scholarly journals Structural, optical and electronic characteristics of non-stoichiometric nano cadmium sulfide

2021 ◽  
Author(s):  
Zein K. Heiba ◽  
Mohamed Bakr Mohamed ◽  
Noura M. Farag ◽  
Ali Badawi
Keyword(s):  
Rietveld Method ◽  
Cadmium Acetate ◽  
Rietveld Analysis ◽  
Excitation Wavelength ◽  
Sulfur Deficiency ◽  
The Matrix ◽  
Microstructure Parameters ◽  
Microscope Imaging ◽  
Infrared Spectrometer ◽  
Oxygen Substitution

Abstract Samples of non-stoichiometric nano CdS1 − x were synthesized by a simple thermolysis method by lowering the ratio of thiourea relative to cadmium acetate as starting precursors; Cd(Ac):(1-x) thiourea (x = 0.0, 0.03, 0.05 and 0.1). X’pert HighScore Plus program manifested biphasic CdS (cubic and hexagonal) and the Rietveld analysis was utilized to match the structural and microstructure parameters of the formed samples. The possibility of formed CdS1 − xOx alloy due to the sulfur deficiency is also examined using the Rietveld method. A High-resolution transmission electron microscope imaging exhibited nano size particles with homogeneous morphology. Fourier transform infrared spectrometer was utilized to confirm the existence of O2 in CdS1 − x matrix. The bandgap energies for CdS1 − x are reduced below the values of energy gaps of CdS and CdO upon increasing the parameter (x) forming a band gap “bowing”. The photoluminescence (PL) emitted visible colors depending on the amount of sulfur deficiency and excitation wavelength used. The maximum PL intensity observed in CdS0.9 sample, confirmed the presents of oxygen inside the matrix. The influence of oxygen substitution or vacancies of sulfur on the electronic structure and optical features of CdS was also investigated applying density function calculations.

scholarly journals Iron-chromium-carbon-vanadium white cast irons: Microstructure and properties

2014 ◽  
Vol 68 (4) ◽  
pp. 413-427 ◽  
Author(s):  
Mirjana Filipovic
Keyword(s):  
Fracture Toughness ◽  
Strain Hardening ◽  
Volume Fraction ◽  
Dynamic Fracture Toughness ◽  
M23c6 Carbide ◽  
Cast Irons ◽  
Repeated Impact ◽  
Secondary Carbides ◽  
The Matrix ◽  
Microstructure Parameters

The as-cast microstructure of Fe-Cr-C-V white irons consists of M7C3 and vanadium rich M6C5 carbides in austenitic matrix. Vanadium changed the microstructure parameters of phase present in the structure of these alloys, including volume fraction, size and morphology. The degree of martensitic transformation also depended on the content of vanadium in the alloy. The volume fraction of the carbide phase, carbide size and distribution has an important influence on the wear resistance of Fe-Cr-C-V white irons under low-stress abrasion conditions. However, the dynamic fracture toughness of Fe-Cr-C-V irons is determined mainly by the properties of the matrix. The austenite is more effective in this respect than martensite. Since the austenite in these alloys contained very fine M23C6 carbide particles, higher fracture toughness was attributed to a strengthening of the austenite during fracture. Besides, the secondary carbides which precipitate in the matrix regions also influence the abrasion behaviour. By increasing the matrix strength through a dispersion hardening effect, the fine secondary carbides can increase the mechanical support of the carbides. Deformation and appropriate strain hardening occur in the retained austenite of Fe-Cr-C-V alloys under repeated impact loading. The particles of precipitated M23C6 secondary carbides disturb dislocations movement and contribute to increase the effects of strain hardening in Fe-Cr-C-V white irons.

scholarly journals Rietveld Method Applied for Triacylglycerol Polymorphism Analysis

2014 ◽  
Vol 70 (a1) ◽  
pp. C1764-C1764
Author(s):  
Guilherme Calligaris ◽  
Ana Paula Ribeiro ◽  
Adenilson dos Santos ◽  
Lisandro Cardoso
Keyword(s):  
Rietveld Method ◽  
Rietveld Analysis ◽  
Polymorphic Form ◽  
Polymorphism Analysis ◽  
X Ray Diffraction ◽  
Full Characterization ◽  
Β Phase ◽  
Lack Of Information ◽  
Refinement Method

The characterization of the fat components becomes very useful in the formulation of shortening, margarines and fatty products due to their unique properties of plasticity, texture, solubility and aeration. The qualitative analysis obtained by X-ray diffraction (XRD) can be further improved in order to fulfill the lack of information on the triacylglycerol (TAG) in the hardfat systems aiming a complete polymorph characterization. In this work, as an attempt to quantify the distinct β and β' TAG polymorphs, XRD was combined with Rietveld refinement method and applied to two types of samples: mixtures (M) and blended hardfats (B) samples involving fully hydrogenated of soybean (FHSO) and palm (FHPO) oils. M-samples were prepared with linear concentrations of FHSO (β) and FHPO (β') and their Rietveld analysis have provided the expected content trend through the involved polymorphic phases with a very good agreement (~5%). This result validates the Rietveld method applicability on this kind of materials. The Rietveld method applied for B-samples has shown that β' polymorphic form prevails over the β-form, even for samples originally prepared with FHSO (β)/FHPO (β') = 60/40 ratio (see figure). This result indicates the influence of the seeding process (earlier crystallization of β' phase). This first quantitative approach for blended samples represents a very useful contribution towards the full characterization of fats.

Quantitative Analysis of Cement-Based Materials and Sulfate Attack Products by XRD-Rietveld Analysis

2013 ◽  
Vol 357-360 ◽  
pp. 1362-1369 ◽  
Author(s):  
Hua Li ◽  
Jia Ping Liu ◽  
Wei Sun
Keyword(s):  
Quantitative Analysis ◽  
Calcium Hydroxide ◽  
Rietveld Method ◽  
Internal Standard ◽  
Rietveld Analysis ◽  
Sulfate Attack ◽  
Practical Significance ◽  
Cement Pastes ◽  
Cement Based Materials ◽  
Mixed Samples

XRD-Rietveld method has been adopted for quantitative analysis of phases in cement powder, phases in mixed samples of cement and pure calcium hydroxide, and sulfate attack products in cement pastes, based on the TOPAS software. The results show that, Rietveld analysis values show good agreement with the actual levels of mixed samples, and the accuracy degree of Rietveld method is at least as well as that of TG/DSC method which is commonly used in quantitative analysis of calcium hydroxide. By adding appropriate internal standard substance, XRD-Rietveld analysis method can be effectively used in quantitative analysis of sulfate attack products in cement-based materials. This work has practical significance on the study of sulfate attack of cement-based material.

Structure of Carbonated Hydroxyapatite Based on Rietveld Method

2008 ◽  
Vol 368-372 ◽  
pp. 1187-1189
Author(s):  
Xu Ran ◽  
Jun Guo Ran ◽  
Li Gou ◽  
Ji Yong Chen ◽  
Jiao Min Luo
Keyword(s):  
Crystal Structure ◽  
Sintering Temperature ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Structure Parameters ◽  
X Ray Diffraction ◽  
Carbonated Hydroxyapatite ◽  
X Ray ◽  
Quantitative Results ◽  
Distortion Index

The crystalline structures of B-type carbonated hydroxyapatite (CHA) powders sintered at 700, 900 and 1100°C, respectively, were studied by Rietveld analysis of powder X-ray diffraction (XRD) data. A series of structure parameters, including lattice parameters (a and c), bond length and the distortion index of PO4 tetrahedron (Dind) were calculated by Rietveld method to characterize the fine structure of CHA. The broadening effect of XRD reflections was separated to calculate the micro-strain and crystalline size. The results showed that CHA become more stable with the increase of sintering temperature, but the CO3 2- is almost lost at temperature of 1100°C. The quantitative results about crystal structure of CHA based on crystalline structure simulated by Rietveld method are obtained.

scholarly journals Quantitative Phase Analysis of Skarn Rocks by the Rietveld Method Using X-ray Powder Diffraction Data

Minerals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 894
Author(s):  
Yana Tzvetanova ◽  
Ognyan Petrov ◽  
Thomas Kerestedjian ◽  
Mihail Tarassov
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Quantitative Phase Analysis ◽  
Chemical Compositions ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Fine Grained ◽  
Variable Chemical

The Rietveld method using X-ray powder diffraction data was applied to selected skarn samples for quantitative determination of the present minerals. The specimens include garnet, clinopyroxene–garnet, plagioclase–clinopyroxene–wollastonite–garnet, plagioclase–clinopyroxene–wollastonite, plagioclase–clinopyroxene–wollastonite–epidote, and plagioclase–clinopyroxene skarns. The rocks are coarse- to fine-grained and characterized by an uneven distribution of the constituent minerals. The traditional methods for quantitative analysis (point-counting and norm calculations) are not applicable for such inhomogeneous samples containing minerals with highly variable chemical compositions. Up to eight individual mineral phases have been measured in each sample. To obtain the mineral quantities in the skarn rocks preliminary optical microscopy and chemical investigation by electron probe microanalysis (EPMA) were performed for the identification of some starting components for the Rietveld analysis and to make comparison with the Rietveld X-ray powder diffraction results. All of the refinements are acceptable, as can be judged by the standard indices of agreement and by the visual fits of the observed and calculated diffraction profiles. A good correlation between the refined mineral compositions and the data of the EPMA measurements was achieved.

scholarly journals Study of selection and purification of Brazilian bentonite clay by elutriation: a XRF, SEM and Rietveld analysis

Cerâmica ◽  
2016 ◽  
Vol 62 (361) ◽  
pp. 1-8 ◽  
Author(s):  
J. L. Alves ◽  
A. E. Zanini ◽  
M. E. de Souza ◽  
M. L. F. Nascimento
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Rietveld Method ◽  
Bentonite Clay ◽  
Rietveld Analysis ◽  
Industrial Applications ◽  
X Ray Diffraction ◽  
X Ray ◽  
Almost All ◽  
Scanning Electron

Abstract Clays obtained from nature have a lot of impurities. Therefore, for best using of these materials, it is necessary its selection and purification. Thus, the aim of this work is to separate and to purify the smectite fractions using water as a solvent at a low flux mixed with a bentonite clay extracted from a mine in Vitória da Conquista - Bahia / Brazil. For this a separation method of fractions of expandable clays based on the Stokes' Law was applied - this process is called elutriation, in order to ensure and to expand possible industrial applications of this material. The samples were characterized by analysis of X-ray diffraction, X-ray fluorescence and scanning electron microscopy. The Rietveld method enabled the quantification of main phase minerals: montmorillonite, kaolinite, nontronite and quartz, reaching 85% in mass of montmorillonite phase at the end of the process. Results showed that the method used was efficient to remove almost all quartz, carbonates and organic matter from the sample. It was also observed a monomodal grain size distribution of elutriated materials with thinner grains, around (18.1 ± 1.8) μm at the end of the process. It has been concluded that the method developed and applied showed promising characters to be applied to elutriate kilograms of clays and could be used in industrial scale.

Microstructure of Pyrolytic Carbon Matrix in Carbon/Carbon Composites after Graphitization

2007 ◽  
Vol 336-338 ◽  
pp. 1270-1273 ◽  
Author(s):  
Wan Chang Sun ◽  
He Jun Li ◽  
Shou Yang Zhang ◽  
Yong Huang
Keyword(s):  
Polarized Light ◽  
Carbon Matrix ◽  
Pyrolytic Carbon ◽  
Interplanar Distance ◽  
Carbon Composites ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Before And After ◽  
The Matrix ◽  
Microstructure Parameters

The morphologies and textures of the pyrolytic carbon matrix in 2D-C/C composites after graphitization were investigated by means of polarized light microscope (PLM) and high resolution transmission electron microscope (HRTEM). The microstructure parameters of the pyrolytic carbon matrix before and after graphitization were characterized with X-ray diffraction (XRD) technology. It was found that the interplanar distance of (002) planes (d002) of pyrolytic carbon matrix decreases, and the microcrystalline stack height (LC) increases after graphitization. Graphitization treatment resulted in a coarsening of the surface texture and in the formation of circumferential cracks within the matrix. The lattice fringes of the pyrolytic carbon matrix are continuous and longer in each domain and the (002) peak spot is smaller and more intense after graphitization.

A semi-empirical asymmetry function for X-ray diffraction peak profiles

1995 ◽  
Vol 10 (3) ◽  
pp. 204-206 ◽  
Author(s):  
P. Riello ◽  
P. Canton ◽  
G. Fagherazzi
Keyword(s):  
Goodness Of Fit ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Opening Angle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Asymmetry Function ◽  
The Asymmetry ◽  
Fit Index ◽  
Semi Empirical

A new semi-empirical approximation for the asymmetry function to be used in the X-ray Rietveld analysis has resulted in lower values of the so-called goodness-of-fit index, defined as S = Rwp/Rexp, where Rwp is the R-weighted pattern and Rexp is the R-expected [R. A. Young, The Rietveld Method (Oxford U.P., Oxford, 1993)], with respect to the corresponding values obtained with the classical approximation used by Rietveld in his fundamental paper. A comparing test of the two asymmetry functions was carried out for the cubic Y2O3 and for αAl2O3 using either pseudo-Voigt or Pearson VII symmetrical functions and two diffractometers. As in the case of the Rietveld approximation, the present one, which employs an exponential function, is optimized using only one fitting parameter. Experimentally, the asymmetry can be considerably diminished by using Soller slits with a small opening angle (≤2°).

Effects of Thermal Treatment on the Structure of Eu:YAG Nanopowder

2007 ◽  
Vol 128 ◽  
pp. 107-114 ◽  
Author(s):  
Maria Luisa Saladino ◽  
Eugenio Caponetti ◽  
Stefano Enzo
Keyword(s):  
Thermal Treatment ◽  
Lattice Strain ◽  
Rietveld Method ◽  
Lattice Parameter ◽  
Spherical Particles ◽  
X Rays ◽  
Garnet Phase ◽  
The Matrix ◽  
Different Temperatures ◽  
Co Precipitation

Eu:YAG nanopowder precursors were obtained by co-precipitation of aluminium, yttrium and europium nitrates solution with ammonia. The hydroxides precursors were calcined at different temperatures from 900 to 1200°C as a function of holding time (1, 2 and 6 hours). The presence of Eu3+ ions in the matrix was confirmed by Energy Dispersive X-rays analysis. X-Ray Diffraction investigation by the Rietveld method shows that the sample treated at 900°C for 1 hour is essentially the garnet phase with the minor presence of hexagonal and monoclinic metastable phases. The Eu3+ ions are incorporated into the garnet phase, as is suggested by the lattice parameter value being larger than that in literature data (homogeneous strain). For the sample treated at 900°C for 1 hour, electron microscopy observations showed agglomerates of spherical particles of mean size about 50 nm. At higher temperature treatments and for longer holding times the minority hexagonal and monoclinic phases totally disappeared. However, the lattice parameters of the cubic garnet phase gradually decreased with temperature, suggesting an expulsion of Eu3+ ions from the solid solution. Simultaneous with this, it was noted that the lattice strain reached a maximum value, but to later decrease, due to the vacancies created by the Eu species initially migrating to the surface of the coherent domains of diffraction. The lattice strain definitely decreased upon more drastic thermal treatments. Meanwhile, FEG-SEM and TEM observations on the same samples confirmed the growth of the garnet particles as a function of the thermal treatment.

Observation of orientational disorder in the hexagonal stuffed tridymite Sr0.864Eu0.136Al2O4by the maximum-entropy method

2004 ◽  
Vol 37 (5) ◽  
pp. 698-702 ◽  
Author(s):  
H. Yamada ◽  
W. S. Shi ◽  
C. N. Xu
Keyword(s):  
Maximum Entropy ◽  
Electron Density ◽  
Maximum Entropy Method ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Atomic Displacement ◽  
Entropy Method ◽  
Apical Oxygen ◽  
Threefold Axis ◽  
Density Image

The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gaveRwp= 2.99% andRB= 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased theRfactors toRwp= 2.81% andRB= 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along thecaxis. These results suggest that AlO4tetrahedra in Sr0.864Eu0.136Al2O4are orientationally disordered.

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