Rietveld Profile Refinement Method Research Articles

Structural and Photocatalytic Analysis of Niwo4 Materials

The different pH levels of NiWO4 materials were synthesized by co-precipitation route. The insight unit cell properties were studied by Powder X-ray diffraction (PXRD). The detailed structural analyses were done by Rietveld profile refinement method. The morphology on the surface of the synthesized NiWO4 materials was evaluated by scanning electron microscopic images. The presence of elements in the prepared materials were confirmed by energy dispersive X-ray spectroscopy (EDS) analysis. The photocatalytic activities of prepared materials are performed on methylene blue which is degraded by irradiation of catalyst in 50 minutes under ultra violet light.

Synthesis, structure and optical properties of layered M4Nb6O17⋅nH2O (M = K, Rb, Cs) hexaniobates

Potassium hexaniobate (K4Nb6O17) with 3D-layered and 2D-nanostructured morphological features has been primarily of academic interest due to its catalytic and photophysical properties. Although its microscopic properties are well described in the literature, there remains an absence of support information on the spectroscopic nature arising from the insertion of larger counterions in the crystalline lattice. In the present work, a new protocol for the preparation of layered M4Nb6O17⋅3H2O (M = K, Rb, Cs) hexaniobates is reported, starting from a citric acid aqueous solution comprising the alkali cations and a niobium citrate complex. X-ray powder diffraction, Raman and photoluminescence spectroscopies were employed to examine the implications of alkali metal incorporation. Crystal structures determination was accomplished by Rietveld profile refinement method. The observed occurrence of a pseudo Jahn-Teller effect (PJTE) implies a reduction of NbO6 octahedral symmetry due to the shortening of terminal Nb−OM bond lengths along with O–Nb–O bond angles tilted from 180°. The Raman spectra point to a local structural disorder by increasing the metal radius with characteristic frequencies assigned to variations of Nb–O bond order. Crystal lattice compositions Rb4Nb6O17⋅3H2O and Cs4Nb6O17⋅3H2O materially induce changes in the luminescent properties and strongly distorted octahedral groups yield a brighter PL blue emission at low temperature (77 K).

Thermoluminescence kinetic parameters of Bi4Ge3O12 single crystals

In this work, we present a detailed kinetic study of the thermoluminescence of Bi4Ge3O12 (BGO) single crystals grown by the Czochralski technique. A single crystalline phase was confirmed through X-ray diffraction pattern analysis based on the Rietveld profile refinement method. The thermoluminescent (TL) glow curves were induced by UV or beta radiation and measured between 20°C and 200°C. The glow curves of BGO crystal presented two peaks at 61°C and 90°C for both kinds of radiation. The kinetic parameters, kinetic order (b), activation energy (E) and frequency factor (s), of the TL glow curves have been determined by four different methods. The lifetime of the peaks at room temperature was also determined and used to discuss the stability of the TL peaks at room temperature.

Structure study on the thermoelectric materials Ce xCo 4Sb 12 ( x = 0.5, 1.0) by neutron diffraction

In order to understand the relationship between crystal structure and thermoelectric properties, the neutron diffraction patterns of the thermoelectric materials with the nominal composition Ce x Co 4Sb 12 ( x = 0.5, 1.0) were measured at room temperature, the data were fitted by the Rietveld profile refinement method using the Fullprof2k program. It is found that the sample Ce 0.5Co 4Sb 12 is composed of two phases, its major phase is CoSb 3 with skutterudite-structure and the Ce atom is not incorporated into the lattice, the impurity is monoclinic CoSb 2. In the case of Ce 1.0Co 4Sb 12, the major phase is filled skutterudite, about 10% of the 2a site is occupied by Ce atom, the second phase is monoclinic CoSb 2.

Crystal chemistry of perovskite-type compounds in the tausonite-loparite series, (Sr 1−2 x Na x La x )TiO 3

Perovskite-type compounds in the series tausonite-loparite, (Sr1−2 x Na x La x )TiO3, were synthesized by solid-state reaction (final heating at 1200–1300 °C), and studied using “conventional” and synchrotron X-ray powder diffractometry. The structures of intermediate compositions were determined using the Rietveld profile refinement method. In the compositional range 0 ≤x ≤ 0.1, the series comprises perovskites characterized by an undistorted cubic structure (space group Pm3¯m, a ≈ 3.905–3.902 A, Z = 1). Intermediate compounds in the range 0.15 ≤ x ≤ 0.35 crystallize with tetragonal symmetry (I4/mcm, a ≈ , c ≈ , Z = 4) derived from the cubic aristotype by antiphase rotation of the TiO6 octahedra about a fourfold axis. The angle of rotation estimated from the positional parameters of oxygen atoms ranges from 2.5(7)° to 5.5(4)°. The cubic-to-tetragonal transition arises from substitution of Sr2+ by the comparatively smaller Na1+ and La3+ cations. A further transition from the tetragonal to rhombohedral symmetry (R3¯c, a ≈ , c ≈ 2 , Z = 6) occurs between x = 0.35 and 0.40, and apparently does not involve formation of perovskite with an intermediate two-tilt structure (Imma). The rhombohedral structure is characterized by a multicomponent octahedral tilt about a threefold axis ranging in magnitude from 6.5(2)° to 7.7(2)°. In the series (Sr1−2 x Na x La x )TiO3, the unit-cell dimensions decrease, and the degree of structural distortion increases with x.

Stability of non-stoichiometric lao 1−xf 1+2x phases: x-ray diffraction investigation

Summary The X-ray diffraction patterns of the polycrystalline LaO 1−x F 1+2x (0.05≤x≤0.3) phases were measured at room temperature and analyzed by the Rietveld profile refinement method. All compounds crystallize in the tetragonal PbFCl-type structure with P4/nmm as the space group. No distortion to lower orthorhombic symmetry was observed. The tetragonal lattice parameters a and c increase with increasing excess of fluoride. The La-oxygen (La-fluorine) distances first decrease (increase) but then these trends are reversed. The Global Instability Index calculated from the bond valence model increases towards the higher fluoride content of the compounds indicating decreasing stability

X-ray powder diffraction and vibrational spectroscopic investigation of the LaO(Cl1−xBrx) solid solutions

The formation of the anion solid solutions in the LaO(Cl1−xBrx) (0≤xBr≤1 ΔxBr=0.2) series was studied by the vibrational (FT-Raman) spectroscopic and X-ray powder diffraction (XPD) techniques. The Raman spectra were successfully analyzed by using the factor group analysis. The crystal structures for all members of the system were resolved from the X-ray diffraction data by using the Rietveld profile refinement method. The LaO(Cl1−xBrx) system appears to retain the tetragonal structure throughout the whole series. However, there exists two regions of the tetragonal LaOX (X=C1 or Br) phases: the chloride- and bromide-rich regions between 0≤xBr≤0.4 and 0.4≤xBr≤1, respectively. Only insignificant formation of solid solutions could be observed since the lattice parameter a and c values changed only slightly from those for the pure LaOCl and LaOBr in these two regions. Despite the absence of the solid solubility, no phase separation occurred as predicted by the Vegard's rule since the difference in the ionic radius of the Cl− and Br-ions is only about 8%. The FT-Raman studies yielded practically constant number and energies of the vibrations throughout the whole LaO(Cl1−xBrx) series resulting in similar conclusions.

Characterization of the non-stoichiometry in lanthanum oxyfluoride by FT-IR absorption, Raman scattering, X-ray powder diffraction and thermal analysis

The FT-IR absorption, FT-Raman scattering, X-ray powder diffraction (XPD), and thermogravimetry were used to explore the non-stoichiometry in LaOF. The TGA-DTA analyses between 30 and 1500°C showed that the LaO 1 − x F 1 + 2 x phases yielded the stoichiometric LaOF as an intermediate product. The temperature of formation of the LaOF and La 2O 3 increased with increasing excess of fluoride. The room temperature XPD data in 6.5 ⩽ 2 θ ⩽ 121° range were analyzed by the Rietveld profile refinement method and subsequently by the bond valence calculations. All LaO 1 − x F 1 + 2 x phases possess the tetragonal PbFCl-type structure (space group: P4/ nmm; Z = 2) while the stoichiometric LaOF has the hexagonal SmSI-type structure (space group: R 3m; Z = 6 ). The unit cell parameters a and c as well as the global instability index (GII) values increased with increasing excess fluoride. The GII value for each LaO 1 − x F 1 + 2 x exceeded the limit ( ca 0.2) for a possible breakdown of the tetragonal structure indicating the inherent instability of these phases. The room temperature FTIR and FT-Raman spectra between 100 and 500 cm −1 and 50 and 1000 cm −1, respectively, were investigated using the factor group analysis to get more information of the local structure in LaOF. All four IR modes (2A 2u + 2E u) the for both forms and five of the six Raman modes (3A 1g + 3E g and A 1g + 2B 1g + 3E g) for the hexagonal and the tetragonal form, respectively, were observed. The Raman spectra of the tetragonal LaOCl and all LaO 1 − x F 1 + 2 x were found remarkably similar.

On Some Structural and Spectroscopic Aspects of Rare Earth Oxycompounds

The aim of this account is to present the use and the advantages of different experimental and theoretical methods in the study of the structural and spectroscopic properties of rare earth (RE) oxyfluorides. The structural characterization was carried out with the X-ray and neutron powder diffraction techniques combined with the analysis of the acquired data with the Rietveld profile refinement method. The detailed spectroscopic studies were also used by employing the optical absorption and luminescence as well as inelastic neutron scattering data. Simple spectroscopic measurements gave, however, only qualitative description of the spectroscopic properties studied. More sophisticated and quantitative means was obtained by the application of the phenomenological crystal field theory to the spectroscopic data. On the other hand, the structural data was also used as initial input to electrostatic point charge calculation in order to extract the spectroscopic information. The structural and spectroscopic studies comprised the verification of the exact crystal and energy level structures and the characterization of the different interactions modifying the spectroscopic properties of the RE 3+ ions. Finally, the results from the theoretical model were used to explain the evolution of the crystal field effect on the 4f N energy level structure of the RE3+ ion in the RE oxyfluorides series.

Analysis of the optical spectra and paramagnetic susceptibility of DyOF

The optical absorption spectra of the rhombohedral DyOF were measured at selected temperatures between 9 and 300 K. The emission spectra of the ion in the LaOF and GdOF matrices were obtained at 77 K and room temperature. The energy level scheme of ( electron configuration) was simulated with a Hamiltonian of 20 parameters. The diagonalization of the energy matrices including simultaneously the free ion and crystal field (c.f.) interactions was carried out for the point symmetry of the site. Good correlation with an rms deviation of was obtained between the experimental and calculated energy level schemes of 153 Kramers doublets. The c.f. parameters show only slight distortion from symmetry. A comparison to , , , , and electron configuration) in other REOF matrices showed smooth evolution of the c.f. effect which was discussed in terms of the possible interactions involved. The x-ray powder diffraction pattern of DyOF between was analysed by the Rietveld profile refinement method. The structural data were used to calculate the c.f. parameters by the modified electrostatic point charge model yielding , and values close to the experimental ones, whereas the , , and values were too large. Using the experimental free ion and c.f. wave functions, the paramagnetic susceptibility of DyOF as a function of temperature was simulated. Above the Néel temperature (3.6 K), good agreement was obtained between the calculated and experimental susceptibilities in the paramagnetic range.

Quantitative Determination of Low-Phase Volume Fraction in Ferro-Silicon Alloys by the Rietveld Profile-Refinement Method. Neutron Diffraction Data Compared with Other Methods

Neutron diffraction data collected from ferrosilicon alloy powders have been analysed using the Rietveld profile-refinement method in order to perform a quantitative determination of the phase volume fraction. The results obtained have been compared with those determined from other methods such as imaging analysis, chemical analysis and phase-diagram calculation by a thermodynamic approach. For low phase volume fractions, the Rietveld profile refinement of the neutron-powder-diffractometer data gives results that are more accurate than those from imaging analysis and that are more representative at the ingot scale than those from chemical analysis, owing to the greater quantity of powder analysed. As concerns the thermodynamic calculations, two phase volume fraction determinations may be performed: quantitative, at equilibrium, and qualitative, out of equilibrium.

Solid–solid phase transitions in n-alkanes C23H48 and C25H52: X-ray power diffraction study on new layer stacking in phase V

The solid–solid phase transitions and the crystal structures of odd n-alkanes, n-C23H48, and n-C25H52, were investigated by x-ray powder diffraction. The phase transitions, I→V→RI for n-C23H48 and I→V→IV→RI for n-C25H52, were observed, where phases I, V, IV are the low-temperature ordered phases, and the phase RI is the rotator phase. The crystal structure of phase V was determined by the Rietveld profile refinement method. Phase V is orthorhombic (Pbnm). New molecular layer stacking appears in phase V, while the lamellar structure and the lateral packing of molecules are same as those in phase I and phase IV. The solid–solid phase transitions below the rotator phase transition of odd n-alkanes found to be characterized by the changes in molecular layer stacking are considered to be caused by the increased disorder in the layer surface.

Study of the crystal field effect in REOF:Eu 3+ (RELa, Gd and Y) using optical spectroscopy and X-ray powder diffraction

The luminescence spectra of the Eu 3+-doped rare earth oxyfluorides REOF:Eu 3+ (RELa, Gd and Y) were measured at room and liquid nitrogen temperatures. The interpretation of the spectra and the simulation of the 7F J ( J = 0–5) Stark levels were carried out with the aid of phenomenological crystal field (CF) theory for the C 3v symmetry of the RE 3+ site. The best-fit set of the six non-zero CF parameters yielded the r.m.s. deviations 8, 11 and 10 cm −1 between the experimental and calculated energy levels for YOF, GdOF and LaOF respectively. The strength of the CF effect increases from the LaOF to the YOF host. The X-ray powder diffraction data for LaOF and GdOF were analysed by the Rietveld profile refinement method. From these results the CF parameters were calculated with a modified point charge model. The parameters of ranks four and six were reproduced quite close to the experimental values. The calculated | B 0 2| values were too large, evidently owing to short-range covalency effects.

X-ray powder diffraction and vibrational study of the solid solutions in (La 1− xRE x)OCl (RE=Gd and Y)

The formation of cation solid solutions in the (La 1− x RE x )OCl (RE=Gd and Y) series was studied by vibrational (far-FTIR absorption and FT Raman scattering) spectroscopy and powder X-ray diffraction (XRD). The powder XRD data were further analysed by the Rietveld profile refinement method. The unit cell dimensions evolved linearly between 0⩽ x Gd⩽1 in the (La 1− x Gd x )OCl series. This solid solution retains the tetragonal PbFCl-type structure throughout the whole concentration range. In the (La 1− x Y x )OCl series, additional reflections were observed in the XRD pattern beyond x=0.5. With x=<0.7 this system has also the tetragonal structure but with higher yttrium concentration a separate phase is formed which was tentatively identified as the SmSI-type YOCl. The vibrational spectroscopy studies sustain the results obtained by XRD analysis. All six Raman-active and three of the four IR-active vibrational modes were observed. The energy of these modes evolved linearly in both (La 1− x Ln x )OCl solid solution series. The separate phase was observed for the (La 1− x Y x )OCl system by Raman spectroscopy, too.

High resolution neutron powder diffraction: a case study of the structure of C 60

High resolution time-of-flight neutron powder diffraction has been used to determine the detailed structure of C 60 as a function of temperature. Rapid data collection coupled with high resolution has enabled subtle aspects of the 86 K orientational glass transition and precursor effects of the 260 K order-disorder transition to be observed. This surveying capability complements traditional single crystal methods. The power of the Rietveld method of profile refinement is demonstrated in the elucidation of the detailed crystal structure of the orientationally-ordered low temperature phase and in the evaluation of the departure from isotropic scattering of the C 60 molecule in the disordered high temperature phase. The counter-intuitive success in obtaining high-order cubic-harmonic coefficients, albeit to poorer precision than single crystal X-ray measurements, confirms the efficacy of the Rietveld profile refinement method. The collapse of three dimensions of diffraction information on to the one dimension of a high resolution powder diffraction pattern can still lead to an impressive amount of structural information that substantiates the assertion made by W. H. Bragg ‘the second method [powder diffraction], first used independently by Debye and Hull, can be used when the crystal is in powder, and can, therefore be employed when no single crystal can be obtained of sufficient size. All the spectra of the different planes are thrown together on the same diagram or photograph, and must be disentangled. This is not as difficult as it may seem . . . ’.

Application of ODF to the Rietveld Profile Refinement of Polycrystalline Solid

The Rietveld profile refinement method is probably the most popular technique used for the crystallographic characterization of materials including crystal structures and phase analysis, but it has been used mostly with ideal powder sample, not with textured polycrystals, because effects of strong and complex textures. Most technological materials are fabricated by using thermo-mechanical forming processes, which inevitably produce strong and complex preferential orientations of the crystallites. Consequently, the diffraction patterns of a given technological material are not unique but vary considerably with the measuring direction, with intensity variations as large as factors of hundreds, depending on the degree of texture. The texture effect on the diffraction pattern of a certain sample direction is directly proportional to the pole density of the corresponding inverse pole figure, which can be obtained from the three-dimensional orientation distribution function (ODF) of the material. The ODFs of materials with high crystal symmetry, such as cubic, hexagonal, tetragonal, and orthorhombic, can be determined quite precisely, using modern texture analysis techniques (for example, Bungel, Wenk, and Kallend et al.). The pole density distributions of the inverse pole figures can be used in the diffraction profile calculation of a highly textured sample.

Structure determination of KLaNb2O7 exhibiting ion exchange ability by X-ray powder diffraction

The crystal structure of KLaNb2O7 has been determined from X-ray powder diffraction data. The cell exhibits orthorhombic symmetry and belongs to C222 space-group with a=3.9060(1) Å, b=21.6031(7) Å, c=3.8879(1) Åand Z=2. The structure was refined using a Rietveld profile refinement method. The final reliability factors achieved were RWP=0.0954, RP=0.0676, RI=0.0290 and RF=0.0152. The structure is built up from double perovskite layers, LaNb2O7, interleaved by potassium atoms. The potassium ions were found to be statistically distributed at an interlayer site with an occupation factor of about 0.5. The ion exchange ability of this compound is discussed on the basis of the crystal structure.

Synthesis and crystal structure of lithium phosphorus nitride Li 7PN 4: The first compound containing isolated PN 4-tetrahedra

Single phase Li 7PN 4 was synthesized under nitrogen atmosphere at 620°C by solid state reaction of Li 3N and P 3N 5 with molar ratio 7:1. Li 7PN 4 has cubic symmetry, P 43n, a = 936.48(3) pm, Z = 8 . (Rietveld profile refinement method; X-ray powder diffraction data; R(wp) = 0.099 and R( I, hkl) = 0.0744; 77 nonzero reflections observed, 9 positional parameters refined.) Li 7PN 4 is an ionic solid containing both lithium cations and isolated PN 4 anions. Atomic arrangement in the solid derives from an anti-fluorite type of structure. The PN bond lengths (average: 171 pm) correspond to a bond order of approximately 1 1 4 in the PN 4-tetrahedra. In the cubic unit cell the phosphorus atoms resemble β-tungsten analogous arrangement.

Powder X-ray diffraction studies of a low-temperature phase transition in the n-hexadecane/urea inclusion compound

Powder X-ray diffraction studies of the n-hexadecane/urea inclusion compound have been carried out between 296 and 46 K to investigate structural aspects of the host (urea) structure, particularly in relation to a low-temperature phase transition in this compound. Our results show that, at ca. 150 ± 1 K, the symmetry of the host structure changes from hexagonal (high-temperature phase; space group P6122) to orthorhombic (low-temperature phase; probable space group P212121). This assessment of the transition temperature is in good agreement with previous measurements using other experimental approaches, and our interpretation of the structural change associated with the transition confirms earlier speculations based upon single-crystal X-ray diffraction investigations. Although the transition involves a major change of crystal symmetry, there is only a relatively minor change in the actual distribution of scattering matter within the crystal, and we outline, in general terms, a systematic approach towards rationalizing changes in a powder diffractogram arising from such a transition. No satisfactory determination of the host structure within the low-temperature phase has been reported previously, and since multiple crystal twinning is thought to accompany the phase transition on passing from the high-temperature phase to the low-temperature phase, powder X-ray diffraction represents a more viable route to this information than single-crystal X-ray diffraction. Structure refinement from the powder X-ray diffraction data collected at 120 K has been attempted using the Rietveld profile refinement method.

The magnetic structure of Pd 3MnD 0.53

The magnetic structure of ordered Pd 3MnD 0.53 has been determined using the Rietveld profile refinement method on neutron powder data collected at 4.2 K. The tetragonal crystal structure is described in space group I4/ mmm. A colinear antiferromagnetic structure with a magnetic moment of 4.8 μB/Mn was found. The direction of the magnetic moments forms an angle of 55° with the tetragonal axis.