Direct melt crystal growth of isotactic polybutene‐1 trigonal phase

The morphology, crystalline structure and crystal growth kinetics of melt‐crystallized thin isotactic polybutene‐1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self‐seeding at atmospheric pressure using solution‐grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt‐crystallized isotactic polybutene‐1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in‐situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of 1‐phenyl‐3‐(propan‐2‐yl)‐1H‐pyrazol‐5‐ol single crystals

The synthesis of pyrazoles and its derivatives remains of great interest due to their wide applications in pharmaceutical and agrochemical industry. The 1‐phenyl‐3‐(propan‐2‐yl)‐1H‐pyrazol‐5‐ol was synthesized. The 1‐phenyl‐3‐(propan‐2‐yl)‐1H‐pyrazol‐5‐ol single crystals were grown by slow solvent evaporation technique using mixture of chloroform and methanol as a solvent. Yellowish and transparent crystals having maximum dimensions of 0.005 m × 0.004 m × 0.002 m were grown. The crystals were characterized by powder XRD, FT–IR, TG–DTA–DSC and dielectric study. The crystals remained stable up to 160 °C and then start decomposing. The DSC suggested both endothermic and exothermic reactions. One broad exothermic peak was observed at 558.1 °C due to complete decomposition of the sample into the gaseous phase and reaction within the products. Thermodynamic and Kinetic parameters of decomposition were calculated by Coats–Redfern formula. The dielectric study was carried out in the frequency range from 50 Hz to 5 MHz at room temperature. The dielectric constant decreased as the frequency of the applied field increased. The variations of dielectric loss, a.c. conductivity and a.c. resistivity also studied with the frequency of the applied field. Jonscher's power law was verified for a.c. conductivity.     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of gel grown iron‐manganese‐cobalt ternary levo‐tartrate crystals

In the present investigation, iron–manganese–cobalt ternary levo‐tartrate crystals of different compositions have been grown by single‐diffusion gel growth technique in silica hydrogel medium. The metallic composition in the crystals was estimated by EDAX. The coloration of the crystals changed with composition of metallic content. The powder XRD study suggested the crystalline nature and indicated the presence of some extra phases. The grown crystals were characterized by FT‐IR spectroscopy, TGA, dielectric and Vibrating Sample Magnetometer (VSM) studies. The FT‐IR study suggested the presence of O‐H, C=O, C‐O and metal‐oxygen bonds. The effect of composition of metallic content was observed in certain absorption regions in FT‐IR spectra. The thermal stability of the crystals was studied by thermogravimetry and the kinetic and thermodynamic parameters of dehydration were calculated. The effect of composition of ternary levo‐tartrate was observed in dielectric study. The dielectric study was carried out in the frequency range of applied field from 500 Hz to 1 MHz. The variations in dielectric constant, dielectric loss, a.c. resistivity and a.c. conductivity with frequency of applied field were studied. VSM study suggested that all crystals were of paramagnetic nature. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of nano‐crystalline hydroxyapatite at physiological conditions

Pure, stable stoichimetric nano crystalline hydroxyapatite material was crystallized by double diffusion technique at physiological conditions, temperature at 37°C and pH at 7.4. The sample was sintered at 400°C, 750°C and 1200°C with equal interval of time. They were characterized by X‐ray diffraction studies, Fourier Transformation Infra‐Red analysis, Thermogravimetric analysis, Scanning Electron Microscopic studies and Atomic Force Microscopic studies. The X‐ray analysis confirmed that the grown crystals are to be the pure form of hydroxyapatite. Infra‐red studies confirmed CO free hydroxyapatite. Thermogravimetric studies showed the thermal stability of the hydroxyapatite crystals even at 1200°C. The presence of pores in the sintered sample was traced by scanning electron microscopy. Atomic force microscopy revealed the presence of nano crystalline HAP of size 0.958 nanometer in the samples grown using this technique. At higher temperature the deagglomeration of bulk phases and agglomeration of nano phases leads to the nano crystalline HAP were observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of PbTe‐SnTe particles by thermal decomposition of salts to create nano‐structured thermoelectric materials

Micro‐ and nanocrystalline particles of Pb‐Sn‐Te mixed crystals were synthesized using thermal decomposition and chemical interaction of lead acetate, tin oxalate and tellurium powder mixture in H₂ atmosphere. For the process parameter optimization data of thermal gravimetry (TG), X‐ray diffraction (XRD), electronic microscopy (TEM, SEM) and measurements of the specific surface of particles were used. Additionally the influence of gas phases on the decomposition kinetics, crystal structure, size, specific surface of the particles, gains composition and the physical properties were analyzed. Seebeck coefficient values increased and conductivity decreased with decreasing tin concentration. The presented method for preparing PbTe‐SnTe polydisperse particles is developed to create nano‐structured thermoelectric materials with high figure of merit. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Singular ring‐shaped distribution of Nd in NdxY1‐xVO4 crystals grown by floating zone method

A singular ring‐shaped distribution of high Nd concentration was observed in Nd‐doped YVO₄ single crystals grown by the floating zone (FZ) method. The ring‐shaped distribution appeared 500‐1000 μm inside from the rim of the crystals. Results of growth experiments by the anisotropic heating floating zone (AHFZ) method showed that the Nd concentration was high at the high‐temperature side of the grown crystals. We found a small concave projection at a part of the convex solid‐liquid interface by quenching the molten zone during growth. The cause of the singular ring‐shaped distribution of the Nd‐rich area was discussed in relation with the concave projection at the interface and the convection in the molten zone. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of nano‐crystalline zeolite β: Effects of crystallization parameters

The effects of variation in Si/Al ratio (25 and 100) and crystallization temperature (80 °C to 180 °C, at an interval of 20 K) on crystal size of zeolite β were studied. Products obtained at different synthesis parameters were characterized by powder X‐ray diffraction, IR spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption. Increase in crystal size with crystallization temperature and Si/Al molar ratio was observed. Crystal morphology at 140 °C was spherical whereas at 180 °C it was of irregular shape. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nd(III) and Yb(III) ions incorporated in Y4Al2O9 obtained by sol‐gel method: synthesis,structure, crystals and luminescence

The nanocrystalline powders of Y₄Al₂O₉ (YAM) pure and doped by Nd, Yb and codoped by Nd and Yb were obtained via modified sol‐gel method. These powders were characterized by X‐ray diffraction method, scanning electron microscopy and high resolution scanning electron microscopy, luminescence spectroscopy and differential thermal analysis (DTA). We obtained single phase powders of crystalline structure with average size 70 nm exhibiting interesting luminescent properties. Efficient non‐radiative energy transfer between Nd and Yb was found. DTA confirmed the phase transition at about 1400 °C. From these nanocrystalline powders, the crystals YAM:Yb, YAM:Yb,Nd were grown by micro‐pulling down technique. They were cracking during cooling owing to the phase transition. Luminescent properties of YAM:Nd,Yb crystals were identical with properties of corresponding nanopowders within experimental incertitude. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation and ageing of L‐glutamic acid spherulites

Polycrystalline spherulites of L‐glutamic acid have been crystallized by pH‐shift precipitation from stirred aqueous solutions. The time dependent behaviour of the spherulites has been studied during the crystallization process and batch filtration tests have been performed. It has been shown that the FBRM mean chord length of the investigated spherulites decreases in the course of time. The fact that the size reduction progresses faster at higher temperature and the solubility of resuspended polycrystalline particles decreasing with time, implies an ageing mechanism to be responsible for the observed changes in the particle size. It has been shown that the surface area decreases with time, ruling out particle breakage as a possible explanation for the decrease in particle size. XRD and Raman studies of L‐glutamic acid, however, show only marginal differences in the crystalline structure of particles obtained from different time stages. The ageing may occur due to several different mechanisms like phase transformation and Ostwald ripening. L‐glutamic acid spherulites after 3 h exhibit a 3‐fold higher value for the cake resistance as compared to particles after 0.5 h. However, particles obtained after 22 h exhibit an 8‐fold lower cake resistance as compared to the initially obtained spherulites, The increase in the cake resistance is attributed to the appearance of small plate‐like crystals and a change in the interaction between the crystal surface and the solution. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Agglomeration of NTO on the surface of HMX particles in water‐NMP solvent

A sensitive explosive was coated with a less sensitive explosive in order to improve stability while maintaining explosion performance. Agglomeration of 3‐nitro‐1,2,4‐triazole‐5‐one (NTO) on the surface of cyclotetramethylene tetranitramine (HMX) crystals in water‐N ‐methyl‐2‐pyrrolidone (NMP) solvent was performed by cooling crystallization. Phenomena for coating by crystallization and agglomeration were studied by in‐situ measurement. The agglomeration kinetic for the coating of NTO on HMX crystals was correlated with the 3rd power of the solution supersaturation and the 2nd power of the number of the suspended particles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Study on Carbon Incorporation in Semi‐Insulating GaAs Crystals Grown by the Vapor Pressure Controlled Czochralski Technique (VCz) Part I: Experiments and Results

In the past it has been demonstrated that the carbon concentration of large semi‐insulating (SI) GaAs single crystals grown by the conventional liquid encapsulation Czochralski (LEC) technique can be controlled by several methods including variations of growth parameters. It was the aim of the present paper to clarify which of the relationships of LEC growth could be used for a carbon control in the VCz‐method characterized by the application of an inner chamber made from graphite to avoid selective As evaporation. In detail this comprised a study of the influence of several growth parameters like the water content of the boric oxide, the composition of the working atmosphere, the gas flow, a titanium gettering and additions of gallium oxide. As a result, for the first time carbon concentrations down to ≈ 1014 cm^‐3 were obtained in 3'' (75 mm) diameter VCz crystals.     

Syntheses and X‐Ray crystal structures of aminated 4,4'‐Bi‐1,2,4‐triazole salts

3‐Amino‐4,4'‐bi‐1,2,4‐triazole hydrochlorate and 3,3'‐diamino‐4,4'‐bi‐1,2,4‐triazole ditosylate were obtained with the reduction of 3,3',5,5'‐tetraazide‐4,4'‐bi‐1,2,4‐triazole (TABT) by (Ph)₃P/H₂O and the followed salt forming reaction with concentrated HCl and aqueous TsOH, respectively. Their structures were characterized with elemental analyses, IR, MS, ¹H and ¹³C NMR spectra. The single crystals were cultivated and determined with X‐ray diffraction, test results reveal that H⁺ combines with electron‐rich N atom in triazole ring to form ionic salts, two N,N‐linked triazoles are almost perpendicular to each other due to lower steric hindrance. The aromatic π…π stacking interactions and hydrogen bonds between molecules are observed. These two novel salts and their derivatives may be applied in coordination chemistry, medicinal chemistry and energetic materials.     

Elastic and elasto‐optical properties of Rb1–x(NH4)xH2AsO4 mixed crystals studied by Brillouin spectroscopy

The elastic and elasto‐optical properties of Rb_1–x (NH₄)_x H₂AsO₄ mixed crystals were studied by Brillouin spectroscopy at room temperature. The measurements were made on single crystals obtained from the aqueous solution by slow evaporation. The behaviour of bulk phonons propagating in investigated crystals was studied for different polarisations of incident and scattered beam. The components of the tensors of elasto‐optical and elastic properties of the crystals studied were determined. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of L‐lysine monohydrochloride dihydrate (L‐LMHCl) single crystal

A nonlinear optical crystal of L‐lysine monohydrochloride dihydrate (L‐LMHCl) was grown by slow evaporation solution growth technique using deionised water and mixed solvents of deionised water and ethanol. The functional groups and vibrational frequencies were identified using FTIR and FT‐RAMAN spectra analyses. Also, the presence of hydrogen and carbon atoms in the grown sample was confirmed using proton and carbon NMR spectra analyses. Using TG‐DTA analyses, the decomposition temperature was obtained. Transmittance of the grown crystals was analysed using UV‐visible spectrum. The mechanical strength of the grown crystals was found using Vicker's microhardness tester. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Floating zone growth and characterization of ruby single crystals

Large, high optical quality single crystals of ruby have been grown successfully by the floating zone method under air atmosphere. The size of the grown crystal is typically 60‐70 mm in length and 7‐8 mm in diameter. The obtained crystals were red and did not have any macroscopic defects such as cracks and inclusions. Grown crystals were characterized by powder X‐ray diffraction (XRD) methods, polarized optical microscopy, scanning electron microscopy (SEM). The absorption and fluorescence spectra were measured at room temperature and the dielectric constant measurements of ruby crystals were also presented. Defects occurring in single crystals of ruby during crystal growth by floating zone method are described, and their correlation with the growth parameters is discussed. The origin and control of these defects in grown crystals were studied and the optimum method was proposed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Bacillus subtilis on the growth of calcium oxalate

The influence of the bacteria Bacillus subtilis (B. subtilis) on the nucleation, growth and aggregation of calcium oxalate (CaOx) crystals in aqueous solution has been studied. The crystals obtained were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X‐ray powder diffractometry. The results show that, in the presence of B. subtilis, quasi‐hexagonal calcium oxalate monohydrate (COM) crystals are obtained after 24 hours of reaction at a temperature of 30°C ± 1K. However, without the presence of the bacteria, irregular CaOx crystals were obtained which contain two crystal phases: COM and calcium oxalate dihydrate (COD). This suggests that B. subtilis may promote the crystallization of COM, the major component of urinary stone. The formation mechanism of CaOx crystals in the presence of B. subtilis is explored, indicating that the cell walls and extracellular proteins of the bacteria may act as templates to induce the nucleation, growth and aggregation of CaOx crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical,mechanical and thermal properties of p‐bromoacetanilide

Solubility and metastable zonewidth were estimated for p‐Bromoacetanilide. Employing slow evaporation method crystals of size 22x17x6 mm³ and 38x25x10 mm³ were grown at a constant temperature of 40°C and room temperature respectively from methanol solution. The cell dimensions were obtained by single crystal X‐ray diffraction study. The placement of protons was identified from NMR spectral analysis. UV‐Visible and fluorescence spectral analyses were carried out for the grown crystals. Vickers microhardness test was performed on the prominent (110) of the as grown crystal. Thermogravimetric and differential scanning calorimetric studies were carried out to determine the thermal properties of the grown crystal. (© 2006 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)     

Flux growth of straw‐like rutile monocrystals

Millimetric straw‐like rutile monocrystals were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and amorphous TiO₂ gel was slowly cooled down to 750°C from 1250°C or 1350°C. The best yields of straw‐like rutile were obtained with a nutrient/flux ratio and a cooling rate in the range 0.015‐0.006 and 1.8‐1.9 K h^‐1, respectively. The hollowed crystals were characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy, microthermometry, and µ‐Raman spectroscopy. As for skeletal crystal, the formation of axial canals in rutile is attributed to a lack of nutrient due to the viscosity of the melt and the high growth rate along [001]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)