Papers by Keyword: Rietveld Refinement

Abstract: This study explores the phase and structural transformations of new lanthanum substituted sodium lead phosphate composite, Pb_(8-x)La_xNa₂(PO₄)₆ with x=0.00 to 0.30. The main focus is to establish the limits of substitution of La³⁺ in the apatite lattice and to understand its effect after substitution. The apatite composite specimen was prepared through a solid–state reaction at 830 °C and characterized using Rietveld–XRD, FT IR and SEM techniques. The statistics suggest that the structure mostly remains a constant up to x = 0.20. However, when the amount of lanthanum exceeds the limit, secondary phases exist and become dominant showing the limit of lanthanum entry. The insertion leads to changes in the host-cation lattice; namely a nonlinear variation along the a-axis, while there is a linear variation along the c-axis in lead-apatite. FT-IR data further confirms that PO₄³⁻ is a tetrahedral ion in the structure. Microstructure is more densely packed what is new in this work is the study of the structural changes which lead to the formation of larger amounts of lead-apatite composites with a wider range of La³⁺ range. The structural changes seen in this study shed light on the structural changes that must occur for effective integration of lead-apatite composites. A fresh perspective on how this study contributes to your submission.

Abstract: This article reports the study of photoluminescence spectra of Di Strontium Magnesium Silicate (Sr₂MgSi₂O₇) doped with various concentration of Europium (Eu³⁺) prepared using solid-state reaction technique. The doping concentration (s) of Eu3+ were 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 mol% respectively. Excitation spectrum monitored at 620 nm wavelength that exhibited two prominent peaks centered at 256 nm and 277 nm. Peak observed at 277 nm was more intense therefore the emission spectra were monitored at 277. Emission Spectra of all the samples revealed intense peaks centred at 607, 618 and 637 are attributed to ⁵D₀ ⁷F₂ of Europium (III) ions accommodated at various lattice sites having different energies. Overall emission was found in the red colour region which was confirmed using a CIE chromaticity diagram with coordinate (0.4805, 0.3763). Critical distance for energy transfer in the concentration, beyond which concentration quenching occurred in PL spectra, was calculated. In this case, the critical distance was found to be 19.87 Å, therefore the mechanism involved in concentration quenching of Sr₂MgSi₂O₇ doped with 2.0 mol % of Europium (III) must be only multipole-multipole exchange whereas the exchange interaction is ineffective.

Abstract: The paper studies the geometric optimization and elastic moduli of Ca₂₄Si₂₂O₅₂(OH)₁₆(H₂O)₂₈ supercells with 28 water molecules embedded at different degree angles. The water molecule embedment in the supercell is performed by the molecule rotation about X, Y and Z axes to the required angle. It is shown that the position of water molecules significantly affects the internal energy, elastic properties and stability of the optimized supercell and the geometry of its crystal lattice. Supercells with water molecules embedded at 2, 4, 20, 80, 300, 354 and 356-degree angles are stable structures, and a supercell with water molecules embedded at a 20-degree angle turns to be much more stable. The refined structural parameters, lattice volumes, elastic moduli, and atom positions are determined for the geometrically optimized supercell states. Stable supercells can be included in Richardson’s crystallographic database with a view to use them as the reference standards in the Rietveld refinement of the structural properties of hydrated Portland cement with variable water content.

Abstract: Powder nanoparticles of vanadium oxide doped with titanium dioxide were successfully prepared by the chemical co-precipitation method. The sample was calcined at temperatures 150, 300, 450, and 600°C. As prepared and heat-treated samples were structurally characterized through X-ray diffraction. The crystal size, cell parameters, R-Factor, and structural properties of mixed nano oxide were investigated. The value of the goodness fit factor, R-Factor, and cell parameters were examined by Rietveld Refinement. XRD study reveals that V₂O₅ exhibits orthorhombic structure and this orthorhombic phase is fully developed at 600°C. By using XRD data crystallite size of V₂O₅ was estimated to be 33.98nm and the crystallite size of TiO₂ was estimated to be 35.04nm.

Abstract: Li₇La₃ZrSnO₁₂ was successfully prepared by conventional solid-state synthesis. Diffraction data show that the prepared sample has a mixture of two different phases. Both phases have tetragonal crystal symmetry but two different space groups, which are I41/acd and I4/mmm. Rietveld refinements were performed by using the models of the initial structures based on Li₇La₃Zr₂O₁₂ (I41/acdz) and Li₇La₃Ce₂O₁₂ (I4/mmm). It used to quantify the ratio between those two phases by employing Relative Intensity Ratio (RIR) technique. Crystal structure analysis showed that atomic arrangement in Li₇La₃Zr₂O₁₂ (I41/acdz) has more connected 3D tunnel for Li ions migration compared to Li₇La₃Ce₂O₁₂ (I4/mmm) that only connected tunnel at the edge of unit cell. Therefore, the existence of tetragonal phase with the space group of I4/mmm may resulting low ionic conductivity of Li ions at room temperature.

Abstract: This article presents a comparative study between the ZnO nanocone and nanofibers. ZnO nanocones were synthesized through the green route, using Azadirachta indica leaf extract media, and ZnO nanofibers were synthesized by the electrospinning process. The microstructural parameters of the prepared nanomaterials were investigated using powder X-ray diffractometer (XRD) and Rietveld refinement analysis. The XRD patterns confirmed the formation of single-phase ZnO with hexagonal wurtzite structure having an average crystallite size of 21 nm and 54 nm for the conical and fibrous nanoparticles, respectively. The field emission scanning electron microscopy revealed that the mean radius of nanofibers was 25-30 nm while the mean height and mean base radius of nanocones were 181 nm and 91 nm respectively. Elastic properties were estimated using elastic compliances S₁₁ (6.0678×10^-12 m²N^-1), S₁₂ (-2.2602×10^-12 m²N^-1), S₁₃ (-1.3579×10^-12 m²N^-1), S₃₃ (5.5196×10^-12 m²N^-1) and S₄₄ (22.6833×10^-12 m²N^-1) which were calculated using the THERMO-PW code, based on the density functional theory. The calculated elastic constants of the two nanostructures yielded similar values as expected. However, the elastic limit of the two nanostructures differs due to their morphological anomaly. Moreover, the optical bandgap of nanofibrous ZnO was lower than that of nanoconical ZnO.

Abstract: A modified sol-gel method using metal nitrate salts was adopted to synthesis proton conductor of Ba(Ce_1-xZr_x)_0.95Yb_0.05O_2.975 where x=0.2, 0.3, 0.4, 0.5 and 0.6 ceramic powders. The aim of this work is to study the crystal structure of Yb-doped barium cerate solid solution at different Zr concentrations. The powder was calcined at 1100°C for 12 hours and pressed at 5 tons to become a pellet by a dry pressing technique. The pellet was sintered at 1400°C in air for 6 hours and ground to powder form prior to the X-ray diffraction measurement. The raw diffraction data of the sample at room temperature was analyzed using Rietveld refinement method in X’pert Highscore software. Cubic crystal structure was observed by software with goodness of fit in average 2.82. Phase formation, structure analysis and the empirical rule which holds the linear relation between lattice parameters at different Zr concentrations using Vegard’s Law were also presented and discussed.

Abstract: Composite solid propellants are preferred for use in defense and space applications because of their high energy density and simplicity. Oxidizers take up the highest percentage in propellant ingredient. KNO₃, KClO₄ and K₂Cr₂O₇ are among the inorganic oxidizers with similar cation for present study, and their chemical and physical properties are fully understood. However, the relationship between thermal stability and electrostatic potential energy based on structural analysis has not yet been studied. In this study we used high resolution XRD data to study the electrostatic potential energy of the KNO₃, KClO₄ and K₂Cr₂O₇ crystal structures.

Abstract: A perovskite manganate material La_0,667Ba_0,333Mn_1-xCu_xO₃ (x = 0.35 and 0.40) were prepared. The samples were synthesized by sol gel method. The samples were sintered at 1000^OC for 6 hours. Rietveld refinement shows that both samples are crystallized in orthorhombic structure with Pnma space group. This results is in accordance with Goldschmidt’s tolerance factor value which are 0.8698 and 0.8701 for x = 0.35 and 0.4, respectively. Subtitutions with large amount of copper ions in B-sites caused the unit cell to decrease from 236.234 ų to 236.088 ų . Futher calculation from crystallography Refinement also shows that copper subtitutions increase the crystallite size of the samples from 74.8 nm to 94.49 nm. It has been found from the SEM results that copper subtitutions also alter the morphology of the samples.

Abstract: Nd₁(Fe)_0.2Ba_1.8Cu₃O_7-δ oxide material have been successfully synthesized by solid-state reaction with modified heat treatment process to improve the heat time efficiency, calcination at 950°C for six hours, sintering at 975°C fo six hours, and annealing at 450°C for six hours, respectively. The X-ray diffraction pattern shows that a single-phase form of Nd₁(Fe)_0.2Ba_1.8Cu₃O_7-δ is an orthorhombic (Pmmm) structure. The Rietveld refinement analysis found, the lattice parameter are a = 3.8758Å, b = 3.9101Å, and c = 11.7190Å with χ² = 1.394%. The SEM-EDAX image shows that the samples are form clusters with size estimates of 10 - 40μm, and the elemental composition of the oxide materials is Ba rich.