Orthorhombic Samples Research Articles

Magnetic Tuning of All-Organic Binary Alloys between Two Stable Radicals

Mixtures of 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN)(x)(BImNN)((1-x)) with x < 0.8 gives orthorhombic unit cells, while x ≥ 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4-300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12-22 K). Interchain exchange is estimated to be 33- to 150-fold weaker, based on antiferromagnetic ordered phase formation below Néel temperatures in the 0.4-1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 - x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.

Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics

Abstract BaTiO 3 ceramics were prepared by conventional sintering technique with a special emphasis on the effects of sintering temperature (1100–1230 °C) on the crystalline structure and piezoelectric properties. XRD patterns indicated that the crystallographic structure changed from tetragonal phase to orthorhombic one with raising sintering temperature from 1160 °C to 1180 °C. Domains were shaped in a stripe and a herringbone in orthorhombic samples for BaTiO 3 ceramics. The domain width and domain density increased with raising sintering temperature. The BaTiO 3 ceramic sintered at 1190 °C showed the excellent electrical properties, d 33 = 355 pC/N, k p = 40%, P r = 10.2 μC/cm 2 , respectively, which are originated to the contributions of both the crystallographic structure transition and nano-domain.

Neutron Powder Diffraction Study of the Effect of Mn-Doping on SrTiO&lt;sub&gt;3&lt;/sub&gt;

The effect of manganese doping on the magnetic and structural properties of strontiumtitanate (SrTiO3) was studied. Neutron powder diffraction, x-ray diffraction, magneticmeasurements, scanning electron microscopy and energy dispersive spectroscopy of x-rays wereutilized. Air-sintered Sr(MnxTi1-x)O3 (SMT) with x = 0:02 and x = 0:05 were homogeneoussingle phase orthorhombic (space group Pbnm) perovskite samples. The symmetry was orthorhombicalready at room temperature, and no symmetry change was observed down to 11K. An anomaly in the magnetic susceptibility was observed in x = 0:02 sample at 75 K. Incontrast to earlier reports, no ferromagnetism was observed.

Thermal stabilities of hexagonal and orthorhombic YbFeO3 synthesized by solvothermal method and their catalytic activities for methane combustion

Thermal stabilities of hexagonal and orthorhombic YbFeO3 samples synthesized by the solvothermal method were investigated. The morphology and BET surface area of hexagonal YbFeO3 did not change by calcination, while orthorhombic YbFeO3 easily sintered, resulting in a decrease of the BET surface area. The hexagonal YbFeO3 sample, which had a high surface area (29 m2/g) after calcination at 800 °C, had higher catalytic activity for methane combustion than the orthorhombic YbFeO3 samples calcined at 800 °C.

Dielectric and Thermal Investigations on PbNb2O6 in Pure Piezoelectric Phase and Pure Non-Piezoelectric Phase

A high piezoelectric transition temperature is indicated for present orthorhombic samples of lead meta-niobate (PbNb2O6) by the high value of the temperature (Tm) at which the real part (ϵ′) of electrical permittivity peaks. It is 573 to 580°C. The imaginary component (ϵ″) increases sharply at these temperatures. Cooling run after heating to 700°C gives changed values of ϵ′ and ϵ″ and Tm. Present work reports impedance spectroscopy (up to 700°C over 20 Hz to 5.5 MHz) and Differential Scanning Calorimetry or DSC on the pure orthorhombic phase, and, for the first time, on the pure rhombohedral phase. DSC shows an endothermic dip across Tm during heating and an exothermic peak during cooling for the orthorhombic sample only.

Structural Characterization of Orthorhombic and Rhombohedral Lead Meta-Niobate Samples

The meta-stable orthorhombic phase of lead meta-niobate (PbNb2O6), as obtained by quenching, is piezoelectric, but difficult to prepare in pure state as a few competing phases like the non-piezoelectric rhombohedral PbNb2O6 tend to form during the preparation. However, it can have an attractively high Curie temperature above 570°C. High Curie temperature piezoelectric sensors are desirable for imaging and other applications in certain industrial and research sectors. Presently, both phases have been synthesized as single phase samples as shown here from structural Rietveld analysis of their XRD. Characterization of both compounds by FTIR and XRD have been carried out and presented.

Influence of structure on infrared emissivity of lanthanum manganites

The lanthanum manganites La 1− x Sr x MnO 3 (0.1≤ x≤0.3) were prepared by standard solid-state reaction and sol–gel method, respectively. The structure, magnetization curves, infrared absorption and infrared normal emissivity ( ε N ) in the 3–5 and 8–14 μm wavebands of the samples were systematically investigated. The samples prepared by solid-state reaction are rhombohedral, and the samples obtained by sol–gel method are orthorhombic with irregularities in size and shape. The slight shoulder appearing on the peak of orthorhombic sample may be due to the asymmetric vibration in distorted lattice, and no infrared absorption occurs in the 3–5 and 8–14 μm wavebands. The ε N of both samples decreases with increasing doping level, and due to stronger metallic character suggested by magnetization results, rhombohedral samples exhibit lower ε N values than orthorhombic ones. The ε N values in the 8–14 μm waveband are higher than those in the 3–5 μm waveband, and the ε N of rhombohedral sample changes significantly in the temperature range 293–328 K. For orthorhombic sample, the ε N increases slightly in the whole temperature range due to the weakening of the double-exchange interaction between Mn 3+ and Mn 4+.

Analysis of cubic and orthorhombic C3A hydration in presence of gypsum and lime.

Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) have been used to study the microstructural changes and phase development that take place during the hydration of cubic (pure) and orthorhombic (Na-doped) tricalcium aluminate (C3A) and gypsum in the absence and presence of lime. The results demonstrate that important differences occur in the hydration of each C3A polymorph and gypsum when no lime is added; orthorhombic C3A reacts faster with gypsum than the cubic phase, forming longer ettringite needles; however, the presence of lime slows down the formation of ettringite in the orthorhombic sample. Additional rheometric tests showed the possible effects on the setting time in these cementitious mixes.

Calorimetric Studies on the Phenolic Glycoside D(–)-Salicin

A pure orthorhombic phase sample of D(–)-salicin was purified and characterized for calorimetric measurements. From differential scanning calorimetry (DSC) measurements it was found that the onset and maximum temperatures of the fusion peak were Ton = (473.30 ± 0.05) K and Tmax = (474.74 ± 0.05) K, respectively, and that the corresponding standard enthalpy of fusion was ΔcrlHm° = (55.5 ± 0.4) kJ mol−1. From the last two values the standard entropy of fusion is calculated as ΔcrlSm° = (116.9 ± 0.4) J mol−1 K−1. The standard molar enthalpy of formation of orthorhombic D(–)-salicin at T = 298.15 K, was determined as ΔfHm°(C13H18O7, cr, orthorhombic) = −(1366.9 ± 3.2) kJ mol−1, by combustion calorimetry. From the results of solution calorimetry obtained in this work and some auxiliary values taken from the literature the enthalpy of reaction of hydrolysis of D(–)-salicin to produce β-glucose and o-hydroxybenzyl alcohol was found marginally thermoneutral, if the uncertainty interval was considered. Additionally, specific heat capacity measurements on the orthorhombic phase, glass and liquid-quenched glass obtained by DSC was reported. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5354–5362, 2008

Elastic anomalies accompanying phase transitions in (Ca,Sr)TiO3 perovskites: Part III. Experimental investigation of polycrystalline samples

Bulk and shear moduli of polycrystalline samples of perovskites with different compositions across the CaTiO3-SrTiO3 solid solution have been measured at ambient conditions and in-situ at high pressures by pulse-echo ultrasonic methods. The samples were prepared as dense pellets by hot pressing synthetic powders at {approx}7.5 GPa and {approx}1000 C. Any variations of bulk modulus due to phase transitions are small, but significant anomalies have been observed in the shear modulus at ambient conditions. These are associated with a sequence of symmetry changes PmFormulam -> I4/mcm -> Pbcm -> Pnma with increasing CaTiO3 content. Comparison with variations in elastic properties predicted using Landau theory suggests that a substantial part of the elastic softening observed in tetragonal samples could be due to anelastic contributions from transformation twin walls. This additional softening does not occur in orthorhombic samples, and the transition from tetragonal to orthorhombic symmetry results in a stiffening of the shear modulus. No overt evidence was found for a phase transition I4/mcm {leftrightarrow} Pnma at high pressures in Ca0.35Sr0.65TiO3 but small changes in the trends of both bulk and shear moduli in the range 2.5-3 GPa could be due either to a different transition or a change in compression mechanism.more » A PmFormulam {leftrightarrow} I4/mcm transition at {approx}2 GPa in Ca0.05Sr0.95TiO3 shows the same form of softening as observed for the transition as a function of composition. A simple model of twin wall contributions to the compliance of tetragonal samples failed to match the observed variations that, alternatively, seem to follow {Delta}G {proportional_to} q4 where {Delta}G is the change in shear modulus and q4 the driving order parameter for the PmFormulam {leftrightarrow} I4/mcm transition. Analogous elastic behavior is expected to occur in (Mg,Fe)SiO3 and CaSiO3 perovskites at high pressures and temperatures.« less

Raman Active Phonons in RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu,Gd, and Dy) Perovskites

We examine RCoO3 (R=La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy)perovskites prepared with the solid-state reaction method by Ramanspectroscopy, and report the Raman active phonons in the RCoO3perovskites crystallized in cubic symmetry for RCoO3 (R=La,Ce, Pr and Nd) and orthorhombic symmetry for RCoO3 (R=Sm, Eu,Gd, and Dy). It is found that the Raman spectra of RCoO3perovskites are strongly dependent on the ionic radius of the rareearth elements, and the frequency shift of the most intense modes ofthe orthorhombic samples are correlated with some structural parameterssuch as Co–O bond distances, ionic radius of the rare earth elementsand Jahn–Teller distortion. It is clear that Raman spectroscopy hasthe advantage of sensitivity to structure distortion andoxygen motion.

Effect of oxygen deficit on magnetic properties of LaCo 0.5Fe 0.5O 3

LaCo 0.5Fe 0.5O 3+d system has been prepared using different thermal treatments by conventional ceramic technology. The samples prepared at 1570 K in air and below this temperature are mixtures of orthorhombic and rhombohedral phases. Increasing temperature up to 1670 K stabilizes the rhombohedral phase whereas annealing in vacuumed quartz tube with a metallic getter results in orthorhombic single-phase structure. All the samples exhibit the ferromagnetic component at temperatures up to 360 K as a result of Dzialoshinsky–Moriya interactions between the Fe 3+ ions. The orthorhombic samples have a giant magnetic anisotropy, mostly associated with Co 2+ ions. Co 3+ ions are supposed to adopt a low spin state.

AC susceptibility and specific heat of UAuAl

We present the AC susceptibility, DC magnetization and specific heat measurements on an orthorhombic polycrystalline UAuAl sample. The results show typical cluster glass behaviors at low temperatures. To characterize the spin freezing state of this system, the static spin freezing temperature T s , critical exponent z ν and activation energy E a are determined from the dynamical analyses of the AC susceptibility data.

Local Structure and Electronic Properties of the Rhombohedral and Orthorhombic Colossally Magnetoresistive Manganites La1-xNaxMnO3 by Mn−K Edge EXAFS and XANES

The local structure and electronic properties of Mn in Na doped lanthanum manganites have been investigated by means of Mn-K edge XAFS, at various temperatures ranging from RT to 30 K. The hole content depends on the amount of doping, both with Na which injects two holes per doping atom and with oxygen nonstoichiometry. The holes are annihilated by oxygen under-stoichiometry via the formation of oxygen vacancies; the presence of a greater static disorder in the orthorhombic manganites is evidenced by both EXAFS and XANES analysis. In the rombohedral samples, a single Mn-O distance is found. In addition, the trend of the EXAFS Debye-Waller factors for the Mn-O distance can be fitted with a simple Einstein model, with no static disorder at low temperature. This evidence suggests small disorder of polaronic and of Jahn-Teller origin in the rombohedral samples at low temperatures, which is in contrast with what was found for the orthorhombic samples below T(c).

Attenuation of ultrasonic waves in rolled metals

Scattering of ultrasonic waves in polycrystals with texture is studied in this article. The attenuations of the three wave modes are determined as a function of dimensionless frequency and propagation direction, respectively, for given orientation distribution coefficients (ODCs). The calculation is done in the case of a statistically orthorhombic sample made up of cubic crystallites. The wave propagation and scattering model is formulated by the Dyson equation using an anisotropic Green's function approach. Within the limits of the first-order smoothing approximation, the Dyson equation is solved in the spatial Fourier transform domain. The results presented are shown to be directional dependent, frequency dependent, and especially dependent on the texture coefficients (ODCs) for the quasilongitudinal and two quasishear waves. The theoretical results presented may be used to improve the understanding of the microstructure during recrystallization processes.

A comparison between thermal expansion properties of hydrated and dehydrated orthorhombic HZSM-5 zeolite

Three different samples of orthorhombic HZSM-5 were analyzed by high-temperature X-ray diffraction and differential scanning calorimetry in order to elucidate the differences in thermal expansion behavior between its hydrated and dehydrated form. The first sample was the as-received orthorhombic HZSM-5, containing three different water species (H 2O, H 3O + and OH). The second sample was previously heat treated in a tubular furnace at 550 °C, and, contained only H 2O, reabsorbed on cooling. The third one was prepared to be completely dehydrated. The dehydrated orthorhombic HZSM-5 sample showed positive thermal expansion from room temperature to 300 °C and negative thermal expansion from 300 °C to 800 °C. On the other hand, the hydrated orthorhombic HZSM-5 exhibited, for the temperature range where water species are present, negative thermal expansion from room temperature to 300 °C (for lattice parameters a and c and volume) and positive thermal expansion from 300 °C to 500 °C. The mechanisms that could explain the thermal expansion behavior of HZSM-5 were discussed.

Selective self-propagating combustion synthesis of hexagonal and orthorhombic nanocrystalline yttrium iron oxide

Macroporous nanocrystalline YFeO3 was prepared by a self-propagating combustion method using yttrium nitrate and iron nitrate as precursors and glycine as a fuel. The phase structure of the product can be selectively controlled to be hexagonal or orthorhombic by simply adjusting the ratio of glycine to nitrate. The samples were characterized by X-ray diffraction (XRD) analysis, N2 adsorption, micro-Raman spectroscopy, Fourier transform infrared absorption spectroscopy (FT-IR), thermal analysis (TGA/DSC), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and magnetic property analysis. Photocatalytic activity for the degradation of methylene blue in water under visible light irradiation shows that the orthorhombic YFeO3 is superior to the hexagonal form. More adsorbed oxygen and ferromagnetism of the orthorhombic sample may explain its high activity.

Determination of volume fractions of texture components with standard distributions in Euler space

The intensities of texture components are modeled by Gaussian distribution functions in Euler space. The multiplicities depend on the relation between the texture component and the crystal and sample symmetry elements. Higher multiplicities are associated with higher maximum values in the orientation distribution function (ODF). The ODF generated by Gaussian function shows that the S component has a multiplicity of 1, the brass and copper components, 2, and the Goss and cube components, 4 in the cubic crystal and orthorhombic sample symmetry. Typical texture components were modeled using standard distributions in Euler space to calculate a discrete ODF, and their volume fractions were collected and verified against the volume used to generate the ODF. The volume fraction of a texture component that has a standard spherical distribution can be collected using the misorientation approach. The misorientation approach means integrating the volume-weighted intensity that is located within a specified cut-off misorientation angle from the ideal orientation. The volume fraction of a sharply peaked texture component can be collected exactly with a small cut-off value, but textures with broad distributions (large full-width at half-maximum (FWHM) need a larger cut-off value. Larger cut-off values require Euler space to be partitioned between texture components in order to avoid overlapping regions. The misorientation approach can be used for texture’s volume in Euler space in a general manner. Fiber texture is also modeled with Gaussian distribution, and it is produced by rotation of a crystal located at g 0, around a sample axis. The volume of fiber texture in wire drawing or extrusion also can be calculated easily in the unit triangle with the angle distance approach.

New insight into the crystal structure of orthorhombic edingtonite: evidence for a split Ba site

AbstractOrthorhombic edingtonite has been found coexisting with tetragonal edingtonite in a specimen from Ice River, British Columbia, Canada.We report data on the composition and crystal structure of the orthorhombic sample. Lattice parameters are:a= 9.5341(6),b= 9.6446(6),c= 6.5108(7)Å, V = 598.68(8)Å3. The crystal structure was refined in space groupP21212 toR1= 1.8% using 879 observed reflections. For the first time, evidence for splitting of the extra-framework Ba site in two different sites (Ba1, Ba2), ~0.37 Å apart, is demonstrated. A comparison with the published crystal structures of tetragonal and orthorhombic edingtonite is made.The present result supports the suggestion that the two edingtonite phases are a consequence of different nucleation phenomena and not different physicochemical conditions.

Ｘ線ＣＴによる不均質材料中の亀裂開口量評価

An improved crack projection method for the analysis of open crack was introduced by applying image subtraction technique. In order to evaluate crack opening in the heterogeneous materials such as rocks, X-ray CT image subtraction method was introduced in the data processing together with necessary noise reduction method, using the 3-dimensional data given by X-ray CT. This is a promising method to analyze open cracks in the heterogeneous materials from the difference of X-ray CT images. The characteristic point of the method is that the reduction and the elimination of fatal noise related to X-ray CT images are possible and that the accurate image processing is expected. The fundamental formulae of noise reduction technique were firstly described and applicability for the rock sample was discussed. Then, formulae for X-ray CT image subtraction method were introduced as well as the necessary data processing for the crack opening measurement. In this study, artificial cracks were simulated by a couple of semilunar shaped rock samples. In order to verify the applicability of the method to the hetelogeneous materials, the rock samples were made of granite. The subtraction method was applied to the rock samples and the accuracy of the method was discussed. It was found that the influence of noises was clearly eliminated and that the crack opening distribution was accurately evaluated. This technique was also applied to the orthorhombic rock sample and it was also proved that crack opening could be evaluated by the same procedure in the case that tomography and data processing were conducted in the same condition.