Rietveld refinement

In this study, sol-gel method using egg white as emulsifying agent was applied to prepare nano size spinel NixFe3-xO4 (with x = 0.2–1). Sample preparation was carried out by mixing the solution of Fe(NO3)3.9 H2O and Ni(NO3)3.6 H2O with egg white, and then the sample was stirred thoroughly using magnetic stirrer. After freeze–drying process, the sample was subjected to calcination treatment and subsequently characterized. The phase composition was evaluated using the X-ray diffraction (XRD) technique, followed by quantitative analysis using Rietveld and Debye-Scherrer Methods. The functionality of the sample was identified using Fourier Transform Infrared (FTIR) spectroscopy, and surface morphology and elemental composition were analyzed using scanning electron microscopycoupled with electron dispersive spectroscopy (SEM/EDS). The results of XRD characterization indicated that materials consist of various crystalline phases, with NiFe2O4 as a major phase. FTIR Analysis revealed the e...

The compounds BaMn2As2 and BaFe2As2 both crystallize in the body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature but exhibit quite different unit cell volumes and very different magnetic and electronic transport properties. Evidently reflecting these disparities, we have discovered a large miscibility gap in the system Ba(MnxFe1-x)2As2. Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples slow-cooled from 1000 • C to room temperature (RT) reveal a two-phase mixture of BaMn2As2 and Ba(Mn0.12Fe0.88)2As2 phases together with impurity phases for x = 0.2, 0.4, 0.5, 0.6 and 0.8. We infer that there exists a miscibility gap in this system at 300 K with composition limits 0.12 < ∼ x < ∼ 1. For samples quenched from 1000 • C to 77 K, the refinements of RT XRD data indicate that the miscibility gap at RT narrows at 1000 • C to 0.2 < ∼ x < ∼ 0.8. Samples with x = 0.4, 0.5 and 0.6 quenched from 1100-1400 • C to 77 K contain a single 122-type phase together with significant amounts of Fe1-xMnxAs and FeAs2 impurity phases. These results indicate that the system is not a pseudo-binary system over the whole composition range and that the 122-type phase has a significant homogeneity range at these temperatures. Magnetic susceptibility χ, electrical resistivity ρ and heat capacity measurements versus temperature T of the single-phase quenched polycrystalline samples with x = 0.2 and 0.8 are reported. We also report attempts to grow single crystals of the substituted compounds Ba(Mn1-xTx)2As2 (T = Cr, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Pt) and BaMn2(As1-xSbx)2 out of Sn flux. Energy dispersive x-ray analyses show that most of these elements do not substitute into the lattice in amounts greater than 0.5%. However, concentrations of 4.4%, ∼ 10% and 2.6% were achieved for Cr, Fe and Sb substitutions, respectively, and χ(T ) and ρ(T ) data for these crystals are presented.

The objective of this work is to present the results of the comparative analysis of YAG:Ce3+ microstructural parameters obtained from x-ray powder diffraction (XRPD) data using Rietveld based Koalariet and Fullprof programs. YAG:Ce3+ powder is obtained via low temperature aerosol route at 3200C followed by post annealing treatment. The chosen technique of synthesis, i.e. ultrasonic spray pyrolysis, provides the generation of spherically shaped and submicronically sized particles having composite nanostructure. Since the targeting garnet phase represents a very promising host phosphor material being doped with rare-earth ions, the most important criteria determining its applicability in various optical devices is the uniform distribution of the luminescent center in the host lattice as well as the cubic YAG phase crystallinity. Comparison of the data obtained for the same samples by the above mentioned XRPD analyses gives us an insight into the validity of the refined parameters.

The mixed rare earth oxide (Dy1‐xErx)2O3 (0.0 ≤ x ≤ 1.0) were synthesized by a sol–gel process. X‐ray and neutron diffraction data were collected and crystal structure and microstructure analyses were performed using Rietveld refinement method. All samples were found to have the same crystal structure and formed solid solutions over the whole range of x. Preferential cationic distribution is found for all samples but with different extent with Dy3+ preferring the 8b among the two non‐equivalent sites 8b and 24d of the space group Ia3. The lattice parameter is found to vary linearly with the composition x and a systematic variation is found in the r.m.s microstrain $ \langle \epsilon^2_{\rm L} \rangle^{1/2} $. Magnetization measurements were done in the temperature range 5‐300 K and a behavior in accordance with Curie‐Weiss law was found. Anomalous concentration dependence is found in magnetic susceptibility which is ascribed to the concentration dependence of effective crystal field...

Polycrystalline La1-x Pb x MnO3±y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of x-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic (FM) phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (β, γ and δ) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of FM clusters. Long-...

Several compounds of the Na2(Mn1–xFex )2Fe(PO4)3 solid solution have been hydrothermally synthesized at 400 °C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld refi nements of the powder X-ray diffraction patterns indicate the presence of Na at the A1 and A2&#39; sites, Mn and Fe at the M1 site, and Mn, Fe, and Fe at the M2 site. The presence of small amounts of Na at the M1 site and Mn at the A1 site indicates a partially disordered distribution of these cations. An excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the M-O vibrations. The Mössbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M1 crystallographic sites. Fe and Fe isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. The derived ir...

The crystal structures of ruthenium oxides with the general formula Nd2−xMxRu2O7−y, where M is Cu or Ag, 0≤x≤0.25, were investigated. All compounds that were prepared exhibit the pyrochlore structure with a cubic unit cell. The compounds were characterized by X-ray powder diffraction, and single-phase structures were found for Nd2−xCuxRu2O7−y, x=0.1, 0.2, 0.25, and for Nd2−xAgxRu2O7−y, x=0.1, 0.15, 0.2. The relative metal concentrations were verified by EDS. The cell parameters were determined by advanced peak-position analysis and calibrated by a Si internal standard. Atomic positions and oxygen occupancies where refined by the Rietveld method. It was found that the cell-size modifications agree with the relations between ionic sizes.

The determination of the mineral composition of aggregates which constitute an important component of concrete is essential to understand and estimate the durability of structures. The modal (quantitative mineralogical) analysis of rocks is generally determined by point-counting method on thin sections or slabs. However, there is a difficulty of mineral identification depending not only on the experience and capability of the operator but also on the size of observable grains. In this study, XRD (X-Ray Diffraction)/Rietveld analysis is proposed as an alternative and a comparison study is performed for eight different rocks. The results show equivalent proportions to those of the point counting method for the major phases (minerals), although discrepancies are observed for the minor minerals. Complementary tests as XRF (X-Ray Fluorescence) and density measurements are also performed to pre-characterize and confirm the obtained modal analysis. For instance, the density calculations based on XRD/Rietveld analysis provide close values to the measured densities. Overall, this method can be an excellent alternative to the point counting method especially in the context of construction materials laboratory.

The article focuses on the stratigraphy of the late Byzantine pavement of the Southwest Church, Umm el-Jimal, Jordan and the production technology of their mortars by applying thin section petrography, x-ray diffractometry (XRD) and scanning electron microscopy with energy dispersive x-ray spectrometry (SEM-EDS). Investigations revealed the similarity between the studied pavement and standard Roman mosaic pavements. The pavement consists of four layers (statumen, rudus, nucleus and bedding), but lacks the tessellatum layer. The statumen was constructed using large stones and then leveled by soil and pebbles, while the other three layers are composed of lime-based mortars formed by two different recipes. The white-beige non-hydraulic mortar of the bedding layer consists of a lime binder and aggregates of scoria and organic fibers, and a Binder:Aggregate (B:A) ratio of 1:2. The grey hydraulic mortars of the rudus and nucleus are mixtures of lime and silica-rich silt/clay, fine sand, volcanic rocks, ceramics, and charcoal; and B:A ratios of 1:4. The rudus and nucleus mortars have high values of hydraulic and cementation indices, reflecting their hydraulic properties, which most probably originated from the reaction between lime, ceramic and volcanic inclusions. In contrast, lack of ceramic and absence of the reactions between lime and scoria of the bedding layer probably produced a mortar with low values of hydraulic and cementation indices, but durable and resistant to weight load.

This research describes the synthesis and characterization of the Pr1.5Eu1.5Ba5Cu8O18 system, obtained by the solid-state reaction method. For the synthesis of this material, oxides of Pr6O11, Eu2O3, BaO and CuO were used. The sintering temperature was 900°C. The structural analysis of the synthesized systems was carried out using X-Ray Diffraction (XRD), with a comparison with theoretical patterns and validated with Rietveld refinement analysis, obtaining a type P2mm crystallographic orthorhombic system with a=3.892454Å, b=3.894411Å and c=31.155851Å. The characterization by means of Scanning Electron Microscopy (SEM) let us conclude that the material presents homogeneous granular morphology. Finally, the magnetic response of this material is determined by the magnetization curves as a function of the applied magnetic field 50K and as a function of temperature 2000Oe.

Systematic investigations of structural properties of 1-10% Fe doped ZnO nanostructure (Fe:ZnO NS) prepared via chemical precipitation method have been reported. Structural properties were probed thoroughly employing scanning electron microscope (SEM) and transmission electron microscope (TEM), energy dispersive X-ray (EDAX) analysis and X-ray diffraction (XRD). Morphological transformation of nanostructures (NS) with Fe incorporation is evident in SEM/TEM images. Nanoparticles (NP) obtained with 1% Fe, evolve to nanorods (NR) for 3% Fe; NR transform to nanocones (NC) (for 5% and 7% Fe) and finally NC transform to nanoflakes (NF) at 10% Fe. Morover, primary phase of Zn 1-x Fe x O along with secondary phases of ZnFe 2 O 4 and Fe 2 O 3 were also revealed through XRD measurements. Based on collective XRD, SEM, TEM, and EDAX interpretations, a model for morphological evolution of NS was proposed and the pivotal role of Fe dopant was deciphered.

In this article, the structural, surface morphology, dielectric and magnetic property of nanoscale Copper ferrite (CFO), synthesized by exploding wire technique (EWT) are studied. The sample is annealed at 650°f or 7 h to remove impurities and defects. The structural analysis of XRD data confirms inverse spinel crystalline structure of average lattice parameter 8.41 Å. The homogenous and fine nanospheres of size varying from micro to nano dimensions are affirmed through micrographs of scanning electron microscopy (SEM). The real part of dielectric constant and dielectric loss (tan d) as a function of frequency are studied. The sample exhibits high values of dielectric constant and dielectric loss in the form of heat at lower frequencies and saturate to lower value at high frequencies. The normal ferromagnetic behaviour of CFO at room temperature is established though magnetic characterization performed by (VSM) vibrating sample magnetometer. The values of remanence, coercivity and maximum obtained magnetization are evaluated.

The copper substituted in LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials are synthesized by the solid state reaction method. Here, we are presenting the details of synthesized LiNi 1/3 Co (1/3-x) Mn 1/3 Cu x O 2 (0, 0.05, 0.1 and 0.15) as an alternative cathode material for lithium-ion batteries. The powder X-ray diffraction (XRD) is used for confirmation of phase formation. Morphology and topography of the materials are investigated through a scanning electron microscope (SEM). The chemical composition is identified by techniques of energy dispersive X-ray spectroscopy (EDS) that is integrated with SEM. The Fourier transform infrared spectroscopy (FT-IR) technique is used to characterize the stretching and bending vibrational modes of different functional groups exist in the materials. At low frequencies, the dispersion of real parts of dielectric constant is due to space charge polarization which is observed for all the temperatures. More over charge/discharge studies are carried out to study the performance of the synthesized cathode materials.

Nanosized zirconia with structural defects was synthesized by using surfactant-templated method. The average crystallite size, phase composition, cationic defect concentration and structural microstrain in the monoclinic phase of zirconia annealed at 800 • C were quantitatively determined by the Rietveld refinement. An unusual behaviour of hydrogen reversibly storing into/releasing from the PdO/ZrO 2 nanophases was observed, which related to formation/decomposition of a hydride phase ␤-PdH 0.76 and to hydrogen storage in the cationic defects of zirconia nanophases by means of hydrogen spillover from Pd metals to zirconia support.

A surfactant-assisted preparation method was successfully used to synthesize the Ce 0.8 Zr 0.2 O 2 nanophases that had homogeneous chemical composition, enhanced thermal stability and improved catalytic activity. Structural refinement by the Rietveld method confirmed that many cationic lattice defects were formed in the ceria-zirconia crystals due to incorporation of the cationic surfactant in the network of the solid. Zirconium dissolving into cubic structure of ceria improved its thermal stability but led to structure distortion. FT-IR in situ characterization showed that CO chemisorption on the palladium loaded ceria-zirconia catalyst formed linear and multibonded CO-metal complexes. It was also evidenced that CO 2 was produced in the CO chemisorption procedure from the pathways of CO disproportionation and CO reacting with lattice oxygen of the catalyst. Owing to high dispersion of the loaded metal palladium and defective structure of the ceria-zirconia support, the Pd/Ce 0.8 Zr 0.2 O 2 catalyst calcined at a temperature range between 873 and 1173 K not only exhibited a more stable catalytic activity for CO oxidation but also performed a lower light-off temperature at cool start below 373 K in comparison with Pd/CeO 2 .

An ordered mesoporous MFI zeolite material (Meso-MFI) was prepared by using CMK-type mesoporous carbons as a hard template. The Meso-MFI exhibits both structural and adsorption differences compared to the conventional bulk MFI zeolite. To study the argon (Ar) adsorption process in Meso-MFI, an in situ gas adsorption powder X-ray diffraction (XRD) analysis was performed using synchrotron X-ray source. Structural rearrangement of the mesoporous MFI zeolite upon Ar adsorption at low temperature (83 K) was intensively studied together with Ar adsorption process in Meso-MFI. We observed that a structural transition of the Meso-MFI zeolite framework from monoclinic (P2 1 /n) to orthorhombic (Pnma) occurred at around 126 Pa at 83 K. Positions of Ar atoms are determined as a function of the Ar gas pressure through Rietveld refinement of powder XRD data. Ar atoms are observed at straight channels, sinusoidal channels, and the intersection of these channels at low pressure. As gas pressure increases, Ar atoms in the pore intersection are pulled off from the intersection toward the straight and sinusoidal channels. The pore shape of the straight channel is changed accordingly with the amount of adsorbed Ar atoms within the pores from circular to oval. These results indicate that Ar adsorption induces not only continuous rearrangement of framework atoms but also symmetry change in the Meso-MFI. A molecular simulation study combined with Rietveld refinement of in situ XRD data provided a full understanding of the adsorption process of Ar in Meso-MFI.

The crystalline structures of superionic high temperature copper selenides Cu 2−x Se (0 ≤ x ≤ 0.25) produced by Mechanical Alloying were investigated using X-ray diffraction (XRD) technique. The measured XRD patterns showed the presence of the peaks corresponding to the crystalline superionic high temperature α-Cu 2 Se phase in the as-milled sample, and its structural data were determined by means of a Rietveld refinement procedure. After a heat treatment in argon at 200 • C for 90 h, this phase transforms to the superionic high temperature α-Cu 1.8 Se phase, whose structural data where also determined through the Rietveld refinement. In this phase, a very low occupation of the trigonal 32(f) sites (∼ 3%) by Cu ions is found. In order to explain the evolution of the phases in the samples, two possible mechanisms are suggested: the high mobility of Cu ions in superionic phases and the intense diffusive processes in the interfacial component of samples produced by Mechanical Alloying.

An approach combining the Rietveld method and pairs distribution function analysis to study crystalline materials under high-pressure and/or temperature was early proposed by us, and in this study, it was applied to investigate de effect of high-pressure on the rhombohedral Bi2Te3 phase. The refined structural parameters obtained from the Rietveld refinement of the XRD patterns measured for pressures up to 9.1 GPa were used as input data to simulate the partial and total structure factors SBi-Bi(K), SBi-Te(K), STe-Te(K), and SBi2Te3(K). Fourier transformation of the Sij(K) factors permitted to obtain the partial and total pairs 2 distribution functions GBi-Bi(R), GBi-Te(R), GTe-Te(R), and GBi2Te3(R). The first coordination shells of these Gij(R) functions are formed by subshells and, with increasing pressure in the 1.1−6.3 GPa range, occur a partial separation of subshells. Also, the increase of pressure in this range promotes a drastic reduction in the values of the intralayer angles Te-BiTe , and consequently, in the intralayer distance Te-Te. A drastic reduction in the interlayers distance Te-Te was also observed. Several studies are reported in the literature, including one carried out by us, show the presence of an ETT in this pressure range. The obtained results suggest that the ETT is related with the decrease of the intralayer angles Te-BiTe , and intra-and interlayer distance Te-Te. Experimental results describing the pressure dependence up to ≈ 6 GPa of the thermoelectric power (S), electrical resistivity (ρ), and power fator (PF) for pure rhombohedral Bi2Te3 and (Bi,Sb)2(Te,Se)3 alloys are reported in the literature, and an enhancement of the power factor in the 1.1−6.3 GPa range is observed. The results obtained in this study give evidence that this enhancement in the power factor is related with the decrease of the intralayer angles Te-BiTe , and with the decrease of intralayer-and interlayers homopolar Te-Te bonds.

A nanostructured trigonal SnSe2 was produced by mechanical alloying, and the effect of high-pressures up to 25.8 GPa on it was investigated. The literature reports refined structural data for SnS2 for pressures up to 20 GPa. These data were used as input data in a crystallographic software to calculate the shell structures around the Sn, Se, and S atoms placed at the origin. The shell structures were used to simulate the partial and total structure factors Sij(K) and S(K), and by Fourier transformation the partial and total pairs distribution functions Gij(R) and G(R) were obtained. The effect of high-pressure on the SnSe2 and SnS2 structures were followed by observing the changes in the Gij(R) functions. Also, the effect of high-pressure on the smallest angle Sn-X (X=Se,S)-Sn, intralayer distance Sn-X (X=Se,S), and interlayers distance X-X (X=Se,S) was studied. The interlayers distance X-X (X=Se,S) changes faster than the intralayer distance Sn-X (X=Se,S). An enhancement of the ave...

The crystalline structures of the superionic high-temperature copper selenides Cu2−x Se (0 &lt; x &lt; 0.25) produced using mechanical alloying were investigated using X-ray diffraction (XRD). The measured XRD patterns showed the presence of peaks corresponding to the crystalline superionic high-temperature α-Cu2Se phase in the as-milled sample, and its structural data were determined by means of a Rietveld refinement procedure. After heat treatment in argon at 473 K for 90 h, this phase transforms to the superionic high-temperature α-Cu1.8Se phase, whose structural data were also determined by Rietveld refinement. In this phase, a very low occupation of the trigonal 32(f) sites (∼ 3%) by Cu ions is found. In order to explain the evolution of the phases in the samples, two possible mechanisms are suggested: (i) the high mobility of Cu ions in superionic phases and (ii) the important diffusive processes in the interfacial component of samples produced by mechanical alloying.