Distortion Of Crystal Structure Research Articles

Homologous distortion of the aluminum crystal structure under laser radiation

It was shown by X-ray diffraction that the aluminum crystal structure is distorted under conditions of nonequilibrium laser heating, which appears in lowering the lattice symmetry. A method for describing the observed distortions, based on the transition to a new unit cell, was proposed. It was shown that the distorted aluminum crystal structure can be described using the transition from the face-centered cubic cell to the monoclinic body-centered cell. The parameters of the aluminum unit cell after laser irradiation were determined as a = 0.2870 nm, b = 0.2860 nm, c = 0.4060 nm, and β = 90.013° (for the axes of the monoclinic body-centered lattice).

The static and hyper-frequency magnetic properties of a ferromagnetic–ferroelectric composite

This paper reports the static and hyper-frequency magnetic properties, as well as their relationship with microstructure, of the ferromagnetic–ferroelectric co-fired composite ceramic, (1− x)Ba 2Zn 1.2Cu 0.8Fe 12O 22– xPb(Ni 1/3Nb 2/3) 0.8Ti 0.2O 3. The X-ray diffraction results did not detect any other phase in the co-fired ceramics, but found a crystal structural distortion of ferrite phase. Scanning electron microscopy photos showed that two phases’ grains matched well and stacked compactly and the hexagonal ferrite changed its grain morphology. The saturation magnetization increased with the reduction of magnetic phase in the range of 0< x<0.65 because of the stress-induced structural distortion. The permeability decreases monotonically with the reduction of magnetic phase in the whole composition range.

Modifying the oxygen adsorption properties of YBaCo4O7 by Ca, Al, and Fe doping

The doping effect of Ca, Al, and Fe on the oxygen adsorption properties of YBaCo4O7 was investigated by thermogravimetry (TG) method. It was found that the original YBaCo4O7 oxygen adsorption properties can be modified greatly by Ca, Al, and Fe doping. Ca doping in Y sites eliminates the oxygen adsorption at low temperature (~300 °C) but the oxygen adsorption properties at high temperature is almost unchanged. Minor Al doping in Co sites eliminates the oxygen adsorption hump at high temperature, but the hump at low temperature is preserved. Fe appearance in YBaCo3Al1−xFexO7 seems to weaken the effect of Al doping, so the oxygen hump at high temperature emerges again. The doping effect was discussed based on elements valence, binding energy between cations and oxygen ions, and distortion of crystal structure.

Molecular Interactions Alter Clay and Polymer Structure in Polymer Clay Nanocomposites

In this work, using photoacoustic Fourier transform infrared spectroscopy (FTIR) we have studied the structural distortion of clay crystal structure in organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCN). To study the effect of organic modifiers on the distortion of crystal structure of clay, we have synthesized OMMTs and PCNs containing same polymer and clay but with three different organic modifiers (12-aminolauric acid, n-dodecylamine, and 1,12-diaminododecane), and conducted the FTIR study on these PCNs. Our previous molecular dynamics (MD) study on these PCNs reveals that significant nonbonded interactions (van der Waals, electrostatic interactions) exist between the different constituents (polymer, organic modifier, and clay) of nanocomposites. Previous work based on X-ray diffraction (XRD) and differential scanning calorimetry (DSC) on the same set of PCNs shows that crystallinity of polymer in PCNs have changed significantly in comparison to those in pristine polymer; and, the nonbonded interactions between different constituents of PCN are responsible for the change in crystal structure of polymer in PCN. In this work to evaluate the structural distortion of crystal structure of clay in OMMTs and PCNs, the positions of bands corresponding to different modes of vibration of Si—O bonds are determined from the deconvolution of broad Si—O bands in OMMTs and PCNs obtained from FTIR spectra. Intensity and area under the Si—O bands are indicative of orientation of clay crystal structures in OMMTs and PCNs. Significant changes in the Si—O bands are observed from each vibration mode in OMMTs and PCNs containing three different organic modifiers indicating that organic modifiers influence the structural orientation of silica tetrahedra in OMMTs and PCNs. Deconvolution of Si—O bands in OMMTs indicate a band at ∼1200 cm−1 that is orientation-dependent Si—O band. The specific changes in intensity and area under this band for OMMTs with three different organic modifiers further confirm the change in structural orientation of silica tetrahedra of OMMTs by organic modifiers. Thus, from our work it is evident that organic modifiers have significant influence on the structure of polymer and clay in PCNs. It appears that in nanocomposites, in addition to strong interactions at interfaces between constituents, the structure of different phases (clay and polymer) of PCN are also altered, which does not occur in conventional composite materials. Thus, the mechanisms governing composite action in nanocomposites are quite different from that of conventional macro composites.

SWNT-DNA and SWNT-polyC Hybrids: AFM Study and Computer Modeling

In this work, using photoacoustic Fourier transform infrared spectroscopy (FTIR) we have studied the structural distortion of clay crystal structure in organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCN). To study the effect of organic modifiers on the distortion of crystal structure of clay, we have synthesized OMMTs and PCNs containing same polymer and clay but with three different organic modifiers (12-aminolauric acid, n-dodecylamine, and 1,12-diaminododecane), and conducted the FTIR study on these PCNs. Our previous molecular dynamics (MD) study on these PCNs reveals that significant nonbonded interactions (van der Waals, electrostatic interactions) exist between the different constituents (polymer, organic modifier, and clay) of nanocomposites. Previous work based on X-ray diffraction (XRD) and differential scanning calorimetry (DSC) on the same set of PCNs shows that crystallinity of polymer in PCNs have changed significantly in comparison to those in pristine polymer; and, the nonbonded interactions between different constituents of PCN are responsible for the change in crystal structure of polymer in PCN. In this work to evaluate the structural distortion of crystal structure of clay in OMMTs and PCNs, the positions of bands corresponding to different modes of vibration of Si-O bonds are determined from the deconvolution of broad Si-O bands in OMMTs and PCNs obtained from FTIR spectra. Intensity and area under the Si-O bands are indicative of orientation of clay crystal structures in OMMTs and PCNs. Significant changes in the Si-O bands are observed from each vibration mode in OMMTs and PCNs containing three different organic modifiers indicating that organic modifiers influence the structural orientation of silica tetrahedra in OMMTs and PCNs. Deconvolution of Si-O bands in OMMTs indicate a band at approximately 1200 cm(-1) that is orientation-dependent Si-O band. The specific changes in intensity and area under this band for OMMTs with three different organic modifiers further confirm the change in structural orientation of silica tetrahedra of OMMTs by organic modifiers. Thus, from our work it is evident that organic modifiers have significant influence on the structure of polymer and clay in PCNs. It appears that in nanocomposites, in addition to strong interactions at interfaces between constituents, the structure of different phases (clay and polymer) of PCN are also altered, which does not occur in conventional composite materials. Thus, the mechanisms governing composite action in nanocomposites are quite different from that of conventional macro composites.

Temperature Raman scattering study of CaAl 0.5Ta 0.5O 3 perovskite crystal

Temperature Raman scattering studies were performed for CaAl 0.5Ta 0.5O 3 crystal. This material features NaCl-type ordering of Al 3+ and Ta 5+ ions at the B-site superimposed onto b − b − c + octahedral tilting. Because of the existing twin-related domains in crystal structure, the micro-Raman measurements were carried out at room temperature. Some differences in Raman spectra obtained using macro- and micro-Raman system were revealed. Most of the Raman modes show monotonous red-shift with the increase in temperature. Only the cubic-like fully symmetric A 1g mode slightly increases its frequency with an increase in temperature. There are no uncontinuous changes of mode frequency in the temperature range studied. It indicates the stable character of static distortions of crystal structure relying on changes of octahedra tilt angle.

Preparation of fine Mg1−XCaXFe2O4 powder using reverse coprecipitation method for thermal coagulation therapy in an ac magnetic field

Abstract New magnetic materials having a potentially high heat generation ability in an ac magnetic field were studied for application in thermal coagulation therapy. The Mg 1− X Ca X Fe 2 O 4 ferrites with X varied from 0 to 1.0 were synthesized using a reverse coprecipitation method. The obtained precursors were calcined at various temperatures in the range of 300–1000 °C with the intent to obtain fine ferrite powders. The heat generation in an ac magnetic field was very poor for X = 0. However, the heat generation improved with partial Ca 2+ substitution of the Mg 2+ sites. The maximum rise in temperature (Δ T ) in the ac magnetic field (370 kHz, 1.77 kA/m) was ca. 50 °C for the samples with 1.0 g in weight and 0.2–0.8 in X of Mg 1− X Ca X Fe 2 O 4 . Especially, the samples calcined at 800 °C showed the highest heat generation. When the Ca 2+ -substituted samples were calcined at 900 °C, the heat generation was reduced due to decomposition into the two phases of the MgFe 2 O 4 -type cubic and CaFe 2 O 4 -type orthorhombic. In addition, the samples calcined at 300 °C also showed a high heat generation. Although the crystal and particle sizes increased with the calcination temperature, they did not influence the heat generation of this system. The heat generation of the samples was closely related to the hysteresis loss. The reason for the high heat generation properties of the samples calcined at 300 and 800 °C is ascribed to the increase in the hysteresis loss by distortion of the cubic crystal structure.

Investigations of dielectric enhancement in (Ta2O5)1-x(TiO2)x ceramics prepared by laser-sintering technique

The maximum dielectric permittivity of Ti-doped Ta2O5 ceramics may reach 450 by a laser-sintering technique. The aim of this study is to investigate the mechanisms of the dielectric enhancement based on the unique structural and morphological properties of the laser-sintered ceramics. The reason for the dielectric enhancement is due to the crystal structure distortion in the high-temperature phase, the oriented grain growth taking place in a direction deviating from [001] in the laser-sintered ceramics. The concurrent nature of quenching effects, a sharp temperature gradient and mass transfer in liquid phase originated from laser high energy irradiation with strict directivity leads to the structural and morphological properties.

X‐ray diffraction study of low‐energy carbon‐ion implanted Si(001)

AbstractIn the search for Si‐ and C‐based crystalline phases in low‐energy ion implanted and electron‐beam annealed Si surface layers, X‐ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Thermoelectric Properties and Magnetic Anisotropies of Magnetically Grain-Oriented Sr- or Bi-doped Ca3Co4O9 Thick Films

AbstractWe report magnetic properties of [Ca2CoO3-δ]0.62CoO2 (Ca349) powders with various average size and the Bi- and Sr-doping effects on thermoelectric properties for the magnetically grain-aligned and densified Ca349 thick films. Magnetic anisotropy at 300 K depended on the initial average size of Ca349 powders and decreased with the decrease in the size. This presumably suggests that distortion of crystal structure was induced by a ball-milling process and led to the change of magnetic anisotropy. On the Bi- and Sr-doping effects, an obvious enhancement of thermoelectric properties did not emerge in the case of the Sr-doping, whereas the enhancement was observed for the Bi-doped Ca349 thick films. However, a drastic decrease of magnetic anisotropy was caused by the Bi-doping. For usage of the p-type layer in multilayered thermoelectric module, tuning of the Bi-doping levels in which both enhancement of thermoelectric properties and a certain level of magnetic anisotropy are achieved is required.

Surface free energy of copper-zinc alloy for energy-saving of boiler

Cu-Zn, Cu-Zn-Sn, Cu-Zn-Ni alloys were melted by vacuum smelter. The effect factors to the surface free energy of the alloys such as chemical composition, crystal structure and surface crystal lattice distortion etc. were investigated by OCA30 automatic contact angle test instrument, metallography microscope and XRD instrument etc. Results suggests: adding alloy element to Cu may increase its surface free energy, and the more kinds of alloy elements are added, the more surface free energy increases; the alloy element Sn an increase the surface free energy of Cu-Zn alloy; Cu-Zn alloy with fir-tree crystal structure, great phase discrepancy and obvious composition aliquation has greater surface free energy; Cu-Zn alloy with compounds and serious surface crystal lattice distortion has greater surface free energy.

Nano-structured Li2O from LiOH by electron-irradiation

Electron irradiation leads to a fast dissociation of larger grains of LiOH into nano-structured Li 2 O. In this Letter, an electron beam of a transmission electron microscope was employed to activate the in situ transformation of LiOH to Li 2 O. It was found that the electron irradiation (200 kV) leads to a fast dissociation of large grains of LiOH into nano-structured Li 2 O, as nano-fibers of about 20 nm diameter and nano-particles of 30 nm. This facile transformation is attributed to the combined effect of irradiation-induced distortion of LiOH crystal structure and heating by irradiation.

Effect of calcined temperature on the solubility of trace elements from Manifanshi

A medical stone manifanshi were researched by using polarized light microscopy, X-ray diffraction (XRD), and inductively coupled plasma atomic emission spectrometry (ICP-AES) methods. The XRD pattern of the raw Manifanshi indicates that it is daminantly composed of plagioclase, orthoclase, quartz, and that of the calcined Manifanshi at 1000°C shows that the distortion of crystal structure in both plagioclase and orthoclase takes place at the calcined temperature. The polarized light microscopy observation suggests that the Manifanshi is naturally weathered monzo-granite porphyry. Chemical analyses reveal that the Manifanshi contains a number of healthful trace elements and rare toxic trace elements, therefore, it is a high quality Manifanshi. The solubility of trace elements was determined by measuring the concentration of trace elements from Manifanshi calcined under varying temperature conditions by ICP method, the results suggest that the calcined product at 1000°C shows the ideal result in ionic concentrations and dissolution rate of trace elements in water, which is contributed to the distortion of the crystal structure of feldspar at the calcined temperature.

Crystal structure and high-field magnetism of La{sub 2}CuO{sub 4}

Neutron diffraction was used to determine the crystal structure and magnetic ordering pattern of a La{sub 2}CuO{sub 4} single crystal, with and without applied magnetic field. A previously unreported, subtle monoclinic distortion of the crystal structure away from the orthorhombic space group Bmab was detected. The distortion is also present in lightly Sr-doped crystals. A refinement of the crystal structure shows that the deviation from orthorhombic symmetry is predominantly determined to drive a continuous reorientation of the copper spins from the orthorhombic b axis to the c axis, directly confirming predictions based on prior magnetoresistance and Raman scattering experiments. A spin-flop transition induced by a c-axis oriented field previously reported for nonstoichiometric La{sub 2}CuO{sub 4} is also observed, but the transition field (11.5 T) is significantly larger than that in the previous work.

Typed-new multifunctional Mn-rich antiferromagnetic alloys

The lattice distortion of crystal structure can be formed and following fct martensitic transformation is induced with antiferromagnetic transition in Mn-rich antiferromagnetic alloys. The twin boundaries formed with fct martensitic transformation or tiny twin (antiferromagnetic domain boundaries) with antiferromagnetic transition have mobility and high damping property can be obtained under an alternate stress. With the help of the coupling between the second order antiferromagnetic transition and the first order martensitic transformation, the hysteresis between martensitic transformation and reversible one is decreased or even is disappeared, the martensitic transformation temperature, M s, and its reversible transformation temperature, A s, move closer to antiferromagnetic transition point, T n, the shape memory effect formed by martensitic transformation and its reversible one may be related with a simplex temperature function and a non-hysteresis on temperature can be formed. Because the tiny twin boundaries and the fct twin boundaries have movability under applied magnetic field, the magneto-driven strain and magneto-controlled shape memory effect may be shown. Now the new-typed multifunctional antiferromagnetic materials are being researched and developed in theoretically and practically.

An electrical field-induced structural effect in strontium titanate at room temperature

An electric field-induced reversible structural distortion at room temperature is observed at an as-cut single-crystalline SrTiO3 [001] wafer. The structural changes have been characterised in situ by means of X-ray diffraction. It is concluded that the effect requires a distortion of the cubic crystal structure, as it was present only at the rough unpolished side of the wafer. The appearance of the phenomenon was found to depend on the direction of the electric field. Structural changes, depending on the electric field strength, were completely reversible. Regarding the possible electromechanical coupling phenomena, the piezoelectric and electrostrictive effects have to be considered. Cubic SrTiO3 belongs to the centrosymmetric point group \(m\overline{3}m\) ; hence, no piezoelectric effect is present, whereas second-order effects like electrostriction may occur. Peculiarities arising as a result of the special constraints are discussed.

XAFS study of local structure with picometer accuracy: Th1−xUxO2 and Th1−xPuxO2 solid solutions

XAFS spectroscopy using synchrotron radiation is an extremely suitable technique to study local atomic and electronic structure of mixed Th1−xUxO2 and Th1−xPuxO2 oxides. Despite of XAFS technique overall success, a pico-meter barrier (10-2 Å) exists in XAFS data analysis. Here we present the dependence of the mixed oxide structure on composition, probed by XAFS with picometer accuracy. Complimentary XAFS spectra were measured at the Th, U, and Pu L-edges. We found that opposite to the lattice parameter obtained by XRD, the distances given by XAFS for the first and second shells do not follow completely neither Vegard's law nor the virtual crystal approximation (VCA). The Th–O, U–O and Pu–O distances obtained vary slightly upon dilution. These values are close to the ones expected from Vegard's law but are always smaller than the ones expected in VCA. The U–U(Th) and Th–Th(U) distances vary strongly upon dilution and the values are close to the ones expected from the VCA model but are always smaller than the ones expected by the Vegard law. The average lattice parameter calculated from XAFS data agrees well with a random distribution of metal (Th, U, Pu) and with one calculated from XRD data. With this complementary XAFS data on the local structure around two selected metal ions it is then possible to give a better view on the mixed oxides structure, the distribution of the two metal ions and local distortions in such medium crystal structure studied by XRD.

Luminescence of the PbWO 4 :5% Cd crystal

Emission and excitation spectra, luminescence decay kinetics within 0.5–300 K, and photo-thermally stimulated processes of the exciton and defect-related states disintegration were studied for the PbWO4:5% Cd crystal. The peculiarities observed in the luminescence characteristics are explained under the assumption that a strong Cd-doping results not only in the compensation of an existing lead deficiency but also in the appearance of local CdWO4-type distortions of the PbWO4 crystal lattice structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Surfactant-controlled synthesis of Pd/Ce 0.6Zr 0.4O 2 catalyst for NO reduction by CO with excess oxygen

For the first time, this work reports a surfactant-controlled synthetic method to obtain a nanophase of mesoporous ceria–zirconia solid solution containing cationic defects in the crystalline structure. The incorporation of a cationic surfactant (myristyltrimethylammonium bromide) into the ceria–zirconia solid network not only controlled the pore diameter distribution but also induced creation of the lattice defect. Ceria–zirconia solid solution showed crystal microstrain and structural distortion that varied with the calcination temperature. Compared to pure ceria, the addition of zirconium to the ceria promoted the bulk oxygen reducibility and enhanced the thermal stability of the solid. Hydrogen could be stored into or released from the PdO/Ce 0.6Zr 0.4O 2 catalyst during the TPR procedure, which is associated to the formation/decomposition of a PdH x phase, due to the hydrogen dissociation catalyzed by metallic Pd. At cool start of reaction, NO reduction by CO with excess oxygen over the Pd/Ce 0.6Zr 0.4O 2 catalyst showed selectivity around 100% to N 2. A competition between NO reduction by CO and CO oxidation by O 2 was observed: at reaction temperatures below 200 °C, NO inhibited CO oxidation activity; however, at reaction temperatures above 200 °C, high activity of CO oxidation resulted in an inhibition effect on NO reduction.

Single crystal study on UNi0.5Sb2

Single crystals of UNi1−xSb2 have been grown from an Sb-rich melt and studied by means of X-ray diffraction, magnetic and electrical transport measurements. Crystal structure refinements indicated significant deficiency on the transition metal sites in the tetragonal HfCuSi2-type unit cell, yielding the actual composition UNi0.5Sb2. The single crystals studied order antiferromagnetically below TN=161K and exhibit another phase transition at Tt=60K, presumably caused by a spin-reorientation. No crystal structure distortion could be detected at 10 K. Above TN the electrical resistivity is dominated by a Kondo effect, whereas at lower temperatures it shows a behavior characteristic of antiferromagnets. The overall magnetic and electrical transport properties of UNi0.5Sb2 are highly anisotropic both in the ordered and paramagnetic states.