溶液法五氯硝基苯单晶生长的研究

测定PCNB在丙酮溶剂中的溶解度,采用恒温溶剂蒸发法首次在丙酮中成功生长出PCNB单晶.结果显示:302 K以下温区具有较小的温度系数,适用于恒温蒸发法生长单晶;生长出了厘米尺寸的PCNB晶体;红外和拉曼光谱的测量结果说明所生长的晶体中未包裹溶剂;X射线衍射分析表明,所生长出晶体结构为六方晶系,单晶质量较好.     

Growth of (CH3)2NH2CuCl3 single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of low-dimensional magnet (CH₃)₂NH₂CuCl₃ (DMACuCl₃ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility.     

Growth, morphological, mechanical and dielectric studies of semi organic NLO single crystal: l-argininium perchlorate

Optically good quality single crystal of l-argininium perchlorate (abbreviated as LARPCL), a promising analog of LAP was successfully grown by slow solvent evaporation technique at room temperature. The unit cell parameters and the morphology of LARPCL single crystals were determined by single crystal XRD. The Vickers microhardness measurements were carried out on the grown crystals to estimate the mechanical properties. The dielectric constant and dielectric loss of the crystal were measured as a function of frequency and temperature, and the results are discussed.     

Single crystal growth of copper phthalocyanine using exaltation–evaporation growth method

A new method of growing single crystal for β-form copper phthalocyanine (CuPc) is presented in this paper. Melted anthracene was used as solvent of CuPc. The method, vaporizing the solvent using an automatic exaltation machine, was employed to grow CuPc single crystals. The needle-like single crystals of CuPc up to 11.6 mm in length were obtained by applying this method. The influences of different temperatures, exaltation speeds and concentrations on the single crystals growth were also discussed. The method was called exaltation–evaporation growth method.     

Synthesis, growth and characterization of Bis S-benzylisothiouronium tetrachlorido zincate (II) a semiorganic nonlinear optical crystal

A new semiorganic nonlinear optical (NLO) crystal, Bis S-benzylisothiouronium tetrachloridozincate (II) (SBTTZ), has been synthesized and good optical quality needle shaped single crystals of the title material were grown by solvent evaporation solution growth method at room temperature. Powder X-ray diffraction pattern confirms the crystallinity of the material. Single X-ray diffraction study was carried out to establish the existence of intermolecular hydrogen bonding in the crystal. The UV–Vis–NIR spectrum indicates that the crystal has very good transmittance in the entire visible and near IR regions of the spectrum suggesting the suitability of the material for NLO applications. The presence of various functional groups was confirmed by FT IR spectroscopic technique. The ¹H NMR spectrum confirms the molecular structure. The thermal and mechanical stabilities have been confirmed by TG/DTA analyses and Vickers microhardness study respectively. The SHG in the grown crystal was identified by modified Kurtz–Perry method using Nd:YAG laser as the source.     

Growth micromorphology of stearic acid crystals

Growth and micromorphology of stearic acid crystals grown by solvent evaporation method has been studied. The effect of the solvent and the rate of evaporation of the solvent on the growth micromorphology has been investigated. The formation of spherulitic growth features, rhombic platelets of B- and C forms having growth spirals associated with solution channels and twinned crystals involving B-B, C-C, and B-C forms is observed. The complexity of the twins involving the B- and C forms is discussed.     

Growth and characterisation of benzaldehyde semicarbazone (BSC) single crystals

Single crystals of potential organic nonlinear optical materials of Benzaldehyde Semicarbazone (BSC) were grown by slow evaporation technique. The grown crystals were identified by X-ray diffraction method. The functional groups were identified from FT-IR spectrum. UV-visible and thermal gravimetric analyses were made.     

GaN single crystals of different habit grown from solution at near atmospheric pressure

Near atmospheric pressure solution growth is one of the many developing methods for growing bulk GaN from solution. Apart from other approaches, this method holds certain advantages, such as relatively low growth pressure and temperature, and the ability to grow high quality GaN crystals with different orientations by varying the solvent composition. GaN whiskers of millimeter scale size with exceptional mechanical and optical properties were grown from solution. Crystals of near isotropic shape were also grown from solution by manipulating additives in the basic solvent.     

Growth and characterization of 2-amino-5-chlorobenzophenone (2A-5CB) single crystals

Organic nonlinear optical single crystals of 2-amino-5-chlorobenzophenone (2A-5CB) were grown in ethanol by slow solvent evaporation technique. The grown crystals were characterized by single-crystal XRD, FTIR, FT-Raman and UV–vis–NIR techniques. The UV–vis–NIR spectrum ascertains the cut-off wavelength of the sample as 390 nm. The powder second harmonic generation (SHG) technique reveals that 2A-5CB crystal has its SHG efficiency nearly three times that of KDP. The dielectric response of the sample was studied in the frequency region of 50 Hz–1 MHz at varying temperatures. The photoconductivity studies indicate that the 2A-5CB crystal exhibits negative photoconductivity. TGA–DTA studies confirm the melting point of the sample as 101.5 °C.     

Inversion domains and parallel growth in ammonothermally grown GaN crystals

Macro-defects such as twins, inversion domains, crevices, and columnar growth occasionally appear in ammonothermally grown GaN crystals. Twinning mechanisms and parallel growth are proposed to explain the formation of these defects. As a polar crystal with wurtzite structure, GaN can have several different kinds of twins depending on the polarity arrangement of each individual twin. Inversion domains are formed in one of the twinning mechanisms. Parallel growth is used to explain the formation of pits on the nitrogen face and the columnar growth on the gallium face. Etching in hot H₃PO₄ is used to reveal the polarities and defects of GaN crystals when they are indistinguishable. Optical microscopy, scanning electron microscope, and cathodoluminescence are also employed to study these defects. In addition, seed quality, avoidance of macro-defect formation, and impurity effects are also discussed.     

Morphology and characterization of ammonium bichromate crystals grown from aqueous solutions

The morphology of ammonium bichromate single crystals grown from aqueous solutions by solvent evaporation method at temperatures between 22 and 56 °C is investigated. It is found that the crystal morphology changes monotonically with an increase in growth temperature. Chemical etching is used to characterize the as-grown crystals.     

Vacancy defects in bulk ammonothermal GaN crystals

We have applied positron annihilation spectroscopy to study in-grown vacancy defects in bulk GaN crystals grown by the ammonothermal method. We observe a high concentration of Ga vacancy related defects in n-type samples in spite of the low growth temperature, suggesting that oxygen impurities promote the formation of vacancies also through other mechanisms than a mere reduction of thermodynamical formation enthalpy. On the other hand, no positron trapping at vacancy defects is observed in Mg-doped p-type samples, as expected when the Fermi level is close to the valence band and intrinsic defects are dominantly positively charged. Annealing of the samples at temperatures well above the growth temperature is found to change significantly the defect structure of the material.     

Synthesis, growth of organic nonlinear optical crystal: Semicarbazone of 2-amino-5-chloro-benzophenone (S2A5CB) and its characterisation

A new organic crystal of semicarbazone of 2–amino–5–chloro–benzophenone has been grown as a single crystal by slow evaporation solution growth technique for the first time in the literature. The grown crystal has been characterised by proton nuclear magnetic resonance spectral analysis and single crystal and powder X-ray diffraction studies. Functional groups of the crystallised molecules were confirmed by FT-IR and FT-Raman analyses. Mechanical strength of the crystals was studied by microhardness test. Optical transparency of the grown crystals has been studied by UV-Visible spectra. The second harmonic generation property of the compound was analysed.     

Extended defects in bulk GaN and III-nitrides grown on this substrate

A short review of the structural perfection of high-pressure grown bulk crystals is given. As-grown undoped and Mg-doped crystals are described. The dependence of defect arrangement and quality of the surface on growth polarity is described. A high perfection of homoepitaxial layers grown on these substrates is shown. However, growth of thick layers by HVPE may lead to the formation of differently arranged dislocations and the formation of low angle grain boundaries associated with cracks. It is shown that the introduction of dopant or growth of mismatched layers on undoped high-pressure substrates may lead to the formation of additional defects.     

Growth and characterization of organic nonlinear optical material: Benzilic acid

The organic nonlinear optical crystals of benzilic acid were grown by the slow evaporation method using ethanol as a solvent. Single-crystal X-ray diffraction (XRD), powder XRD studies and Fourier transform infrared (FTIR) spectral analysis were carried out to confirm the benzilic acid crystal. The optical transparency was studied by ultra violet (UV)–visible spectral analysis. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. The melting point of the grown crystal was confirmed by differential scanning calorimetry (DSC) analysis. The second harmonic generation (SHG) efficiency was found to be 2 times that of KDP.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

Unidirectional seeded single crystal growth from solution of benzophenone

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means of a seed fixed at the bottom of the ampoule. By selecting a suitable ring heater voltage and by controlling the ring heater voltage, nucleation and the growth rate of the crystal were controlled more effectively. By employing this novel method, benzophenone single crystal ingots of diameters 10 and 20 mm and length more than 50 mm were successfully grown using xylene as solvent. The ease in scaling up of diameter from 10 to 20 mm shows the vital advantage of this technique. It was possible to achieve solute–crystal conversion efficiency of 100 percent. The grown benzophenone crystal was characterized by FTIR, TG and DTA, powder X-ray diffraction, X-ray rocking curve, optical transmission study and powder SHG measurement. The results show that the crystal quality is at least as good as the quality of the crystal grown by other known methods. Also, microbial growth was naturally avoided in this method, as the fresh solution is constantly made available for the growing crystal.     

Growth and morphology of p-terphenyl single crystals

The results of a preliminary investigation of the growth and morphology of p-terphenyl crystals grown by sublimation and by solvent evaporation methods are reported. It was observed that lozenge–shaped (001) crystal plates are obtained from xylene and benzene solution while dendritic crystals by sublimation. Crystallographic orientation of the plates and microscopic observations of as-grown crystal surfaces are also described.     

Structural, thermal and dielectric studies on a new solution grown 4-dimethylaminopyridinium dihydrogen phosphate crystal

Single crystals of 4-dimethylaminopyridinium dihydrogen phosphate (DMAPDP) (C₇H₁₃N₂PO₄) were grown by the solvent evaporation method. The three-dimensional structure was solved by the single-crystal X-ray diffraction method which belongs to triclinic crystal system and the molecular arrangements in the crystal were studied. The thermal behaviour was investigated using differential scanning calorimetry (DSC) and no phase transition was identified in the temperature region −150 to 230 °C. The thermal parameters—thermal diffusivity (), thermal effusivity (e), thermal conductivity (K) and heat capacity (C_p) of DMAPDP were measured by an improved photopyroelectric technique at room temperature. Dielectric constant and dielectric loss of the grown crystal were evaluated for the frequency range 1–200 KHz in the temperature region 28–135 °C. The Vicker's hardness was measured as 42.2 for a load of 98.07 mN. The laser induced surface damage threshold of DMAPDP crystal was found to be 4.8 GW/cm² with nanosecond Nd:YAG laser.