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Orthorhombic
Terms modified by Orthorhombic Selected AbstractsThickness-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] 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] The Room-Temperature Superstructure of ZrP2O7 Is Orthorhombic: There Are no Unusual 180° P,O,P Bond Angles.CHEMINFORM, Issue 33 2006Henrik Birkedal Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Neutron Powder Diffraction Study of the Orthorhombic to Monoclinic Transition in Sc2W3O12 on Compression.CHEMINFORM, Issue 25 2006Tamas Varga Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis, crystal structure and vibrational characterization of bis-,-peroxo-hexacarbonatodicerate(IV) complexes of rubidium and cesiumCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008N.-P. Pook Abstract The new compounds Rb8[Ce(O2)(CO3)3]2 · 12 H2O (1) and Cs8[Ce(O2)(CO3)3]2 · 10 H2O (2) were obtained from the reaction of hydrogen peroxide and Ce(III) in saturated alkali carbonate solutions. The crystal structures and the unit cell parameters of (1) triclinic, P-1 with a = 8.973(2) Å, b = 10.815(2) Å, c = 11.130(3) Å, , = 66.992(2)°, , = 68.337(2)°, , = 74.639(2)°, VEZ = 914.7(4) Å3, Z = 2, and (2) orthorhombic, Pbca, a = 19.3840(16) Å, b = 18.528(2) Å, c = 10.487(3) Å, VEZ = 3766.4(13) Å3, Z = 8, were determined. Both compounds contain the bis-µ-peroxo-hexacarbonatodicerate(IV)-ion, [(CO3)3Ce(O2)2Ce(CO3)3]8- . IR and Raman spectra were measured and discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hafnium Oxide Doped Mesostructured Silica FilmsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Ralf Supplit Abstract Hafnium oxide doped silica films with ordered mesostructures were produced with hafnium:silicon ratios between 1:60 and 1:6. A surfactant,hafnium alkoxide complex was synthesized and used as a template in a sol,gel dip-coating process. Face-centred orthorhombic, 2D centred rectangular and lamellar films were formed by evaporation-induced self-assembly (EISA). The influence of subsequent heat treatment was studied by GISAXS and TEM. The surface and in-depth molecular composition of the films was studied by XPS.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Structural and Electrochemical Studies of Dimerization and Rotational Isomerization in Multi-Iron SilicotungstatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005Travis M. Anderson Abstract A structural and electrochemical investigation of dimerization and Baker,Figgis (rotational) isomerization in the tri-ferric-substituted silicotungstates has been undertaken because these phenomena are important in a large number of polyoxometalates. A single-crystal X-ray diffraction analysis of K4Na7[(,-SiFe3W9(OH)3O34)2(OH)3] (,1) has been carried out [a = 12.9709(7) Å, b = 38.720(2) Å, c = 21.4221(12) Å, orthorhombic, Pbcm, R1 = 8.48,%, based on 13809 independent reflections]. The complex is isostructural with [(,-SiFe3W9(OH)3O34)2(OH)3]11, (,1) except that the edge-shared W3O13 caps in each [SiFe3W9(OH)3O34]4, unit are rotated by 60°. Electrochemical measurements, performed in a pH 5 acetate buffer, indicate a positive shift in the FeIII -based peak potential (and no change for the WVI -based potential) upon going from ,1 to its monomeric derivative [(,-Si(FeOH2)3W9(OH)3O34)]4, (,2) (,0.484,±,0.005 V and ,0.474,±,0.005 V, respectively). In contrast, the peak potentials of the FeIII - and WVI -based redox processes of ,1 are both found at more negative values than its rotational isomer ,1. The absolute values of the reduction peak potential differences are 0.022 V for FeIII and 0.162 V for WVI. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Carboxy Ester Hydrolysis Promoted by a Dicopper(II) Macrocyclic Polyamine Complex with Hydroxypropyl Pendant GroupsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2004Jin Huang Abstract A dinuclear CuII complex containing a hexaaza macrocyclic ligand bearing two 2-hydroxypropyl pendants, 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxypropyl)tricyclo[22.2.2.211,14]triaconta-1,11,13,24,27,29-hexaene (L), was synthesized. The title complex [Cu2(H,2L)Cl2]·6.5H2O was isolated as a blue crystal, orthorhombic, space group Fddd, with a = 16.4581(12), b = 32.248(2), c = 35.830(2) Å, V = 19017(2) Å3, Z = 16, R1 = 0.0690, and wR2 = 0.1546 [I > 2,(I)]. The protonation constants of Cu2L were determined by potentiometric titration, and it was found that the alcoholic hydroxypropyl group of the complex Cu2L exhibits low pKa values of pKa1 = 7.31, pKa2 = 7.83 at 25 °C. The hydrolysis kinetics of 4-nitrophenyl acetate (NA) promoted by the title complex have also been studied. The pH-rate profile for Cu2L gave a sigmoidal curve and showed a second-order rate constant of 0.39 ± 0.02 M,1 s,1 in 10% CH3CN/H2O(v/v), which is greater than that of the dinuclear CuII complex formed by a hexaaza macrocycle without pendants. The reason for the higher catalytic activity of the title complex is discussed. We found that the volume of nucleophile RO, can effect the hydrolysis of the carboxy ester, the nucleophilicity of RO, and the Lewis acidity of the metal macrocycle also affect the carboxy ester hydrolysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] In situ Investigation of Structural Changes during Deformation and Fracture of Polymers by Synchrotron SAXS and WAXS,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Konrad Schneider By simultaneous mechanical characterisation and synchrotron wide-angle x-ray scattering (WAXS) and small-angle x-ray scattering (SAXS), it is possible to characterise on-line local changes in a polymer's structure with a rather-high time and space resolution, together with the mechanical properties. In this contribution, we discuss the experimental requirements for such investigations as well as three examples. The evolution of structural features during tensile deformation of a polyethylene copolymer, as depicted by WAXS (top) and SAXS (bottom) are shown in the figure. The deformation leads to a martensitic transformation from the orthorhombic to monoclinic system and the formation of nanocavities. [source] Surface waves in a general anisotropic poroelastic solid half-spaceGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004M. D. Sharma SUMMARY A method is introduced for studying surface waves in a general anisotropic poroelastic medium. The method is analogous to the one used for isotropic media and derives a complex secular equation to represent the propagation of surface waves at the stress-free plane surface of a non-dissipative porous medium. The point of importance is that the derived equation is, analytically, separable into real and imaginary parts and hence can be solved by iterative numerical methods. A root of this secular equation represents the existence of surface waves and calculates the apparent phase velocity along a given direction on the surface. Numerical work is carried out for the model of a crustal rock. The propagation of surface waves is studied numerically for the top three anisotropies (i.e. triclinic, monoclinic, orthorhombic). [source] Vertically fractured transversely isotropic media: dimensionality and deconstructionGEOPHYSICAL PROSPECTING, Issue 2 2009Michael A. Schoenberg ABSTRACT A vertically fractured transversely isotropic (VFTI) elastic medium is one in which any number of sets of vertical aligned fractures (each set has its normal lying in the horizontal x1, x2 -plane) pervade the medium and the sets of aligned fractures are the only features of the medium disturbing the axi-symmetry about the x3 -axis implying that in the absence of fractures, the background medium is transversely isotropic (TI). Under the assumptions of long wavelength equivalent medium theory, the compliance matrix of a fractured medium is the sum of the background medium's compliance matrix and a fracture compliance matrix. For sets of parallel rotationally symmetric fractures (on average), the fracture compliance matrix is dependent on 3 parameters , its normal and tangential compliance and its strike direction. When one fracture set is present, the medium is orthorhombic and the analysis is straightforward. When two (non-orthogonal) or more sets are present, the overall medium is in general elastically monoclinic; its compliance tensor components are subject to two equalities yielding an 11 parameter monoclinic medium. Constructing a monoclinic VFTI medium with n embedded vertical fracture sets, requires 5 TI parameters plus 3×n fracture set parameters. A deconstruction of such an 11 parameter monoclinic medium involves using its compliance tensor to find a background transversely isotropic medium and several sets of vertical fractures which, in the long wavelength limit, will behave exactly as the original 11 parameter monoclinic medium. A minimal deconstruction, would be to determine, from the 11 independent components, the transversely isotropic background (5 parameters) and two fracture sets (specified by 2 × 3 = 6 parameters). Two of the background TI medium's compliance matrix components are known immediately by inspection, leaving nine monoclinic components to be used in the minimal deconstruction of the VFTI medium. The use of the properties of a TI medium, which are linear relations on its compliance components, allows the deconstruction to be reduced to solving a pair of non-linear equations on the orientations of two fracture sets. A single root yielding a physically meaningful minimum deconstruction yields a unique minimal representation of the monoclinic medium as a VFTI medium. When no such root exists, deconstruction requires an additional fracture set and uniqueness is lost. The boundary between those monoclinic media that have a unique minimal representation and those that do not is yet to be determined. [source] A Chemical Route to BiNbO4 CeramicsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2009Oleg A. Shlyakhtin The liquid phase sintering of fine BiNbO4 powders allows to obtain dense ceramics with excellent microwave dielectric properties (,=44,46; Q×f=16,500,21,600 GHz) at T,700°C. The thermal decomposition of freeze-dried precursors results in the crystallization of a metastable ,,-BiNbO4 polymorph that transforms into a stable orthorhombic ,-modification at T,700°C. The dependence of sinterability on the powder synthesis temperature shows the maximum at 600°C, corresponding to the formation of crystalline BiNbO4 powders with a grain size 80,100 nm. Sintering temperature reduction to 700°C prevents the deterioration of silver contacts during co-firing with BiNbO4 ceramics. In situ scanning electron microscopy observation of the morphological evolution during sintering shows that the intense shrinkage soon after the appearance of a CuO,V2O5 eutectics-based liquid phase is accompanied by complete transformation of the ensemble of primary BiNbO4 particles. [source] Low-temperature phase transformation and phonon confinement in one-dimensional Ta2O5 nanorodsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010Rupesh S. Devan The thermochromic phase transformations of one-dimensional Ta2O5 nanorods have been analyzed at elevated temperatures ranging from 80 to 300,K. The nanorods, grown in a large-area high-density array, are 14,22,nm wide and approximately 500,nm long. The array contained ,93.5% of the orthorhombic (,) phase and ,6.5% of the tetragonal (,) phase. Low-temperature X-ray diffraction results showed complex and polymorphic thermochromic phase transformations of the ,(001), ,(101) and ,(103) lattice planes of the nanorods, which incorporate (i) ,-to-, (,,,), (ii) ,,,,, and (iii) ,,, phase transitions. In comparison with the Raman scattering of three-dimensional bulk powder and two-dimensional thin films of Ta2O5, there were concurrent Raman blue- and redshifts in the one-dimensional Ta2O5 nanorods, indicating that the molecular vibrations of the nanorods were confined owing to the reduction of size and dimension. [source] The crystal structure of perdeuterated methanol hemiammoniate (CD3OD·0.5ND3) determined from neutron powder diffraction data at 4.2 and 180,KJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010A. D. Fortes The crystal structure of perdeuterated methanol hemiammoniate, CD3OD·0.5ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180,K. The structure is orthorhombic, space group Pn21a (Z = 4), with unit-cell dimensions a = 12.70615,(16), b = 8.84589,(9), c = 4.73876,(4),Å, V = 532.623,(8),Å3 [,calc = 1149.57,(2),kg,m,3] at 4.2,K, and a = 12.90413,(16), b = 8.96975,(8), c = 4.79198,(4),Å, V = 554.656,(7),Å3 [,calc = 1103.90,(1),kg,m,3] at 180,K. The crystal structure was determined by ab initio methods from the powder data; atomic coordinates and isotropic displacement parameters were subsequently refined by the Rietveld method to Rp, 2% at both temperatures. The crystal structure comprises a three-dimensionally hydrogen-bonded network in which the ND3 molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule. This connectivity leads to the formation of zigzag chains of ammonia,hydroxy groups extending along the c axis, formed via N,D···O hydrogen bonds; these chains are cross-linked along the a axis through the hydroxy moiety of the second methanol molecule via N,D···O and O,D···O hydrogen bonds. This `bridging' hydroxy group in turn donates an O,D···N hydrogen bond to ammonia in adjacent chains stacked along the b axis. The methyl deuterons in methanol hemiammoniate, unlike those in methanol monoammoniate, do not participate in hydrogen bonding and reveal evidence of orientational disorder at 180,K. The relative volume change on warming from 4.2 to 180,K, ,V/V, is + 4.14%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths, e.g.,a/a) than, that observed in deuterated methanol monohydrate, and very similar to what is observed in methanol monoammoniate. [source] High-pressure properties of TiP2O7, ZrP2O7 and ZrV2O7JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2001Stefan Carlson High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38,1.58,GPa from cubic ,- to pseudo-tetragonal ,-ZrV2O7 that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4,GPa, ZrV2O7 becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7 and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5,GPa, respectively). These differences in high-pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, ,-ZrV2O7 and ,-ZrV2O7 were estimated to be 42,(3), 39,(1), 17.0,(7) and 20.8,(10),GPa, respectively. [source] Conformational polymorphism in aripiprazole: Preparation, stability and structure of five modificationsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2009Doris E. Braun Abstract Five phase-pure modifications of the antipsychotic drug aripiprazole were prepared and characterized by thermal analysis, vibrational spectroscopy and X-ray diffractometry. All modifications can be produced from solvents, form I additionally by heating of form X° to ,120°C (solid,solid transformation) and form III by crystallization from the melt. Thermodynamic relationships between the polymorphs were evaluated on the basis of thermochemical data and visualized in a semi-schematic energy/temperature diagram. At least six of the ten polymorphic pairs are enantiotropically and two monotropically related. Form X° is the thermodynamically stable modification at 20°C, form II is stable in a window from about 62,77°C, and form I above 80°C (high-temperature form). Forms III and IV are triclinic (), I and X° are monoclinic (P21) and form II orthorhombic (Pna21). Each polymorph exhibits a distinct molecular conformation, and there are two fundamental N,HO hydrogen bond synthons (catemers and dimers). Hirshfeld surface analysis was employed to display differences in intermolecular short contacts. A high kinetic stability was observed for three metastable polymorphs which can be categorized as suitable candidates for the development of solid dosage forms. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2010,2026, 2009 [source] Phonon properties of nanosized bismuth layered ferroelectric material,Bi2WO6JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010M. Ma Abstract Nanosized Bi2WO6 was synthesized by a mild hydrothermal crystallization process. This method allowed obtaining plate-like crystallites of very small thickness (down to 3 nm). The effect of particle size on the structure and properties of Bi2WO6 was studied by X-ray diffraction (XRD), transmission electron microscopy, and Raman and infrared spectroscopies. It has been shown that the orthorhombic distortion decreases with decreasing particle size, but the structure of the smallest crystallites is still orthorhombic. Raman studies have also revealed a very strong intensity decrease for those modes that appear mainly for incident and scattered light polarized perpendicular to the layers. This behavior has been attributed to a decrease in the orthorhombic distortion and a plate-like shape of the nanocrystallites. Copyright © 2009 John Wiley & Sons, Ltd. [source] Structural phase transition in [NH3(CH2)5NH3]BiCl5: thermal and vibrational studiesJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2005H. Jeghnou Abstract An x-ray diffraction study carried out on the pentylenediammonium pentachlorobismuthate (III) compound [NH3(CH2)5NH3]BiCl5 indicated that it is orthorhombic with a P212121(Z = 4) space group. Differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were also made, which showed that this compound undergoes a unique phase transition at high temperatures. The infrared and Raman spectra recorded at room temperature were interpreted on the basis of data published in the literature. The Raman bands observed below 300 cm,1 are very characteristic of the anions, which are made of isolated (BiCl52, )n units composed of BiCl63, octahedra. Raman spectra recorded at various temperatures confirmed the contribution to the phase-transition mechanism of both the anion and cation motions. Copyright © 2005 John Wiley & Sons, Ltd. [source] Crystal structure and polarized vibrational spectra of 2-bromo-4-nitropyridine N -oxide single crystalJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2002J. Hanuza 2-Bromo-4-nitropyridine N -oxide is orthorhombic, space group Pbca, with eight molecules per unit cell of dimensions a = 5.979(1), b = 9.899(1), c = 23.249(5) Å. The Br ion is nearly coplanar with the pyridine ring, while the two oxygen atoms of the nitro group are displaced above and below the ring by (,0.214 Å) and (+0.053 Å). The hydrogen bond of the type C,H···O links the molecules into pairs around centers of symmetry. These dimers, arranged into layers related by glide planes, are held together solely by contacts of the van der Waals type. The polarized Fourier transform IR and Raman spectra, measured in the regions 30,3500 and 80,3500 cm,1, respectively, are correlated with x-ray structural data. Comparison of the spectrum of the dissolved sample with the spectra obtained from the polycrystalline sample and single crystals shows the attractive character of the intermolecular C,H···O contacts for these molecules. The temperature-dependent IR spectra suggest the presence of orientational disorder at higher temperatures. Copyright © 2002 John Wiley & Sons, Ltd. [source] Raman phonons and Raman Jahn,Teller bands in perovskite-like manganitesJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2001Milko N. Iliev The perovskite-like manganites R1,xAxMnO3, where R is a trivalent rare earth or Y and A is a divalent alkaline earth element, are characterized by a strong interplay of magnetism, electric transport and crystallographic distortion. At doping levels 0.15 < x < 0.45 the materials exhibit colossal magnetoresistance near the concomitant ferromagnetic and insulator,metal transitions. At a fractional doping level, such as x = 0.5, the crystallographic and magnetic environment is strongly modified and charge ordering between Mn3+ and Mn4+ or phase separation takes place. In this work, the polarized Raman spectra of the orthorhombic and rhombohedral phases of parent RMnO3 compound were analyzed in close comparison with results of lattice dynamic calculations. We argue that the strong high-wavenumber bands between 400 and 700 cm,1, which dominate the Raman spectra of rhombohedral RMnO3 and magnetoresistive La1,xAxMnO3 are not proper Raman modes for the R3c or Pnma structures. Rather, the bands are of phonon density-of-states origin and correspond to oxygen phonon branches activated by the non-coherent Jahn,Teller distortions of the Mn3+O6 octahedra. The reduction of these bands upon doping of La1,xAxMnO3 and their disappearance in the ferromagnetic metallic phase support the model. The variation with temperature of the Raman spectra of La0.5Ca0.5MnO3 is also discussed. The results give a strong indication for charge and orbital ordering and formation of superstructure at low temperatures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electrode Properties of the Ruddlesden,Popper Series, Lan+1NinO3n+1 (n=1, 2, and 3), as Intermediate-Temperature Solid Oxide Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Suguru Takahashi The Ruddlesden,Popper phases, Lan+1NinO3n+1 (n=1, 2, and 3), were synthesized by a solid-state reaction for use as cathodes in an intermediate-temperature (500°,700°C) solid oxide fuel cell. The samples crystallized into an orthorhombic layered perovskite structure. The overall electrical conductivity increased with the increase of n in the intermediate temperature range. Single test-cells, which consisted of samarium-oxide-doped ceria (SDC; Sm0.2Ce0.8Ox) as an electrolyte, Ni,SDC cermet (Ni,SDC) as an anode, and Lan+1NinO3n+1 as a cathode, were fabricated for measurements of cell performance at 500°,700°C. Current interruption measurements revealed that both the ohmic and overpotential losses at 700°C decreased with the increase of n. La4Ni3O10 was found to exhibit the best cathode characteristics in the Lan+1NinO3n+1 series. Maximum test-cell power densities with La4Ni3O10 (n=3) were 10.2, 36.5, and 88.2 mW/cm2 at 500°, 600°, and 700°C, respectively. [source] Effects of Poling Process on KNN-Modified Piezoceramic PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010F. Rubio-Marcos The influence of the orthorhombic to tetragonal phase transition near room temperature in the poling process of KNN-modified piezoceramics was studied. Poling temperatures of 25° and 120°C were used. The percentage of 90° domains reorientation induced by poling was evaluated trough X-ray diffraction analysis. The improvement of the piezoelectric properties when the poling temperature was 25°C could not be explained by the reorientation of 90° domains alone. Raman spectroscopy evidenced that the polarization process was assisted by the stabilization of orthorhombic phase, which promotes a stress reduction in the material. [source] Effect of BiScO3 and LiNbO3 on the Piezoelectric Properties of (Na0.5K0.5)NbO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Xueyi Sun Lead-free potassium sodium niobate-based piezoelectric ceramics (1,y)(Na0.5,0.5xK0.5,0.5xLix)NbO3,yBiScO3 ( y=0.01, x=0,0.06) have been prepared by an ordinary sintering process. The XRD analysis showed that the structure changes from orthorhombic to tetragonal with the increase of x (at y=0.01, abbreviated as KNNBSL100x). At room temperature, the polymorphic phase transition from the orthorhombic to the tetragonal phase was identified at approximately 0.02,x,0.04. The piezoelectric and ferroelectric properties were significantly enhanced. The temperature dependences of the relative permittivity revealed that the Curie temperature was increased with the addition of LiNbO3. These solid solution ceramics are promising as potential lead-free candidate materials. [source] Synthesis of a Biomorphic Molybdenum Trioxide Templated from PaperJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Jia Li A biomorphic ,-MoO3 ceramic was successfully derived from paper templates. By the infiltration of a Mo-contained solution into paper templates, followed by calcinations at 500°C in air, the cellulose fibers of paper were converted into branches composing of orthorhombic ,-MoO3 crystals with grain size ranging from 0.5 to 2 ,m. In the final product, the initial fibrous structure of the paper templates was retained. This simple biotemplate method provides a cost-effective and ecofriendly route to obtain advanced self-assembling biomorphic ceramics. [source] Phase Evolution During Formation of SrAl2O4 from SrCO3 and ,-Al2O3/AlOOHJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Yu-Lun Chang Through the execution of experimental investigation, thermogravimetry, X-ray diffractometry, Fourier transform-infrared spectrometry, transmission electron microscopy, and energy-dispersive spectrometry, a variant reaction mechanism model was proposed for the solid-state reaction between SrCO3 and Al2O3/AlOOH for formation of SrAl2O4 material. The solid-state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO3 from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO3 and alumina. Conversely, at temperatures higher than that, the solid-state reaction is dominated by the diffusion of Al3+ ions into the SrCO3 lattice. In this mechanism, two metastable species, hexagonal SrCO3 and hexagonal SrAl2O4, were observed. The activation energies of SrCO3 decomposition in the solid-state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ,130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO3 decomposition decreases to 34 kJ/mol. [source] Phase Transition and Failure at High Temperature of Bismuth-Layered Piezoelectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Liaoying Zheng High-temperature bismuth-layered piezoelectric ceramics (CaxSr1,x)Bi4Ti4O15 have been prepared by the conventional solid reaction method. Our results reveal that there is a "phase transition induced by the composition" taking place in the solid solution at around x=0.4. During transition, the crystal structure changes from orthorhombic to pseudo-tetragonal and then back to orthorhombic. Although all (CaxSr1,x)Bi4Ti4O15 (with any x value) undergo a second-order ferroelectric-to-ferroelectric phase transition at about 200°C below their Curie temperature, only the ceramic with x=0.4 exhibits a failure in piezoelectric properties during the transition. It is suggested that, on the basis of the X-ray photoelectron spectroscopy results, this material failure is induced by the high concentration of oxygen vacancies in the material during the phase transition. [source] Thermodynamic and Structural Properties of Sodium Lithium Niobate Solid SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Irina Pozdnyakova Thermodynamics of the Na1,xLixNbO3 system is investigated by high-temperature drop-solution calorimetry in molten 3Na2O,4MoO3 solvent at 973 K. Standard molar enthalpies of formation are derived. The estimated heats of transition between hypothetical and stable structures, lithium niobate and perovskite for NaNbO3 and vice versa for LiNbO3 are ,6 kJ/mol and ,10 kJ/mol, respectively. X-ray diffraction studies at room temperature showed for 0 ,x, 0.14 there are three phases based on different ordering of the perovskite type lattice: orthorhombic with a quadrupled reduced perovskite cell at 0 ,x, 0.02, orthorhombic with a doubled reduced perovskite cell at 0.015 ,x, 0.14, and rhombohedral at 0.08 ,x, 0.13. There are two two-phase (morphotropic) regions with coexistence of the two orthorhombic phases at 0.015 ,x, 0.02 and with the second orthorhombic phase coexisting with the rhombohedral phase at 0.08 ,x, 0.13. A reproducible anomaly in specific heat at ,600 K, not reported previously, has been observed in pure NaNbO3. Heat-capacity measurements confirm a phase transition at 553 K for 0.07 ,x, 0.09. With increasing lithium concentration, a gradual disappearance of high-temperature phase transitions associated with tilting of oxygen octahedra has been observed. [source] Effect of MgO Doping on the Phase Transformations of BaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Toru Nagai The successive phase transformations in MgO-doped BaTiO3 were studied. Upon MgO doping, dielectric anomalies corresponding to lower phase transformations were broadened and depressed, while an anomaly for a cubic,tetragonal transformation remained and shifted to a lower temperature. XRD peak splitting upon tetragonality of BaTiO3 was decreased, and the peaks exhibited abnormally broadened profiles which are different from the one for cubic BaTiO3 above Tc. Raman spectroscopy revealed the existence of orthorhombic phase at room temperature for the solid solution with 0.5 mol% or more MgO. The temperature dependence of the Raman spectrum showed that orthorhombic and rhombohedral phases in MgO-doped BaTiO3 were stabilized at higher temperatures than pure BaTiO3. [source] Microstructure and electrical properties of (1,x)(K0.5Na0.5)NbO3,x BiFeO3 piezoelectric ceramicsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008Xiang Li Abstract Lead,free ceramics (1,x)(K0.5Na0.5)NbO3,x BiFeO3 doped with 1 mol% Fe2O3 (KNNBF/x) have been synthesized by pressureless sintering. With the Fe2O3 doping, the KNNBF/x ceramics can be well sintered at 1085,1100 °C and exhibit a pure perovskite structure with x < 0.013. It was found that the crystal structure of the KNNBF/x ceramics changed from orthorhombic to tetragonal and then to pseudocubic phase with the increase of BiFeO3 content. The composition KNNBF/0.013 near the tetragonal symmetry that separates the orthorhombic and pseudocubic phases exhibits improved electrical properties: d33 = 173 pC/N, kp = 0.40, ,r = 905, tan , = 4%, Pr = 26 ,C/cm2, and Ec = 11.2 kV/cm, with a high Curie temperature (TC) of about 388 °C. Our results suggest that KNNBF/x are promising lead-free high temperature piezoelectric ceramics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Changes in optical properties of MnAs thin films on GaAs(001) induced by ,- to ,-phase transitionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008B. Gallas Abstract MnAs layers with 45 nm thickness were grown epitaxially on GaAs(001) substrates. Ellipsometry measurements were made in the spectral range 0.045 eV to 6 eV as a function of temperature (between ,10 °C and 50 °C) at 70° of incidence. In this way the transition from the hexagonal ,-phase to the orthorhombic ,-phase could be monitored. Non-zero off-diagonal elements of the Jones matrix for an azimuth of 38° off the [10] axis of the substrate indicate that the optical functions of MnAs are anisotropic in both phases. The optical conductivity exhibits low-energy interband transitions around 0.3 eV, more clearly seen in the ,-phase than in the ,-phase. Extrapolation of the optical conductivity to zero frequency confirms that the ,-phase is about two times more conducting than the ,-phase. A broad structure is observed in the visible range around 3 eV. The ,-phase is characterised by an anisotropy induced energy difference of this structure with a maximum at 2.8 eV for the extraordinary index and at 3.15 eV for the ordinary index. This difference vanishes in the ,-phase in which anisotropy mainly induces changes in amplitude of the 3 eV structure. The assignment of the structures will be discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||