Growth Habit and Habit Variation of γ‐CuI Crystallites under Hydrothermal Conditions

The octahedra were observed in the γ CuI crystallites synthesized by hydrothermal method using 1.6g (C₂H₅OO)₂Cu and 2.66g KI as precursors at 200 °C for 12 hours in the de‐ionized water. The effect of additives on the morphology of γ‐CuI crystallites was investigated. Results show that the morphology of γ‐CuI crystallites prepared in the mixed solution of de‐ionized water and alcohol at 200 °C for 12 hours is the tetrahedron. In order to disclose the effect of the additive on the growth habit of γ‐CuI crystallites, the microcosmic growth mechanism of γ‐CuI crystal is investigated from the complex of I^‐ and Cu⁺ ions to each other. It is concluded that the effect of alcohol on the morphology of γ‐CuI crystallites is carried out through changing the relative rate of complex of anion and cation to each other at the interface. Based on the above analysis, the growth habit of γ‐CuI crystallites and the habit variation under hydrothermal conditions are explained reasonably.     

Crystal growth,optical, mechanical and electrical properties of organic NLO material γ‐glycine

Single crystals of organic non‐linear optical material, γ‐glycine have been grown by gel method for the first time. The γ‐phase is confirmed by single crystal XRD. The presence of various functional groups of γ‐glycine are confirmed by FTIR. The UV‐Vis‐NIR spectrum reveals the high percentage of transmission of the sample in the entire visible region. The SHG of γ‐glycine is confirmed by Kurtz powder technique. TGA‐DTA studies indicate that the crystal is structurally stable upto 170 °C. Microhardness investigations are conducted on the grown crystals. The dielectric constant measurements are carried out and the nature of variation of dielectric constant ε′ and dielectric loss D in the frequency range of 50 Hz to 5 MHz is studied and reported. Photoconductivity studies of γ‐glycine crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Recharging processes of Cr ions in Mg2SiO4 and Y3Al5O12 crystals under influence of annealing and γ ‐ irradiation

Recharging processes of chromium ions were investigated for Mg₂SiO₄:Mg, Cr single crystals using annealing in O₂ and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg₂SiO₄ :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O₂‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr³⁺ and Cr⁴⁺ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr³⁺ and Cr⁴⁺. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr⁴⁺ giving rise to Cr⁴⁺ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of strontium chloride on the optical and mechanical properties of γ–glycine crystals

Single crystals of γ‐glycine have been grown from aqueous solution in the presence of small amount of strontium chloride. Single crystal X‐Ray diffraction analysis was used to measure the unit cell parameters and to confirm the crystal structure. The grown crystals have also been subjected to powder X‐Ray diffraction study to identify the crystalline nature. The presence of all the functional groups of the γ‐glycine has been confirmed by Fourier Transform Infrared (FTIR) spectral analysis. The presence of hydrogen and carbon in the glycine molecules was confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. Optical behavior of the crystal was studied using UV – Visible absorbance spectroscopy and second harmonic generation (SHG) studies. The SHG efficiency of γ‐glycine is greater than that of standard potassium dihydrogen phosphate (KDP). Mechanical strength of the γ‐glycine crystal has been determined by microhardness studies. Thermal stability of the grown crystal is probed using thermo gravimetric analysis and differential thermal analysis. Laser damage threshold value has been determined using Q‐switched Nd:YAG laser operating at 1064 nm and with 13 ns pulse width in single shot mode. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects induced by chemical non‐stoichiometry and γ‐irradiation on the habit and unit cell parameters of ammonium tetrachlorozincate

The effect of chemical non‐stoichiometry and γ‐irradiation on the unit cell parameters of ammonium tetrachlorozincate (NH₄)₂ZnCl₄ (A₂ZC₄) has been studied. The unit cell parameters of crystal grown from solution with NH₄Cl/ZnCl₂ molar ratio 1:1, apparently non‐stoichiometrric, are nearly the same as those given for ammonium tetrachlorozincate in the literature. The 2:1 ratio is actually ‘pseudo‐stoichiometric’ due to the hygroscopic nature of ZnCl₂. The unit cell parameters of crystal grown from solution with molar ratio 2:1 match those of the structure (NH₄)₃ZnCl₅ (A₃ZC₅). The habit of the crystal grown in the former case, from solution with excess ZnCl₂, was different from that of the crystal grown in the later case, from solution with excess (NH₄)Cl. Between these two limits, a set of four samples were prepared from solutions with an excess of ZnCl₂ of 20, 30, 60 and 80 wt% in order to detect exact stoichiometric composition to grow A₂ZC₄. Analysis by X‐ray diffraction shows that the first two crystals out of this set are mixed from A₂ZC₄ and A₃ZC₅ The third and fourth crystals still contain traces of A₃ZC₅. Analysis of the X‐ray diffraction was then confirmed by DTA study. Irradiating A₂ZC₄ with γ‐dose of 250 kGy slightly increased the unit cell volume due to imperfections created by irradiation. Two computer programs were used to calculate the lattice constants and the results were compared. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of β‐glycine by spray drying

Glycine crystallization during spray drying has been investigated on a laboratory scale. In order to obtain different polymorphs the experiments have been performed at different hot air temperatures, concentrations, different flow of the solution and spraying air. The obtained crystals were analyzed by means of X‐ray powder diffractometry, differential scanning calorimetry and the Fourier transform infrared spectrometry. Crystallization mostly resulted with a mixture of α‐ and β‐glycine with a small amount of γ‐glycine. The glycine polymorphism is affected by the drying air temperature, concentration and the flow of the solution, as well as the spraying air flow. Decrease of the drying air temperature and increase of the solution flow rate causes the increase of the quantity of β‐glycine. At room conditions, β‐glycine spontaneously transforms into thermodynamically more stable α‐glycine. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic field dependence of the relative critical current density in γ‐irradiated polycrystalline YBa2Cu3O7

The effect of different doses of γ‐rays on the behavior of the critical current density, J_c in an YBa₂Cu₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ‐ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 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).     

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)     

Growth and downconversion luminescence of Ho3+/Yb3+ codoped α‐NaYF4 single crystals by the Bridgman method using a KF flux

Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho³⁺/Yb³⁺ codoped α‐NaYF₄ single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF₃ system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho³⁺ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb³⁺ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF₄ single crystals of 0.799 mol% Ho³⁺ and 15.15 mol% Yb³⁺. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho³⁺ to Yb³⁺ increases, which may result from the fluorescence quenching between Ho³⁺ and Yb³⁺ ions, Yb³⁺ and Yb³⁺ ions.     

α‐Fe2O3 nanospindles loaded with ZnO nanocrystals: Synthesis and improved gas sensing performance

ZnO/α‐Fe₂O₃ nanocomposites were fabricated through a two‐step hydrothermal method. The morphology and composition of the as‐synthesized products were characterized by X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The gas sensing properties of the fabricated products were investigated towards ethanol, acetone, propanol, isopropanol, formaldehyde, chloroform and so on. The results demonstrated that the ZnO/α‐Fe₂O₃ nanocomposites exhibited excellent sensing properties and showed remarkably higher sensing responses and much lower optimum operating temperature compared to individual ZnO and α‐Fe₂O₃. In addition, the ZnO/α‐Fe₂O₃ nanocomposites have some selectivity for ethanol, propanol and isopropanol. The possible gas sensing mechanism was also proposed. Our studies demonstrate that our fabricated materials could be widely used in the future.     

Experimental study of bubble generation during β‐BaB2O4 single crystal growth

The generation of bubble‐inclusions during BaB₂O₄ (BBO) crystal growth from high temperature solution has been optically observed by an in situ observation technique. It was found that bubbles are formed from the peripheries of some hexagonal defects in the (0001) plane of the growing crystal, which may be caused by the evaporation of the air‐opened interface at the high temperature. In addition, atomic force microscope (AFM) was used to investigate the distribution of bubbles. Results revealed that the bubble generation and distribution depend strongly on the microscopic structure of the interface: on a rough interface, bubbles are easily formed and grow rapidly; however, they are greatly suppressed by step trains on a vicinal interface. In the latter case, the height value of a bubble is close to that of the step, which is in the order of several tens of nanometers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,etching morphology and spectra of LiAlO2 crystal

γ‐LiAlO₂ single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X‐ray rocking curve and chemical etching. The effects of air‐annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO₂ were also investigated in detail. The results show that the as‐grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7‐22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×10³ cm^–2. The VTE‐treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air‐annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization and crystal structure of a novel Ni(II) coordination polymer with dipyrido[3,2‐a:2′,3′‐c]phenazine and 4,4′‐oxy(bisbenzoate)

A novel coordination polymer, [Ni(dppz)(oba)(H₂O)]·0.5H₂O (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine and oba = 4,4′‐oxy(bisbenzoate)) has been synthesized through hydrothermal method and characterized by IR, and single‐crystal X‐ray diffraction. It crystallizes in monoclinic, space group C2/c with a = 23.163(5), b = 18.211(4), c = 14.460(3) Å, α = γ = 90°, β = 100.45(3)°, V = 5998(2) ų, Z = 2. The structure was solved by direct methods and refined to R = 0.0866 (wR₂ = 0.1836). The compound exhibits interesting one‐dimensional chain structures, which are further stacked through π‐π interactions to form supramolecular double chains. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of 3‐(3‐nitrophenylhydrazonocarbonyl)‐(1H)‐1,2,4‐triazole

The title compound, C₁₀H₈N₆O₃, was synthesized by the reaction of 3‐(1H)‐1,2,4‐triazole hydrazine with 3‐nitrobenzaldehyde in ethanol. The single crystal structure has been determined by X‐ray analysis. The crystal belongs to monoclinic system, space group p2₁/c with cell constant, a = 8.0214(17) Å, b = 17.334(4) Å, c = 8.9070(18) Å, V= 1179.4(4) ų. An intramolecular N—H...O and N—H…N hydrogen bond are observed between the ‐NH group with O atom of the carbonyl group and the ‐NH group with N atom. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile hydrothermal synthesis of uniform 3D γ‐AlOOH architectures assembled by nanosheets

Uniform γ‐AlOOH architectures assembled by nanosheets were successfully synthesized in the mixture of deinonized water and dimethyl sulfoxide (DMSO) at 180 °C. The structure and morphology of products were characterized by X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The products displayed 3D microstructures with its length of 1 μm and diameter of 400‐500 nm. The obtained γ‐AlOOH structures exhibited large Brunauer‐Emmett‐Teller (BET) surface area of 216.5 m²/g and pore size of 3.7 nm. The formation mechanism of 3D γ‐AlOOH architectures was also discussed based on the experimental results. Furthermore, the γ‐AlOOH architectures exhibited preliminary photoluminescence (PL) phenomenon with a strong peak at 323 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystal structure of α‐SrGaBO4

A new compound α‐SrGaBO₄ has been synthesized by solid state reaction at high temperatures, and its structure has been solved by direct methods from powder X‐ray diffraction. α‐SrGaBO₄ has an orthorhombic system, Pccn space group, with lattice parameters a = 15.3154(7) Å, b = 8.9186(4) Å, c = 5.8130(3) Å, and Z = 8. The structure consists of infinite chains run parallel to the c axis and built up of GaO₄ tetrahedral and BO₃ triangles. The basic unit of these chains is a six ‐ membered Ga₂BO₈ ring formed by two GaO₄ tetrahedra and one BO₃ triangles. The Sr atom is bonded to eight oxygen atoms. The strontium atoms serve to hold the chains together through co‐ordination with oxygen atoms. DTA curve of noncrystalline glassy SrGaBO₄ was discussed. The XRD results show no phase transition occurs between ‐173 °C and 127 °C. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Point and extended defects in superconductors

The effect of point defects created by γ‐irradiation and extended defects created by Pb‐ion irradiation on the behavior of the critical current density, J_c in several superconductors have been investigated. We have found a limitation of the role of both types of defects on enhancing J_c. We report an explanation of the effect of γ‐irradiation and Pb‐ion irradiation doses on J_c in these materials. The explanation is based on combining several competing mechanisms of irradiation which we believe to take place mainly in the regions of the grain boundaries. The influences of these mechanisms were found to vary with the irradiation dose level. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)