Rietveld Full-profile Analysis Research Articles

Magnetic phase separation in the (La0.3Sr0.7)0.5Ca0.5FeO3 solid solution with a perovskite structure

The crystal structure and magnetic properties of the (La0.3Sr0.7)0.5Ca0.5FeO3 solid solution with a perovskite structure have been investigated. The solid solution has been synthesized according to the high-pressure technique. The unit cell parameters have been refined using the Rietveld full-profile analysis under the assumption of the single-phase crystalline state and the two-phase model corresponding to the parent compositions. It follows from the calculations that the best agreement between the experimental data and the theoretical curve is observed for the two-phase model. The measurement of the magnetic properties also indicates the coexistence of two magnetic phases.

Phase equilibria and crystal structures of solid solutions in the Sr-Fe-Ni-O system at 1100°C in air

The phase equilibria in the Sr-Fe-Ni-O system at 1100°C in air have been studied by x-ray diffraction, and the corresponding phase diagram at constant temperature and pressure has been constructed. The system has been shown to contain two solid-solution series at 1100°C in air: SrFe1 − x Ni x O3 − δ (0 < x ≤ 0.075, sp. gr. Cmmm) and Sr3(Fe1 − y Ni y )2O7 − δ (0 < y ≤ 0.15, sp. gr. I4/mmm). Neither Sr4(Fe1 − z Ni z )6O13 nor Sr(Fe1 − z Ni z )12O19 solid solutions have been identified. The lattice constants and structural parameters of single-phase samples have been refined by the full profile Rietveld analysis method.

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&lt;sub&gt;0.8&lt;/sub&gt;Co&lt;sub&gt;0.2&lt;/sub&gt;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.

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.

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.

Reversible channel deformation of zeolite omega during template degradation highlighted by in situ time-resolved synchrotron powder diffraction

The thermal dehydration and the degradation of template of zeolite omega, a synthetic analog of mazzite Na 6.6TMA 1.8(H 2O) 22.2[Al 8.4Si 27.6O 72]-MAZ, was studied in situ by synchrotron powder diffraction. The evolution of the structural features was monitored through 25 structure refinements in the temperature range from 30 to 830 °C by full profile Rietveld analysis performed in the P6 3/ mmc space group. Structural refinements allowed the steps of degradation of tetramethylammonium (TMA), the evolution of the occupation of the different water sites and the migration of the Na cations located along the axis of the 12-ring channel towards a new site near the walls of the ring to be monitored. Transient deformations of the framework were highlighted, related to the constrained diffusion of the products of dehydration and degradation through the 8-ring channels. Permanent deformations of the frameworks correspond to the removal of the TMA cations from the gmelinite cages, which induces a relaxation of the strained 180° T1–O2–T1 angles, a widening of the opening of the 8-ring channels and a star-shaped deformation of the 12-ring channels.

Synthesis, structure and oxygen nonstoichiometry of La0.4Sr0.6Co1−Fe O3−

Abstract The samples of La 0.4 Sr 0.6 Co 1− y Fe y O 3− δ ( y = 0.2 and 0.4) were prepared using both conventional ceramic technique and nitrate–citrate precursors technique. The phase identification was made by X-ray diffraction method. The refinement of structural parameters from the XRD and neutron diffraction measurements was performed by full profile Rietveld analysis. Neutron diffraction showed that both samples possess distorted perovskite-type structure. Oxygen nonstoichiometry was measured by chemical analysis and thermogravimetry (TG) analysis in the range 20 ≤ T /°C ≤ 900 and 2E-5 ≤ p O 2 /atm ≤ 4E-1. TG-experiments indicate a relatively fast and reversible oxygen exchange at p O 2 > 1E-2 atm. Mass saturation occurs at T δ increases with increasing temperature and decreasing oxygen partial pressure.

In situ time resolved synchrotron powder diffraction study of thaumasite

Structural changes during dehydration and subsequent decomposition in thaumasite Ca3Si(SO4)(CO3)(OH)6·12 H2O were studied by in situ synchrotron powder diffraction between 303 and 1,098 K. Evolution of the crystal structure was observed through 28 structure refinements, by full profile Rietveld analysis performed in the P63 space group, between 300 and 417 K, whereupon the thaumasite structure was observed to breakdown. Within this temperature range, the cell parameters of thaumasite increased as a function of temperature in a nearly linear fashion up to about 393 K, at which temperature, a slight slope change was observed. Above 400 K, the thermogravimetric analysis revealed that the dehydration process proceeded very rapidly while the refined occupancy of water molecules dropped below a critical level, leading to instability in the thaumasite structure. At a same time, a remarkable change in the unit cell parameters occurring at about 417 K indicated that the crystal structure of thaumasite collapsed on losing the crystallization water and it turned amorphous. This result indicated that the dehydration/decomposition of thaumasite was induced by the departure of the crystallization water. At about 950 K, anhydrite and cristobalite crystallized from the thaumasite glass.

Quasi-one-dimensional oxides Sr4Co3 − x MnxO9 (0 ≤ x ≤ 3): Synthesis and magnetic properties

Sr4Co3 − xMnxO9 (0.5 ≤ x ≤ 2) solid solutions (ss), which belong to the family of quasi-one-dimensional oxides A3n + 3mA′nB3m + nO9m + 6n (where A is an alkaline-earth element, A′ is a 3d element, B is manganese), are prepared using citrate technology. The structures of the phases are described in terms of trigonal space group P321. A full-profile Rietveld analysis shows that the oxides are incommensurate. The structure is described as consisting of two subcells with identical a parameters but different c parameters. Magnetic susceptibility measurements in the range from 2 to 300 K are interpreted on the assumption of the existence of a spin-glass state.

Solid Electrolytes Based on KAlO2-TiO2: The Crystalline Structure and Conduction

The structure of solid high-conductance potassium electrolytes K1 − xAl1 − xTixO2 (x = 0.1; 0.2) at 25 and 575°C is studied by a powder neutron diffraction analysis with the application of full-profile Rietveld analysis. Inserting titanium ions removes in potassium aluminate the phase transition at 540°C and the conductance anisotropy typical for its low-temperature form. Both structures are identical (fcc lattice, space group Fd3m). Experiment and calculation coincide best under the assumption that the potassium sublattice is disordered. The conductance increase upon inserting ions Ti4+ is due, apart from stabilization of the fcc structure, to formation of additional potassium vacancies and larger channels for the migration of potassium cations (ions Ti4+ are larger than ions Al3+).

Temperature-Induced Transformations in CoAPO-34 Molecular Sieve: A Combined In Situ X-ray Diffraction and FTIR Study

Thermally induced processes of CoAPO-34, an aluminophosphate molecular sieve with chabasite-type structure, synthesized in the presence of morpholine as a structure-directing agent and HF as a mineralizing agent, have been studied by in situ X-ray synchrotron powder diffraction augmented with Fourier transform (FT) IR analysis. A time-resolved experiment was performed using a translating imaging plate system. At room temperature, the structure refinement by full-profile Rietveld analysis showed P-1 symmetry and the presence of one Al site with sixfold coordination. At around 400 degrees C, both fluorine and morpholine are lost, and the four-connected chabazite (CHA)-type topology is restored. Notwithstanding the metrically rhombohedral values of the cell parameters, the symmetry remains triclinic P-1. Inhomogeneous dealumination of the framework begins at 725 degrees C, accompanied by a strong triclinization of the unit cell and followed by the collapse of the structure above 775 degrees C. The insertion of cobalt ions within the CHA framework was monitored by FTIR spectroscopy, which showed that bridged Co(2+)-O(H)-P hydroxyls are present after morpholine removal.

Potassium Aluminate Crystalline Structure and Electroconduction

The crystalline structure of low- and high-temperature modifications of KAlO2 is studied by a neutron diffraction method combined with a full-profile Rietveld analysis. At low temperatures KAlO2 has an orthorhombic structure (spatial group Pbca), which turns tetragonal (spatial group P41212) at 540°C. During a phase transition along the c axis there open new conduction channels with a large cross-section of voids, which is a probable reason for the conduction jump. The presumed anisotropy of conduction in the low-temperature modification disappears during the phase transition.

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) → ....

X-ray diffraction analysis of Zn 0.85Co 0.15O powder and thin films

Co-doped ZnO powder and thin films on Si(1 0 0) substrate were prepared by solid-phase reaction and reactive e-beam evaporation. All samples were characterized by X-ray diffraction. The structure of powder sample was determined using Rietveld full-profile analysis method. The study of the influence of substrate temperature on the structure of thin films samples showed that the quality of thin films depended largely on the substrate temperature. The film prepared at 400 °C had the highest quality with c-axis (0 0 2) preferred orientation.

In situ time resolved synchrotron powder diffraction study of mordenite

The step by step thermal dehydration process of the zeolites mordenite from Pashan (Poona, India) (Na 3.51 K 0.14 Ca 1.89 Mg 0.09 Sr 0.01 )[Fe 3+ 0.03 Al 7.40 Si 40.53 O 96 ] · 27.26H 2 O, has been studied in situ by synchrotron powder diffraction. The time-resolved experiment was performed using a translating imaging plate system. The structure refinements by full profile Rietveld analysis were performed in the Cmcm space group in the temperature range from 25 to 830°C. The results of structure refinements indicate that the slight cell-volume contraction (∼ 1.9%) is related to the release of water molecules from the channels: above 375°C, the water loss lead to an enlargement of the 8-membered ring parallel to [010], which occurred by a flattening of T3-O9-T3 and T4-O4-T3 bridges. The dehydration process is reflected not only in the content of water molecules in the zeolite channel, but also in the temperature behaviour of the unit cell parameters. The cell parameters b and c decreased regularly as the temperature rose, whereas a decreased up to 400°C then increased up to 630°C, and finally decreased until the end of experiment. The removal of water molecules was accompanied by a spreading of the initial Ca sites into many positions bonded to the framework oxygens. The increased interaction with the framework oxygens of Ca sites was intimately related to the distortion of the 12-ring which is in turn related to the lengthening of the a cell parameter.

Crystalline Structure and Electroconductivity of Solid Electrolytes Li3.75Ge0.75V0.25O4 and Li3.70Ge0.85W0.15O4

Crystalline structure of low- and high-temperature modifications of solid lithium-conducting electrolytes Li3.75Ge0.75V0.25O4 and Li3.70Ge0.85W0.15O4 are studied by powder neutron diffraction analysis with use made of Rietveld full-profile analysis. The structure of either composition is derivative from γ-Li3PO4. The high conductivity of the electrolytes is connected with the presence of interstitial lithium cations, whose positions are occupied but partially. Phase transitions in the electrolytes consist of the leveling of the occupation degrees of these positions and make practically no impact on the rigid cage of the lattice.

Rietveld analysis of X-ray diffraction pattern from β-Ta2O5 oxide

The structure of low-temperature β-Ta2O5 oxide has been studied by the method of Rietveld full-profile analysis. It is established that this oxide has an orthorhombic structure with lattice parameters a = 6.217 A, b=3.677 A, and c = 7.794 A. The atomic coordinates and thermal parameters are also determined.

Cation-deficient perovskite-related compounds (Ba,La) nTi n–1O 3n (n = 4, 5, and 6): a Rietveld refinement from neutron powder diffraction data

The crystal structures of the three basic members of the homologous series of (Ba,La) nTi n–1O 3n (n = 4, 5, 6) compounds have been re-examined using Rietveld full profile analysis of neutron diffraction patterns. La 4Ti 3O 12 (n = 4) crystallizes with the R 3 space group and the refined unit-cell parameters a = 5.5509(1) Å, c = 26.1780(2) Å, and Z = 3 (R p = 8.48, R wp = 9.08, R bragg = 2.32). The Ba/La ordering in BaLa 4Ti 4O 15 (n = 5) and Ba 2La 4Ti 5O 18 (n = 6) structures has been clarified. These structures can be described as consisting of perovskite-like slabs, n = 4, 5, and 6 corner-sharing TiO 6 octahedra thick, respectively, separated by layers of vacant octahedra. From n = 4 to n = 6, with increasing amount of Ba atoms, the distortion of the mixed AO 3 layers, i.e., the rotation of TiO 6 octahedra around the c axis, decreases. The coordination of the A cation changes from [6 + 3] to [12].

Determination of the crystal structure of CuSnTi by full profile Rietveld analysis

The crystal structure of the new ternary phase CuSnTi is determined by full profile Rietveld analysis of the powder diffractogram. 104 reflections were refined to a final RBragg value of 5.60%. CuSnTi crystallizes with the spacegroup P63/mmc and is isostructural to InNi2. The lattice parameters are a=0.439 555(5) nm and c=0.601 505(9) nm.