Full-profile Analysis Research Articles

Mechanism of thermal decomposition of the nonstoichiometric compound YBa2Cu3O6.8

Thermal decomposition of the nonstoichiometric high-temperature superconductor YBa2Cu3O6.8 at a temperature of 200°C in air has been investigated using the full-profile analysis of X-ray diffraction lines. Two mechanisms of decomposition are revealed. The first mechanism, i.e., separation into two phases with a different oxygen content, occurs continuously. The second mechanism, i.e., disordering of the heavy atoms Y, Ba, Ba, Y along the crystallographic axis c, begins to occur after a 20- to 35-h annealing and progresses with a further annealing.

Synthesis, structure, and properties of solid solutions based on bismuth ferrite

Solid solutions of Bi1 − x Pb x Fe1 − x Zr x O3 (x = 0.1−0.2) are synthesized by the methods of liquid-phase and modified solid-phase synthesis. Also, solid solutions of [Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3, and [Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3 (Ln - La, Pr, Gd, Yb) are made, including synthesis of their precursors with organic ligands. Comprehensive investigations involving thermal analysis, IR spectroscopy, X-ray powder diffraction, atomic force microscopy, dielectric and magnetic measurements, and neutron powder diffraction are performed. The full-profile analysis of X-ray and neutron diffraction patterns by the Rietveld method shows that, over the whole temperature interval of 10–700 K under study, the Bi0.9Pb0.1Fe0.9Zr0.1O3 and Bi0.8Pb0.2Fe0.8Zr0.2O3 compounds are characterized by the perovskite structure (space group R3c). The magnetic measurements reveal an antiferromagnetic phase transition in the Bi0.9Pb0.1Fe0.9Zr0.1O3 and Bi0.8Pb0.2Fe0.8Zr0.2O3 solid solutions. The Neel temperature (T N ) decreases considerably with growing PbZrO3 concentration as compared to the Neel point in pure BiFeO3 (T N = 633 K). The perovskite structure with a hexagonal distortion is found in lanthanide-substituted solid solutions and specific features of the surface morphology of the ceramics are analyzed. The magnetic measurements suggest the presence of an antiferromagnetic phase transition in the solid solutions under study, with a considerable drop of T N in the Ln-alloyed compound as compared to the T N value in pure BiFeO3

Topside measurements at Jicamarca during solar minimum

Abstract. Long-pulse topside radar data acquired at Jicamarca and processed using full-profile analysis are compared to data processed using more conventional, range-gated approaches and with analytic and computational models. The salient features of the topside observations include a dramatic increase in the Te/Ti temperature ratio above the F peak at dawn and a local minimum in the topside plasma temperature in the afternoon. The hydrogen ion fraction was found to exhibit hyperbolic tangent-shaped profiles that become shallow (gradually changing) above the O+-H+ transition height during the day. The profile shapes are generally consistent with diffusive equilibrium, although shallowing to the point of changes in inflection can only be accounted for by taking the effects of E×B drifts and meridional winds into account. The SAMI2 model demonstrates this as well as the substantial effect that drifts and winds can have on topside temperatures. Significant quiet-time variability in the topside composition and temperatures may be due to variability in the mechanical forcing. Correlations between topside measurements and magnetometer data at Jicamarca support this hypothesis.

Hybrid genetic algorithm for a full-profile analysis of XRD powder patterns

Hybrid genetic algorithm for a full-profile analysis of XRD powder patterns

Synthesis and structure analysis of aluminum doped zinc oxide powders

Hexagonal Al-doped zinc oxide (ZnO) powders with a nominal composition of Zn1−xAlxO (0⩽x⩽0.028) were synthesized by the co-precipitation method. The contents of the Al element in the samples were measured by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The structures of the Zn1−xAlxO (0⩽x⩽0.028) compounds calcined at 1000 and 1200°C have been determined using the Rietveld full-profile analysis method. Rietveld refinements of the diffraction data indicated that the addition of Al initially has a considerably positive effect on the decreasing of the lattice parameters a and c of Zn1−xAlxO, but the effect becomes very slight and even negative with the further increase of the Al content. The solid solubility limit of Al in ZnO (mole fraction y) is 2.2l%, resulting in Zn0.978Al0.22O. It seems that when the Al content is excessive, Al prefers to form a ZnAl2O4 compound with ZnO, but not to incorporate into the ZnO lattice to occupy the Zn2+ cites. Two phases, [ZnO] (or Al-doped ZnO) and [ZnAl2O4], are obviously segregated in Zn1−xAlxO while the value of x is larger than 0.024. The UV-Vis absorption spectra show that the Al-doped ZnO exhibits a red-shift in the absorption edge without reduced transmission compared with pure ZnO, which also confirms that Al ions enter the ZnO lattice and form a Zn1−xAlxO solid solution.

Structural and Optical Properties of Zn<sub>0.8</sub>Co<sub>0.2</sub>O Ceramics

The Zn0.8Co0.2O ceramics were synthesized by the solid state reaction method with the mixture of ZnO and CoO powders. The mixed powders were sintered at 1200 °C and 1300 °C for 4 hours. It was found that the X-ray diffraction patterns of Zn0.8Co0.2O ceramics were similar to that of the pure ZnO one. The crystal structure of Zn0.8Co0.2O ceramics were then determined using the Rietveld full-profile analysis method to indicate a single phase with a wurtzite-like structure. Their microstructures were examined using the scanning electron microscopy. The results showed that their grain sizes were increased with increasing both the sintering temperatures and the doping effect. Moreover, the optical absorption spectra using UV-Vis spectrometer showed that there were several extra absorption bands appearing in the Zn0.8Co0.2O samples. This confirms that Co2+ is substituted Zn2+ in the wurtzite structure.

Full profile incoherent scatter analysis at Jicamarca

Abstract. Incoherent scatter data from a hybrid long-pulse/double-pulse experiment at Jicamarca are analyzed using a full-profile analysis similar to the one implemented by Holt et al. (1992). In this case, plasma density, electron and ion temperatures, and light ion composition profiles in the topside are estimated simultaneously. Full-profile analysis is crucial at Jicamarca, since the long correlation time of the incoherent scatter signal at 50 MHz invalidates conventional gated analysis. Results for a 24 h interval in April of 2006 are presented, covering altitudes through 1600 km with 10 min time resolution, and compared with results from the NRL ionospheric model SAMI2. The analysis provides the first comprehensive assessment of ionospheric conditions over Jicamarca at sunrise as well as the first 24-h record of helium ion layers. Possible refinements to the experiment and the algorithm are discussed.

Crystal-structure refinement of τ3-Cr4(Al, Si)11 by full-profile Rietveld analysis

Crystal structure of the triclinic ternary phase Cr4(Al, Si)11 was investigated by full-profile Rietveld analysis of powder diffraction data. Four hundred eighty-four reflections were refined to a final RBragg value of 5.00%. Cr4(Al, Si)11 is isostructural to Mn4Al11. Silicon atoms enter into the structure by partially replacing aluminium on the Al(1) and Al(2) sites.

Structure of the mixed oxides Me x (Ce0.5Zr0.5)1−x O y (Me = Gd, Pr)

The structure of the mixed oxides Me x (Ce0.5Zr0.5)1−x O y (x = 0, 0.1–0.30; y < 2) doped with trivalent Gd and Pr metals is investigated using the X-ray powder diffraction analysis, the full-profile analysis of the diffraction pattern, and EXAFS spectroscopy. The mixed oxides are solid solutions with a structure similar to the CeO2 structure. An increase in the content of the introduced trivalent metal brings about an increase in the unit cell parameter and a disordering of the structure of the oxides under investigation.

Synthesis, structure, and conduction of solid solutions BIMEVOX (Me = Cu, Ti)

Conditions for synthesizing single-phase solid solutions Bi4V2 − x Cu x/2Ti x/2O11 − x and Bi4 − x/2V2 − x/2Cu x/2Ti x/2O11 − x/2 are studied. The sequence of phase transformations is determined. Possible domains of stability of polymorphic modifications and the overall conductivity as a function of temperature and composition are studied. The structure of the γ-modification is refined using Rietveld’s full-profile analysis.

Structural study of highly dispersed cerium dioxides

Cerium dioxide samples of different dispersivity, obtained by different methods, have been investigated by X-ray diffraction (XRD) analysis, full-profile analysis of diffraction patterns, calculation of radial distribution function (RDF) of electron density, and extended X-ray absorption fine-structure (EXAFS) spectroscopy. According to the XRD data, the samples studied can be identified in the fluorite structure with conventional unit-cell parameters. However, the local structure of highly dispersed samples, determined by the RDF and EXAFS methods, changes: the coordination spheres for the Ce-O distances are represented by two distances.

The influence of reactants and Al/Ga/Si ratios on the synthesis of CGS structured zeolites

ECR-9 (CGS) zeolites have been synthesised from gallosilicate and gallo-aluminosilicate gels at between 100 °C and 220 °C using several Al and Si reactant types. Aluminum was substituted for gallium in the framework at levels up to 20% in seeded syntheses, but higher Al substitutions promote the crystallization of impurities. This is the first report of a gallo-aluminosilicate CGS composition. We successfully used the Simulated Framework Annealing method to solve the structural topology as if ECR-9 was a novel gallosilicate. The structure was refined using Rietveld full profile analysis (wRp = 14.6%) of powder synchrotron X-ray diffraction data.

X-ray Structural Modeling and Gas Adsorption Analysis of Cagelike SBA-16 Silica Mesophases Prepared in a F127/Butanol/H2O System

A detailed characterization of large-pore cagelike mesoporous SBA-16 silica materials with tailored pore dimensions is reported. The materials were synthesized in a EO106PO70EO106 (F127)−butanol−H2O system under mildly acidic conditions, and the pore diameters were tailored by varying the hydrothermal treatment temperature. Structural information was acquired by full-profile analysis of powder X-ray diffraction (XRD) patterns. High-resolution diffraction data were obtained for all the materials using synchrotron radiation as the X-ray source, enabling a comprehensive XRD modeling supplemented with the generation of electron density distribution maps. The structural parameters derived from the XRD modeling were compared with data obtained from nitrogen and argon physisorption experiments performed at −196 °C. An excellent agreement was found between the XRD modeling results and those obtained by a new nonlocal density functional theory (NLDFT) kernel developed for pore size analysis based on gas adsorption...

Test of applicability of some powder diffraction tools to nanocrystals

The paper is focused on showing systematic difficulties involved in structure analysis of nanocrystals using diffraction, caused by two factors characteristic for nanocrys- tals: disobeying of the Bragg law and dependence of lattice constant from the crystallite size. Although the effect on estimations via Scherrer equation may be considered negligible the Warren-Averbach analysis can be seriously affected as well as the results of a full profile analysis.

Cation distribution and interatomic interactions in oxides with heterovalent isomorphism: X. Structure of the Ho2SrAl2O7 oxide at 100, 298, and 673 K

Crystallochemical data for the Ho2SrAl2O7 oxide at 100, 293, and 673 K were obtained by full-profile X-ray analysis. Analysis of the thermal expansion anisotropy showed that increased temperature gives rise to equalization of metal-oxygen bond lengths in all oxygen polyhedra at the expense of lengthening of some bonds and virtual invariability of others.

High-resolution strain mapping in bulk samples using full-profile analysis of energy dispersive synchrotron X-ray diffraction data

The feasibility of high-resolution strain mapping in bulk samples with both high-spatial and strain resolution is demonstrated using high-energy X-rays between 100 and 300keV on beam line ID15A at the ESRF. This was achieved by using a multiple-peak Pawley-type refinement on the recorded spectra. An asymmetric peak profile was necessary in order to obtain a point-to-point strain uncertainty of 10−5. The presented results have been validated with alternative methods, in this case FE model predictions. This technique promises to be a significant development in the in situ characterisation of strain fields around cracks in bulk engineering samples. The implication of slit size and grain size are discussed. This paper is a concise version of the work published in [A. Steuwer, J.R. Santisteban, M. Turski, P.J. Withers, T. Buslaps, J. Appl. Cryst. 37 (2004) 883].

Study of lipid profile from RIQAS quality control sample

The laboratory of the present author is a participant of Randox International Quality Assessment Scheme (RIQAS). The author receives twenty six samples for thirty nine general chemistry analysis per year, reports of which are to be sent fortnightly. Amongst thirty nine analytes there are partial lipid profile parameters like total cholesterol and triglycerides. So, the author decided to run a pilot study of full lipid profile from these samples. At the first phase four samples from two different cycles were considered as test materials. The reports of these samples were quite satisfactory. The trial run was given for fifteen consecutive days. (Presented by the author in the Annual Conference of ACBI, 2004).The success of trial runs for fifteen days proved that EQA samples from RIQAS may be used for full lipid profile analysis. Results were compared against Randox internal quality control samples (IQA) and were found to be accurate and reproducible.

Thermolysis of [Pt(NH3)4][ReHlg6] (Hlg = Cl, Br). Structure refinement for [Pt(NH3)4][ReCl6

Thermal decomposition of [Pt(NH3)4][ReHlg6] binary complex salts (Hlg = Cl, Br) in a hydrogen atmosphere has been studied. Polycrystal X-ray diffractometry indicated that two-phase metallic systems are the final products of thermolysis. Structure refinement was performed for [Pt(NH3)4][ReCl6] by the combined technique involving decomposition of the diffractogram into individual reflections, isolation of reflections most sensitive to the position of separate light atoms, and full-profile analysis. Crystal data for PtReN4Cl6H12: a = 11.616(1) A, b = 10.998(1) A, c = 10.377(1) A, V = 1148.1 A3, space group Cmca, Z = 4, dx = 3.831 g/cm3. The indices are Rp = 5.48%, Rwp = 10.01%, R(F2) = 12.62%. The coordination polyhedron of Re is an almost regular octahedron: Re-Cl 2.34–2.36 A, ∠ Cl-Re-Cl 86.9–90.3°; the coordination polyhedron of Pt is a square: Pt-N 2.04 A, ∠N-Pt-N 90.4°.

High-resolution strain mapping in bulk samples using full-profile analysis of energy-dispersive synchrotron X-ray diffraction data

The feasibility of both high spatial and strain resolution is demonstrated using high-energy X-rays between 100 and 300 keV on beamline ID15A at the ESRF. The data analysis was performed using a multiple-peak Pawley-type refinement on the recorded spectra. An asymmetric peak profile was necessary in order to obtain a point-to-point uncertainty of 10−5. The measurements have been validated with complementary techniques or reference data.

Structure, ionic conduction, and phase transformations in lithium titanate Li4Ti5O12

The spinel structure of lithium titanate Li4Ti5O12 is refined by the Rietveld full-profile analysis with the use of x-ray and neutron powder diffraction data. The distribution and coordinates of atoms are determined. The Li4Ti5O12 compound is studied at high temperatures by differential scanning calorimetry and Raman spectroscopy. The electrical conductivity is measured in the high-temperature range. It is shown that the Li4Ti5O12 compound with a spinel structure undergoes two successive order-disorder phase transitions due to different distributions of lithium atoms and cation vacancies (□, V) in a defect structure of the NaCl type: (Li)8a[Li0.33Ti1.67]16dO4 → [Li□]16c[Li1.33Ti1.67]16dO4 → [Li1.33□0.67]16c[Ti1.67□0.33]16dO4. The low-temperature diffusion of lithium predominantly occurs either through the mechanism ... → Li(8a) → V(16c) → V(8a) → ... in the spinel phase or through the mechanism ... → Li(16c) → V(8a) → V(16c) → ... in an intermediate phase. In the high-temperature phase, the lithium cations also migrate over 48f vacancies: ... Li(16c) → V(8a, 48f) → V(16c) → ....