Phase transitions in melt-grown PbI2 crystals

Employing the method of zone- refining single crystals of PbI₂ of different purities were grown. Using X-ray diffraction technique their structure was found to be of the type 12R and in some cases 12R+4H. The crystals were re-examined after prolonged storage of several months at room temperature. Neither the crystals of very high purity nor of relatively less purity transformed. But thecrystals having intermediate purities did transform from 12R to 2H. This observation establishes a clear link between impurities and phase transitions. The results have been explained on the basis of nucleation and growth mechanism of stacking faults. Also it has been concluded that the presence of impurities is a must for the formation of polytypes.     

混合碱液法生长的氧化锌晶体表面形貌及光致发光性质

从NaOH和LiOH的混合碱液中生长了具有不同六方形貌的淡黄色ZnO晶体.采用X射线粉末衍射的方法对晶体的物相进行了分析,利用光学显微镜和扫描电镜对晶体的形貌进行了表征,同时利用电子探针能谱仪对晶体的组分进行了分析.从晶体的室温光致发光谱图中可以观测到380,445,512,652 nm处存在与晶体结构和缺陷相关的发射...     

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV–visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.     

Temperature controlled synthesis of SrCO3 nanorods via a facile solid-state decomposition rout starting from a novel inorganic precursor

Strontium carbonate nanorods have been successfully synthesized via solid-state decomposition of a new precursor, [Sr(Pht)(H₂O)₂]. The obtained nanorods were found to be orthorhombic with the length of 70-100 nm and the diameter of about 10-15 nm. The Effect of calcinations temperature on morphology and purity of the products has been investigated. Strontium carbonate nanorods were formed at 500 °C. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. In addition, further evidence for the purity and stoichiometry of the product was obtained by XPS (X-ray photoelectron spectroscopy) spectrum.     

Effect of tin-doping on polytypism of melt-grown crystals of cadmium iodide

The effect of doping of metallic tin in cadmium iodide crystals has been systematically studied. The method of zone melting has been employed both for purification and for the growth of single crystals of cadmium iodide. The doping has been carried out by zone levelling technique. The as-grown crystals have been characterized by X-ray diffraction and physical methods. All the crystals have been found to consist of the most common polytype 4H. Unlike the case of pure undoped crystals of cadmium iodide grown from melt, all the X-ray photographs showed the presence of arcing. None of the photographs showed the presence of streaking. Besides, the doped crystal were found to be harder than the crystals of undoped cadmium iodide. Unlike the undoped crystals, cleavage in the doped crystals was found to be difficult and highly localized. The results have been discussed.     

Analysis of dislocation images in X-ray topography of protein crystals: tetragonal hen egg-white lysozyme crystals

Dislocation images in X-ray topography of protein crystals such as tetragonal hen egg-white lysozyme crystals were analyzed. Not only extinction but also double contrast of dislocation images are clearly observed on the X-ray topographs. It should be noted that the observed image widths of the dislocation contrasts are much less than those calculated on the basis of the kinematical theory in X-ray topography, which has been successfully applied for inorganic crystals and organic crystals of small molecules so far. Moreover, in tetragonal HEW lysozyme crystals, the rocking curve widths of the perfect crystal related to the kinematical theory are less than the measured ones by two orders of magnitude. This discrepancy is consistent with that in the image width of the dislocation contrast. From this correlation, it is suggested that the larger rocking curve width, or higher mosaicity, is mainly responsible for the observed image width in the grown crystals.     

Ultrasound-assisted crystallization of high purity of 2,4-dinitrotoluene from spent acid

The high purity crystal of 2,4-dinitrotoluene (DNT) could be successfully recovered from spent acid in a short period through diluting method assisted with ultrasonic irradiation. The sonication tests were carried out to elucidate the influence of various ultrasonic powers on the performance of crystallization of 2,4-DNT. It is remarkable that under the supersaturated condition ultrasonic irradiation could significantly accelerate the crystal formation, in which the purity of 2,4-DNT reaches to approximate 98.9 wt%. Based on the particle size distribution of crystals, it is proposed that the enhancement on recovery rate of 2,4-DNT crystals by ultrasound is mainly ascribed to the elevation of mass transfer rate for crystal growth. According to the spectra examined by field emission scanning electron microscope (FESEM), the above hypothesis is further verified by the appearance of smoother surface of crystals. Furthermore, the results of metallurgical microscope measurements show that ultrasound has also an abrasive effect on 2,4-DNT crystals under high ultrasonic power inputs.     

Improving Beamline X-ray Optics by Analyzing the Damage to Crystallographic Structure

The mission of the X-ray Characterization Laboratory in the X-ray Science Division (XSD) at the Advanced Photon Source (APS) is to support both the users and the Optics Fabrication Facility that produces high-performance optics for synchrotron X-ray beamlines. The Topography Test Unit (TTU) in the X-ray Lab has been successfully used to characterize diffracting crystals and test monochromators by quantifying residual surface stresses. This topographic method has also been adapted for testing standard X-ray mirrors, characterizing concave crystal optics and, in principle, can be used to visualize residual stresses on any optic made from single crystalline material.     

Growth and characterization of l-histidinium 2-nitrobenzoate [LH2NB(I)]—A promising non linear optical single crystal

Single crystals of l-histidinium 2-nitrobenzoate [LH2NB(I)] have been successfully grown by slow evaporation method. The grown crystals have been subjected to powder X-ray diffraction studies and the cell parameters are calculated. The structural and optical properties of the grown crystals were characterized by FT-IR and UV–VIS–NIR studies. Photoconductivity and dielectric studies were also carried out for the grown crystals. Vickers microhardness test was also carried out to elucidate the mechanical behavior of the grown crystals. TG–DTG studies were carried out to determine the thermal stability of the crystals. The second harmonic generation behavior of the grown crystals was tested by Kurtz–Perry powder technique.     

Optically active helical polyurethane@attapulgite composites: Effect of optical purity of S-1,1′-binaphthyl-2,2′-diol on infrared emissivity

Helical polyurethane@attapulgite (HPU@ATT) composites were prepared after the surface modification of the rod-like attapulgite (ATT). HPU@ATT composites based on S-1,1′-binaphthyl-2,2′-diol (S-BINOL) with different optical purity (O.P.) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The rod-like nanoparticles were confirmed by transmission electron microscopy (TEM). Infrared emissivity values of HPU@ATT composites have been investigated, and the results indicate that the optical purity of monomer plays a very important role in the infrared emissivity for HPU@ATT owing to the effect of helical conformation and interchain hydrogen bonds. Along with the increased optical purity of S-BINOL, the infrared emissivity of HPU@ATT is reduced evidently. Infrared emissivity value of HPU@ATT based on S-BINOL with 100% optical purity is the lowest one (0.431).     

Crystal growth of superconductive PrBa2Cu3O7−y

Superconductive PrBa₂Cu₃O_7−y (Pr123) crystals have been grown successfully by the travelling-solvent floating-zone (TSFZ) method using 3.7–5.8% PrO, 27–37% BaO, and 60–69% CuO composition solution with the 0.1–0.4% oxygen mixed argon gas atmosphere. The grown crystals have been identified to be Pr123 by a precession camera, X-ray powder diffractions and scanning electron microscopy–X-ray energy dispersion spectroscopy (SEM-EDS). Some portion of the grown TSFZ crystal boules show bulk superconductivity below about 80 K after annealing in oxygen.     

Synthesis,growth of single crystals and their characterization: l-Alaninium maleate (LAM)

In recent days amino acid single crystals are gaining importance due to good optical behavior. The title compound consists of l-alanine; an amino acid and maleic acid; an aromatic organic compound. It has been successfully synthesized and the single crystal has been grown by slow evaporation solution growth. The grown single crystal has been characterized by powder X-ray diffraction (PXRD) analysis and FTIR measurements. The crystalline perfection was examined by high-resolution X-ray diffraction (HRXRD) technique and found that the specimen quality is quite good. Optical behavior has been assessed by UV–Vis analysis and found that there is no absorption in the entire visible region. The relative second harmonic generation (SHG) efficiency measurement reveals that the incorporation of maleic acid to l-alanine leads to increase its value of SHG. The mechanical behavior and the thermal analysis have been carried out using Vickers microhardness and TG/DTA measurements respectively. Its hyperpolarizability was estimated by density functional theory (DFT).     

Decisive role of polydispersity in the relaxation spectrum of saturated hydrocarbons from plasma-induced thermoluminescence data

The method of plasma-induced thermoluminescence for the first time has been used to investigate the molecular mobility in near-surface nanolayers of molecular crystals (paraffins) with different chain lengths. The investigations have been performed using a NanoLuminograph device (PlasmaChem, GmbH, Germany) under conditions excluding the modifying effect of gas discharge plasma emission on the surface structure under study. The origin of charge stabilization sites on the surface of molecular crystals as well as the influence of the chain length of paraffins and the purity of their chemical composition on the thermoluminescence intensity and the shape of the glow curves have been discussed.     

Synthesis,growth and characterization of 4-dimethylaminobenzaldehyde-4-nitrophenylhydrazone single crystals

4-Dimethylaminobenzaldehyde-4-nitrophenylhydrazone (DANPH) single crystals exhibit polymorphism such as DANPH-G form (greenish red) and DANPH-R form (red). The different polymorphic phases of the grown crystals have been identified by X-ray diffraction studies. The functional groups of the crystals have been identified by FT-IR study. Crystallographically independent environment of polymorphs has been confirmed by NMR study. The thermal properties such as melting and decomposition temperatures of the compound have been analyzed. Optical constants of DANPH polymorph crystals have been calculated.     

Electronic structure of BiSeI clusters

The valence band (VB) energy levels of BiSeI crystals have been calculated and compared to the X-ray photoelectron spectra of SbSI crystals. A molecular cluster consisting of 20 molecules of BiSeI has been used to calculate the total VB density of states by the density functional theory (DFT) method. The spectrum of total VB density of states of the (BiSeI)₂₀ cluster weighted by atomic photoemission cross-sections has been compared with the experimental X-ray photoelectron VB spectrum of SbSI type crystals. The cluster model calculation has showed that the core level energy splitting depends on the difference of ionic charges of the same atoms at the edges of the (BiSeI)₂₀ cluster.     

Studies on the growth aspects and characterization of sodium para-nitro phenolate single crystals for nonlinear optical applications

Using slow evaporation solution growth technique, single crystals of sodium para nitro phenolate have been grown from the solutions prepared from three different molecular ratios of para-nitro phenol and sodium hydroxide. Structural analyses were carried out by powder X-ray diffraction and Fourier transform infrared spectrum to conform the grown crystals. Thermal stability of the grown crystals was studied by thermogravimetric (TG) and differential thermal analyses (DTA). UV–vis spectral analysis has been carried out to find the cut off wavelength of the grown crystals. Variations in the cut off wavelengths have been observed. Nonlinear optical property has been confirmed by Kurtz powder technique. The observed optical properties have confirmed that the molar concentration of para nitro phenol influenced significantly on the linear and nonlinear optical properties.     

Enhancement of second harmonic generation efficiency: Cs(I)-doped tris(thiourea)zinc(II) sulphate crystals

The effect of dopant cesium (Cs(I)) over a concentration range from 1 to 10 mol% on the growth process, morphology, thermal and optical properties of tri(thiourea)zinc(II) sulfate (ZTS) single crystals grown by slow evaporation solution growth technique has been investigated. Incorporation of Cs(I) into the crystal lattice was well confirmed by energy dispersive X-ray spectroscopy (EDS). The lattice parameters of the as-grown crystals were obtained by single crystal X-ray diffraction analysis. The reduction in the intensities observed in powder X-ray diffraction patterns of doped specimen and slight shifts in vibrational frequencies in fourier transform infrared spectra (FT-IR) indicate the lattice stress as a result of doping. Thermal studies reveal the purity of the material and no decomposition is observed up to the melting point. High transmittance is observed in the visible region and the cut-off λ is ～280 nm. The surface morphology of the as-grown specimens was studied by scanning electron microscopy (SEM). The second harmonic generation (SHG) efficiency of the host crystal is enhanced greatly in the presence of high concentrations of the dopant.     

Some physical properties of ZnS crystals grown from the vapour phase

Wurtzite-type crystals with wide regions of high purity and good optical properties have been grown in a few hours by an improved flow method. Dislocations have been found to be mainly arranged inside isolated striation regions where a weak green fluorescence and phosphorescence has been observed. Under bending deformation the crystals show a plastic behaviour that is not directly correlated to the mean dislocation density of the samples. Rupture has been found at about 10³ kg/cm².The microwave method for the detection of crystal deflection has been suggested by Prof. A. Gozzini. His helpful advice and interest in this research has been deeply appreciated. Many thanks are also due to the Physical Institute of SAV in Prague, for the possibility to work on their crystals of ZnS. Finally we wish to thank Mr. Coli and Mr. Montanari for design and construction of the mechanical equipment and the furnace quartz assembly.     

Effect of urea and thiourea on nonlinear optical hippuric acid crystals

Pure, urea and thiourea doped hippuric acid (HA) single crystals have been grown in acetone using slow evaporation technique at a constant temperature, with the vision to improve the properties of the crystals. The crystal systems and the unit cell parameters of the grown crystals were identified from single crystal X-ray diffraction. The crystalline nature of the grown crystals was confirmed by powder X-ray diffraction and the diffraction peaks were indexed. The variations in composition due to the addition of dopants were identified by CHNS analysis. FT-IR studies reveal the presence of different vibrational bands. The optical characteristics were assessed by UV–vis analysis and it indicates the transmission in the visible region. TGA and DSC studies indicate the thermal behavior of pure and doped crystals. The Second Harmonic Generation (SHG) has been tested using Kurtz Powder Technique for the pure and doped crystals. It is found that the thiourea doped hippuric acid crystals have SHG efficiency of 2.08 times higher than that of potassium dihydrogen phosphate (KDP) single crystal. The dielectric studies were carried out, and the variations of dielectric constant and dielectric loss with temperature have been studied.     

Enhancement of second harmonic generation efficiency: Growth and characterization of magnesium(II)-doped tetrakis(thiourea)nickel(II) chloride crystals

The influence of magnesium doping on the properties of tetrakis(thiourea)nickel(II) chloride crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy. The incorporation of Mg(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Lattice parameters are determined by single crystal XRD analysis. The thermogravimetric and differential thermal analysis studies reveal the purity of the materials and no decomposition is observed up to the melting point. The crystal is further characterized by Kurtz powder technique and dielectric studies.