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Orthorhombic Structure (orthorhombic + structure)
Selected AbstractsPreparation of shuttle-like Sb2S3 nanorod-bundles via a solvothermal approach under alkaline conditionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2010Ling Zhang Abstract Uniform shuttle-like Sb2S3 nanorod-bundles were synthesized via a polyvinylpyrrolidone (PVP) assisted solvothermal approach under alkaline condition, using antimony chloride (SbCl3) and thiourea (CH4N2S, Tu) as the starting materials in ethanol. The phase structure, composition and morphology of the product were characterized by means of X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). XRD and EDS results confirm that the synthesized Sb2S3 nanorod-bundles have an orthorhombic structure and an atomic ratio of 3:2 for S:Sb. TEM and HRTEM results show that the shuttle-like Sb2S3 bundles are composed of nanorods with a size distribution of 20-40 nm and growing along c-axis. Furthermore, experiments under different reaction conditions were carried out and the mechanism for the growth of nanorod-bundles was discussed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydrothermal Synthesis and Characterization of KxNa(1,x)NbO3 PowdersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2007Jun-Hai Lv NaNbO3, KNbO3, and KxNa(1,x)NbO3 powders were successfully prepared by the hydrothermal method. The phase of the products was identified to be orthorhombic structure by X-ray diffraction (XRD) technique, and the XRD results revealed that the x value of the KxNa(1,x)NbO3 gradually increased with the increase in the ratio of K+ to Na+ in alkaline solution. The morphology and the microstructure were investigated by scanning electron microscopy, energy-dispersive spectroscopy, and transmission electron microscopy, and the results indicated that the ratio of K+ to Na+ in the solution had a great effect on the morphology and the size of products. Na0.5K0.5NbO3 with morphotropic phase boundary composition could be synthesized when the molar ratio of K+ to Na+ was between 4:1 and 6:1 in the solution. A possible formation mechanism of the KxNa(1,x)NbO3 crystal was also proposed based on the experimental results. [source] Thickness-Driven Orthorhombic to Triclinic Phase Transformation in Pentacene Thin Films,ADVANCED MATERIALS, Issue 7 2005F. Drummy Pentacene films are thermally evaporated onto amorphous carbon-coated mica substrates held at room temperature. The crystal structure and morphology of the films are analyzed using electron microscopy and diffraction, and a new orthorhombic structure is characterized for films below a critical thickness (see Figure). Evidence that the orthorhombic structure is thermodynamically stable at low film thickness due to its low (001) surface energy is obtained. [source] XRD studies, vibrational spectra, and molecular structure of 1H-imidazo [4,5-b]pyridine based on DFT quantum chemical calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010L. Dymi Abstract The molecular structures and vibrational properties of 1H -imidazo[4,5-b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X-ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee,Yang,Parr correlation functional (B3LYP) and 6-31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna21(C2v9) and Z = 4. The planar conformation of the skeleton and presence of the NH···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4,294 K and 8,295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd. [source] Raman spectroscopic study on the structure, phase transition and restoration of zirconium tungstate blocks synthesized with a CO2 laserJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2007E. J. Liang Abstract Densely packed zirconium tungstate blocks were synthesized by rapid solidification with a CO2 laser. The structure and phase transition properties of the samples were studied by Raman spectroscopy and X-ray diffraction. Raman spectroscopic study reveals that zirconium tungstate solidifies with an orthorhombic structure. This is attributed to the pressure encountered by the samples during rapid solidification. Several Raman bands change discontinuously at about 390 K, indicating a phase transition from the ,- to the ,-phase occurring at this temperature. In the ,-phase, most of the Raman modes give rise to negative Grüneisen parameters, suggesting contribution of the corresponding optical phonons to the negative thermal expansion coefficient of the material, at least for the ,-phase. A recovery of the ,-phase was observed when the samples were cooled to room temperature. This suggests that the cubic structure is metastable only at temperatures above 390 K, and at room temperature the ,-phase is preferred. Copyright © 2007 John Wiley & Sons, Ltd. [source] Structural and Dielectric Characterization of Nanocrystalline (Ba, Pb)ZrO3 Developed by Reverse Micellar SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Tokeer Ahmad Nanocrystalline zirconates of barium and lead have been synthesized using a modified reverse micellar route (avoiding alkoxides). The entire solid solution of Ba1,xPbxZrO3 (0,x,1) has been synthesized for the first time. Powder X-ray diffraction studies show the monophasic nature of the powders after heating at 800°C except minor impurities of ZrO2 (2%,3%) at a higher lead content (x=0.50 and 0.75). The oxides crystallize in the cubic structure till x=0.25; for higher values, they crystallize in the orthorhombic structure. The particle size obtained from X-ray line-broadening studies and transmission electron microscopic studies is found to be in the range of 20,60 nm for all the oxides obtained after heating at 800oC. The grain size of the solid solution of Ba1,xPbxZrO3 (0,x,1) was found to increase with the lead content. The dielectric constant of the solids corresponding to Ba1,xPbxZrO3 (0,x,1) was found to be a maximum at x=0.50. Note that the cubic to orthorhombic transition is also observed between x=0.25 and 0.5. Dielectric properties with respect to variation in frequency and temperature are reported for these nanocrystalline oxides for the first time. [source] Negative Thermal Expansion in (HfMg)(WO4)3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Tomoko Suzuki A single-phase material (HfMg)(WO4)3 with an orthorhombic structure, A2 (WO4)3 -type tungstate, has been successfully prepared for the first time by the calcination of HfO2, MgO, and WO3, substituting Hf4+ and Mg2+ for A3+ cations in A2(WO4)3. The new material shows a negative thermal expansion coefficient of approximately ,2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2(WO4)3. [source] Cyclodextrins in Polymer Synthesis: Enzymatic Polymerization of a 2,6-Dimethyl- , -Cyclodextrin/2,4-Dihydroxyphenyl-4,-Hydroxybenzylketone Host-Guest Complex Catalyzed by Horseradish Peroxidase (HRP)MACROMOLECULAR BIOSCIENCE, Issue 8 2003Lorenzo Mejias Abstract This paper reports the enzymatic polymerization of the inclusion complex 2,4-dihydroxyphenyl-4,-hydroxybenzylketone/2,6-dimethyl- , -cyclodextrin by horseradish peroxidase (HRP) in aqueous media. The structure of the complex was determined by means of NOESY-NMR and crystallographic analysis (indicating an orthorhombic structure). The enzymatic polymerization of the uncomplexed 2,4-dihydroxyphenyl-4,-hydroxybenzylketone yields oligomers with molecular weights up to in organic-aqueous media, but because of its poor solubility in aqueous systems, no polymerization is observed if water is used as solvent. An increase of the availability of the ketone in solution is achieved by complexing it with random-methylated , -cyclodextrin in water. We found that the use of methylated , -cyclodextrin in equimolar concentration to the monomer increases the polymerization yield and the average molecular weight. The polymers formed were analyzed by GPC and ATR-FTIR techniques. Representation from X-ray diffraction analysis of the 2,6-dimethyl- , -cyclodextrin/2,4-dihydroxyphenyl-4,-hydroxybenzylketone host-guest complex (3). [source] Optical properties and structural phase transitions of lead-halide based inorganic,organic 3D and 2D perovskite semiconductors under high pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2004K. Matsuishi Abstract Optical absorption, photoluminescence and Raman scattering of lead-halide based inorganic,organic perovskite semiconductors were measured under quasi-hydrostatic pressure at room temperature. For the 3D perovskite semiconductor, (CH3NH3)PbBr3, the free exciton photoluminescence band exhibits red-shifts with pressure, and jumps to a higher energy by 0.07 eV at 0.8 GPa, which is associated with a phase transition from a cubic to an orthorhombic structure confirmed by Raman scattering. Above the phase transition pressure, the exciton band shows blue-shifts with further increasing pressure, and eventually disappears above 4.7 GPa. The results are compared with those for the 2D perovskite semiconductor, (C4H9NH3)2PbI4. First principles pseudopotential calculations were performed to investigate changes in octahedral distortion and electronic band structures with pressure. The calculations have explained the origins of the intriguing changes in the electronic states with pressure in view of bonding characters between atomic orbitals in octahedra. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impact of ultraviolet radiation on HDPE and HDPE/STC blendsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2009Min Qiao Abstract The structure and properties of high-density polyethylene (HDPE) ultraviolet irradiated in ozone atmosphere were studied by FTIR, XPS, GPC, XRD, DSC, TG, gel, and contact angle test. The oxygen-containing groups such as CO, CO, and C(O)O were quickly introduced onto HDPE chains through ultraviolet irradiation in ozone atmosphere; their content increased with increase in the time of ultraviolet irradiation. Compared with those of HDPE, the molecular weight of the irradiated HDPE decreased and its distribution became wider. There was no gel in the HDPE irradiated in ozone atmosphere. After ultraviolet irradiation for short times in ozone atmosphere, the water contact angle of the irradiated HDPE decreased and its hydrophilicity was improved. The crystal shape of the irradiated HDPE was still an orthorhombic structure; its cell parameter and the face space did not alter, but its melting temperature decreased slightly. Compared with that of HDPE, the temperature of initial weight loss for irradiated HDPE decreased. The irradiated HDPE/sericite-tridymite-cristobalite (STC) blends were prepared. The dispersion and compatibility of the irradiated HDPE/STC blends were improved compared with those of HDPE/STC blends; thus its mechanical properties increased. Copyright © 2008 John Wiley & Sons, Ltd. [source] Complex disorder in ,-NH4Fe2(PO4)2: deciphering from a five-dimensional formalismACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2007Olivier Pérez A new mixed-valent iron ammonium phosphate, ,-NH4Fe2(PO4)2, has been synthesized. The diffuse scattering observed on the diffraction patterns implies complex disorder phenomena and prevents a direct structure resolution. The latter can be solved by generating an artificially ordered orthorhombic structure, using a five-dimensional approach and performing partial integration of the diffuse streaks. In the artificially ordered structure, hexagonal tunnels, delimited by FeO6 octahedra, perpendicular to the directions [011] and [01] can then be seen; they are filled either by [FeP2O10], zigzag ribbons or by NH cations. It is shown that the disordering originates from the shifting of adjacent (100) tunnel slices of the structure with respect to each other along [011], allowing the formation of either new commensurate (superstructure) or incommensurate modulations, or even complete disorder along a. The close relationships with the ordered monoclinic form ,-NH4Fe2(PO4)2 are also explained by this description. [source] Structure determination and phase transition behaviour of dimethyl sulfateACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2006Mark T. F. Telling The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241,K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below ,175,K the crystal transforms to a monoclinic structure (II) in the space group I2/a. The molecule is located on a twofold axis (Z, = 1/2) in both structures. The phase transition is of first order with strong hysteresis. The phase transition results in changes to both the intra- and the intermolecular coordination environment. [source] Two new polymorphs of diphenyl(4-pyridyl)methyl methacrylateACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2004Gerrit Gobius du Sart The title compound (D4PyMA), C22H19NO2, exhibits polymorphism after crystallization by slow evaporation from a binary mixture of chloroform and hexane. Long needle-like crystals have an orthorhombic structure (space group Fdd2), with one molecule in the asymmetric unit, while small tablet-like crystals exhibit a monoclinic crystal structure (space group P21/n), in which two independent but chemically identical molecules comprise the asymmetric unit. The bond lengths and angles are normal, while the torsion angles around the ,C,O, bond linking the diphenyl(4-pyridyl)methyl and methacrylate groups show the flexibility of the molecule by way of packing effects. The two polymorphs both contain weak C,H,, and C,H,O/N contacts but have different conformations. [source] Structure of tetragonal crystals of human erythrocyte catalaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2001Martin K. Safo The structure of catalase from human erythrocytes (HEC) was determined in tetragonal crystals of space group I41 by molecular-replacement methods, using the orthorhombic crystal structure as a search model. It was then refined in a unit cell of dimensions a = b = 203.6 and c = 144.6,Å, yielding R and Rfree of 0.196 and 0.244, respectively, for all data at 2.4,Å resolution. A major difference of the HEC structure in the tetragonal crystal compared with the orthorhombic structure was the omission of a 20-residue N-terminal segment corresponding to the first exon of the human catalase gene. The overall structures were otherwise identical in both crystal forms. The NADPH-binding sites were empty in all four subunits and bound water molecules were observed at the active sites. The structure of the C-terminal segment, which corresponds to the last exon, remained undetermined. The tetragonal crystals showed a pseudo-4122 symmetry in molecular packing. Two similar types of lattice contact interfaces between the HEC tetramers were observed; they were related by the pseudo-dyad axes. [source] Metastability of Corundum-Type In2O3CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2008Aleksander Gurlo Dr. Abstract The description of structural relations between bixbyite- and corundum-type structures is of particular interest because of the common occurrence of both structures. One of the representative examples of the bixbyite to corundum transition is the high-pressure high-temperature synthesis of the corundum-type indium oxide. The wet chemistry synthesis and stabilisation of the corundum-type In2O3 under ambient pressure conditions calls for a re-interpretation of the InO phase diagram as well as for the clarification of the phase transitions in In2O3. One of the questions to be clarified is the stability of the corundum-type In2O3. In the present work we studied the stability of the corundum-type In2O3 both theoretically (by density-functional calculations) and experimentally. The synthesis of the corundum-type In2O3 was performed by the modified non-alkoxide sol,gel method based on the ammonia-induced hydrolysis of indium nitrate in methanol. The corundum-type In2O3 was subjected to thermal analysis (STA) as well as to structural studies, that is, it was examined using X-ray powder diffraction (XRPD) including in situ XRPD characterisation upon thermal treatment. For the first time we have undoubtedly demonstrated, both theoretically and experimentally, the metastability of the corundum-type In2O3 polymorph. The In2O3 polymorph appears to be metastable throughout the entire enthalpy,pressure phase diagram. Upon heating, corundum-type In2O3 transforms irreversibly into cubic bixbyite-type In2O3 as shown by STA as well as in situ heating XRPD experiments. Computations indicate the existence of another high-pressure modification of In2O3 with orthorhombic structure, iso-typic to Rh2O3 -II. We predict this new phase to form at pressures exceeding 15,GPa from both the cubic bixbyite-type and the corundum-type modification of In2O3. [source] | ||||||||||||||||