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Monoclinic Structure (monoclinic + structure)
Selected AbstractsSynthesis, Mechanism, and Gas-Sensing Application of Surfactant Tailored Tungsten Oxide NanostructuresADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Suman Pokhrel Abstract Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, 1H, and 13C NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a,=,0.7297,nm, b,=,0.7539,nm, c,=,0.7688,nm, and ,-i;,=,90.91,°. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15,nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40,60,nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials. [source] Thermal dehydration kinetics of a rare earth hydroxide, Gd(OH)3INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2007Chengkang Chang This paper reports the synthesis, characterization, and dehydration kinetics of a rare earth hydroxide, Gd(OH)3. Uniform rod-like Gd(OH)3 powder was prepared by a colloidal hydrothermal method. The powder thus obtained dehydrated into its oxide form in a two-step process, where crystalline GdOOH was obtained as the intermediate phase. Crystal structure study revealed a monoclinic structure for GdOOH, with space group P2/1m and lattice parameters a = 6.0633, b = 3.7107, c = 4.3266, and , = 108.669. The first-step dehydration follows the F2 mechanism, while the second step follows the F1 model, indicating that both the steps are controlled by nucleation/growth mechanism. The activation energy Ea and frequency factor A are 231±12 kJ/mol and 2.08 × 1018 s,1 for the first step and 496 ± 32 kJ/mol and 7.88 × 1033 s,1 for the second step, respectively. Such high activation energy calculated from the experimental data can be ascribed to the high bonding energy of GdO bond, and the difference in activation energy for the two steps is due to the change in the bond length of hexagonal Gd(OH)3 and monoclinic GdOOH. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 75,81, 2007 [source] Thermodynamic Properties and Phase Diagram for the System MoO2,TiO2JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008K. Thomas Jacob The activity of molybdenum dioxide (MoO2) in the MoO2,TiO2 solid solutions was measured at 1600 K using a solid-state cell incorporating yttria-doped thoria as the electrolyte. For two compositions, the emf was also measured as a function of temperature. The cell was designed such that the emf is directly related to the activity of MoO2 in the solid solution. The results show monotonic variation of activity with composition, suggesting a complete range of solid solutions between the end members and the occurrence of MoO2 with a tetragonal structure at 1600 K. A large positive deviation from Raoult's law was found. Excess Gibbs energy of mixing is an asymmetric function of composition and can be represented by the subregular solution model of Hardy as follows The temperature dependence of the emf for two compositions is reasonably consistent with ideal entropy of mixing. A miscibility gap is indicated at a lower temperature with the critical point characterized by Tc (K)=1560 and. Recent studies indicate that MoO2 undergoes a transition from a monoclinic to tetragonal structure at 1533 K with a transition entropy of 9.91 J·(mol·K),1. The solid solubility of TiO2 with rutile structure in MoO2 with a monoclinic structure is negligible. These features give rise to a eutectoid reaction at 1412 K. The topology of the computed phase diagram differs significantly from that suggested by Pejryd. [source] Luminescence properties and growth of pure and anthracene-doped naphthalene crystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007N. Balamurugan Abstract Pure and anthracene-doped naphthalene crystals of high quality with 20 mm diameter and 60 mm length have been grown by the self-seeded vertical Bridgman method. The powder X-ray diffraction studies and the Raman analysis show that the guest molecules appear as defects in the form of irregularly oriented molecules that do not significantly distort the monoclinic structure. The absorbance and fluorescence studies show high Stoke's shift for anthracene-doped naphthalene crystals. From this we deduce that the exciting wavelength of the light (270 nm) is completely absorbed by the naphthalene, so that fluorescence from anthracene takes place as a result of energy transfer from naphthalene. The decay time observed for anthracene-doped naphthalene is 27 ± 2 ns. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase stability in ferroelectric bismuth titanate: a first-principles studyACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2008Anurag Shrinagar Experimental data on the structure of ferroelectric oxide bismuth titanate suggest two different kinds of structures, i.e. orthorhombic and monoclinic. Density-functional-theory-based (DFT) first-principles calculations have been performed to determine the most stable structure of bismuth titanate among experimentally observed structures. Orthorhombic and monoclinic phases are optimized to zero pressure and lattice parameters were determined as a = 5.4370, b = 5.4260, c = 32.6833,Å and Z = 4 for the structure with space group B2cb, and a = 5.4289, b = 5.4077, c = 32.8762,Å, , = 90.08° and Z = 4 for the structure with space group B1a1. Static and relaxation calculations show that the monoclinic structure with space group B1a1 is the most stable structure. [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] Pressure-induced polymorphism in phenolACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002David R. Allan The high-pressure crystal structure of phenol (C6H5OH), including the positions of the H atoms, has been determined using a combination of single-crystal X-ray diffraction techniques and ab initio density-functional calculations. It is found that at a pressure of 0.16,GPa, which is just sufficient to cause crystallization of a sample held at a temperature just above its ambient-pressure melting point (313,K), a previously unobserved monoclinic structure with P21 symmetry is formed. The structure is characterized by the formation of hydrogen-bonded molecular chains, and the molecules within each chain adopt a coplanar arrangement so that they are ordered in an alternating 1-1-1 sequence. Although the crystal structure of the ambient-pressure P1121 phase is also characterized by the formation of molecular chains, the molecules adopt an approximate threefold arrangement. A series of ab initio calculations indicates that the rearrangement of the molecules from helical to coplanar results in an energy difference of only 0.162,eV,molecule,1 (15.6,kJ,mole,1) at 0.16,GPa. The calculations also indicate that there is a slight increase in the dipole moment of the molecules, but, as the high-pressure phase has longer hydrogen-bond distances, it is found that, on average, the hydrogen bonds in the ambient-pressure phase are stronger. [source] X-ray structure determination of the monoclinic (121,K) and orthorhombic (85,K) phases of langbeinite-type dithallium dicadmium sulfateACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2000A. Guelylah The structures of the monoclinic and the orthorhombic phases of type I langbeinite Tl2Cd2(SO4)3 have been determined at 121 and 85,K, respectively, by X-ray diffraction. A precise analysis of these structures shows the existence of some differences compared to langbeinites of type II. The monoclinic structure differs very little from the high-temperature cubic structure and the distortion relating the monoclinic structure to the cubic one is very small. SO4 tetrahedra seem to rotate under orthorhombic symmetry in the monoclinic phase. A symmetry distortion analysis of the ferroelectric monoclinic distortion discloses the importance of the secondary modes with orthorhombic symmetry, especially for the O atoms of the SO4 groups. [source] Pseudomerohedrally twinned monoclinic structure of unfolded `free' nonactin: comparative analysis of its large conformational change upon encapsulation of alkali metal ionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Ilia A. Guzei The title compound, C40H64O12, crystallizes in a pseudomerohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-molecules of nonactin in the asymmetric unit. Each molecule has a pseudo- S4 symmetry and resides on a crystallographic twofold axis; the axes pass through the molecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nonactin as an order,disorder structure in an orthorhombic unit cell is corrected. We report a low-temperature high-precision ordered structure of `free' nonactin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4+ cations that exhibit more isometric overall conformations. [source] Three novel non-centrosymmetric compounds of glycine: glycine lithium sulfate, glycine nickel dichloride dihydrate and glycine zinc sulfate trihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2004Michel Fleck The crystal structures of three compounds of glycine and inorganic materials are presented and discussed. The orthorhombic structure of glycinesulfatodilithium(I), [Li2(SO4)(C2H5NO2)]n, consists of corrugated sheets of [LiO4] and [SO4] tetrahedra. The glycine molecules are located between these sheets. The main features of the monoclinic structure of diaquadichloroglycinenickel(II), [NiCl2(C2H5NO2)(H2O)2]n, are helical chains of [NiO4Cl2] octahedra connected by glycine molecules. The orthorhombic structure of triaquaglycinesulfatozinc(II), [Zn(SO4)(C2H5NO2)(H2O)3]n, is made up of [O3SOZnO5] clusters. These clusters are linked by glycine molecules into zigzag chains. All three compounds are examples of non-centrosymmetric glycine compounds. [source] Platinum-induced space-group transformation in crystals of the platelet glycoprotein Ib, N-terminal domainACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2004Kottayil I. Varughese The interaction between platelet glycoprotein (GP) Ib, and von Willebrand factor (VWF) is essential for thrombus formation, leading to the arrest of bleeding. The N-terminal domain of GP Ib,, which contains the binding sites for VWF and ,-thrombin, crystallized in the tetragonal space group P43 with one molecule in the asymmetric unit. When the crystals were treated with platinum, the crystals changed their symmetry from tetragonal to monoclinic P21 with two molecules in the asymmetric unit. The structure of the monoclinic form was solved using two-wavelength platinum anomalous dispersion data. The tetragonal crystal structure was subsequently solved using molecular-replacement techniques using the monoclinic structure as the search model and was refined with 1.7,Å resolution data. [source] Evidence of a phase transition of RbHCO3 from high-resolution solid-state 13C and 87Rb NMR by comparison with KHCO3MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2004Christophe Odin Abstract A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc , 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||