 1.3% larger than that of the pyramid sector of the crystal. Chemical etching revealed microcracks with length of hundreds of microns in the mixed crystals, which tended to spread and led to crystal cracking. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In Situ Observation of Step Evolution on {100} Face of KH2PO4 Crystal in Solution by Atomic Force Microscopy (AFM)

In situ observation of the surface morphology of {100} face of Potassium Dihydrogen Phosphate (KDP) crystals growing in solution was made with the use of Atomic Force Microscope. The slight movement of the steps connected with regeneration of the crystal surface has been detected for very low supersaturation. The height of the elementary steps has been established.     

Stokes to anti-Stokes intensity ratio in Raman spectra of the soft mode in KH2PO4 near the phase transition temperature

We investigate the Stokes to anti-Stokes intensity ratio for the Raman spectrum of a central peak in a potassium dihydrogen phosphate (KDP) crystal. The ratio deviates from the Boltzmann factor as the temperature approaches the phase transition temperature. The response functions evaluated by three ways assuming the fluctuation–dissipation theorem do not agree in a frequency region below ～30 cm^?1. This means that the usual relation based on the fluctuation–dissipation theorem are not directly applicable to the spectral analysis of the soft mode. Further, we compare the result of KDP with that of the cooperative rotational dynamics in liquid carbon disulfide.     

Nucleation of struvite (MgNH4PO4 · 6 H2O) single crystals and aggregates

The conditions (concentration and pH) for preparation of single crystals of struvite at 25 °C from ammoniacal solutions equimolar with respect to magnesium and phosphate ions are given. The limits are found above which crystal aggregates (twins or dendrites) precipitate as dominant morphology. The mechanisms of nucleation are discussed and the interfacial tension between crystals and solution is evaluated.     

Growth and characterization of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals with dimensions up to 20 mm × 15 mm × 15 mm have been successfully grown by using the top‐seeded solution growth technique and K₂W₂O₇ as solvent. Experiments show that this crystal is unstable in a strong acid or alkali environment and has a blue fluorescence emission. The density, hardness, melting point, absorption edge, transparency range, prominent Raman shift frequency are 7.57 g/cm³, 238 kg/mm², 800 °C, 380 nm, 400–5450 nm, 868 cm^–1 respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of semi organic nonlinear optical LHPCL crystals

The growth of single crystals of L‐histidinium perchlorate (LHPCL), a semi organic nonlinear optical material with dimension upto 5 × 6 × 2.5 mm³ is reported. Good optical quality single crystals were grown from aqueous solution by slow solvent evaporation technique. The grown crystals were characterized by single crystal X‐ray diffraction (XRD), FT‐IR and optical transmission studies. Thermal studies confirm that LHPCL has a fairly high thermal stability (272°C) when compared with other members of histidine family. The scanning electron microscopy (SEM) provides information on the quality of the samples and grain distribution over the surface of the sample. The dielectric constant and dielectric loss of the compound were measured at different frequencies, and also at varying temperatures and the results of these experiments are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of the organic nonlinear optical material mnba-Et (4′-nitrobenzylidene-3-ethylcarbonylamino-4-methoxyaniline) crystals by the czochralski method

For the first time melt growth of the nonlinear optical organic material 4′-nitrobenzylidene-3-ethylcarbonylamino-4-methoxyaniline (MNBA-Et) by the Czochralski (CZ) method has been carried out to achieve single crystals with large diameter. [100] oriented boules having a diameter of 15 mm and maximum height of 15 mm have been prepared. The structural quality of the CZ crystals is comparable to those from solution growth. The colour of the melt and the grown crystal changes from transparent to opaque as a result of using the same melt for multiple growing cycles deteriorating considerably the optical transmittance.     

Piezoelectric and Elastic Properties of Orthorhombic LiH2PO3 and LiH2PO4

Single crystals of LiH₂PO₃ and LiH₂PO₄, both of space group symmetry Pna2₁, with dimensions up to 40 mm were grown from aqueous solutions by controlled evaporation. Pyroelectric, dielectric, piezoelectric, elastic and thermoelastic properties were studied by standard methods. The static piezoelectric constants d₃₃₃ exceed d₁₁₁ of α-quartz by only a factor 2. The pyroectric effects reach 3 times and 7 times, respectively, that of tourmaline. The mean elastic stiffness of the phosphite is 13% smaller than that of the phosphate, a phenomenon also observed in the corresponding sodium and potassium salts.     

Growth and characteristics of HgGaInS4 single crystals

Single crystals of the HgGaInS₄ layered compound were grown by the iodine transport technique. Results of their optical, photoelectric, and radiative properties' study are presented. The band gap and the binding energy of holes on the sensitizing centres were determined to be E_g = 2.41 eV and E_a = 0.2 eV, respectively. A presence of quasi-continuously distributed states was stated which are responsible for the exponential segment of the absorption edge and which take part in the radiative recombination.     

Ca(H2PO4)2-H3PO4-K2SO4体系中石膏晶型及形貌调控

为将Ca(H₂PO₄)₂制备KH₂PO₄过程中的石膏资源化利用,以H₃PO₄与CaCO₃反应制备Ca(H₂PO₄)₂溶液,并与K₂SO₄溶液反应,进行Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌调控研究。结果表明:通过改变反应时间、反应温度、SO^2-₄过量系数和CaO含量等参数可对Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌进行调控,制得短柱状α-CaSO₄·0.5H₂O。体系在温度高于95 ℃和CaO含量为3.0%~5.0%(质量分数,下同)时形成α-CaSO₄·0.5H₂O,在CaO含量为5.5%主要形成CaSO₄·2H₂O;反应时间长于20 min和SO^2-₄过量系数大于1.4将形成K₂SO₄(CaSO₄)₅·H₂O,导致石膏晶体表面缺陷增加。本实验条件下,适宜反应条件为:反应时间10 min、反应温度95 ℃、SO^2-₄过量系数1.2和CaO含量5.0%,此条件下可制得长度42~70 μm、直径13~24 μm的短柱状α-CaSO₄·0.5H₂O,其抗折和抗压强度分别可达5.61 MPa和33.74 MPa,滤液中钾收率和脱钙率分别可达94.23%和83.80%。     

Growth,intensity and probabilities of f-f transitions of Nd3+ ions in KNd(PO3)4 single crystals

From a study of the melting diagram KPO₃—KNdP₄O₁₂ optimum conditions are derived for the growth of KNd(PO₃)₄ single crystals by the flux method. The absorption spectrum of KNd(PO₃)₄ was measured between 320 and 1000 nm at room temperature. The three JUDD -OFELT parameters Ω_λ were determined by numcerical methods and compared to the data for NdP₅O₁₄. A correlation has been attempted between the Ω₂ parameter and the site symmetry of Nd³⁺ in Nd-containing laser crystals. The calculated fluorescence branching coefficients from the ⁴F_3/2 level are in good agreement with the epxerimental data.     

Growth of K(DxH1 − x )2PO4 single crystals from solutions in the K2O-P2O5-(D, H)2O system

Based on the analysis of the K₂O-P₂O₅-D₂O solubility phase diagram, the optimum conditions of KD₂PO₄ crystallization—the compositions of mother solutions and the temperature range of crystallization—in the KH₂PO₄-D₂O system have been determined. The technique of K(D_xH_{1 ? x} )₂PO₄ growth is developed. The DKDP single crystals with deuterium concentration up to 88 wt % are grown on DKDP seeds from KH₂PO₄ solutions in D₂O by the method of temperature decrease.     

Growth of CdSiP2 single crystals by self-seeding vertical Bridgman method

Using a high purity CdSiP₂ polycrystalline charge synthesized in a single-temperature zone furnace, a CdSiP₂ single crystal with dimensions of 8 mm in diameter and 40 mm in length was successfully grown by the vertical Bridgman method. The quality of the crystal was characterized by high resolution X-ray diffraction and the full width at half maximum (FWHM) of the rocking curve for the (200) face is 33″. Thermal property measurements show that: the mean specific heat of CdSiP₂ between 300 and 773 K is 0.476 J g^?1 K^?1; the thermal conductivity of the crystal along the a- and c-axes is 13.6 W m^?1 K^?1 and 13.7 W m^?1 K^?1 at 295 K, respectively; and the thermal expansion coefficient measured along the a- and c-axes is 8.4×10^?6 K^?1 and ?2.4×10^?6 K^?1, respectively. The optical transparency range of the crystal is 578–10,000 nm, and there is no absorption loss in the spectrum from 0.7 to 2.5 μm, as often exists with ZnGeP₂ crystals grown from the melt.