Novel Structure of MgSe in the Multimegabar Regime: Positional Parameter Determination

1997 ◽  
Vol 499 ◽  
Author(s):  
Arthur L. Ruoff ◽  
Ting Li ◽  
Chandrabhas Narayana ◽  
Huan Luo ◽  
Raymond G. Greene
Keyword(s):  
Equation Of State ◽  
Structural Transformations ◽  
Energy Dispersive ◽  
Parameter Determination ◽  
X Ray Diffraction ◽  
X Ray ◽  
Positional Parameter ◽  
Novel Structure ◽  
Diffraction Peaks ◽  
Intensity Calculation

ABSTRACTThe structural transformations in the II-VI compound MgSe have been studied under pressure using energy dispersive x-ray diffraction. MgSe transforms ‘continuously’ from the rocksalt (Bl) structure to a FeSi (B28) or Au-Be structure beginning at 99 ± 8 GPa. At 202 GPa, MgSe is approaching 7-fold coordination with u = 0.0828 and w = 0.4173. The method for intensity calculation of the diffraction peaks is presented. Using the Birch equation, the equation of state to 146 GPa was determined with Bo = 62.8 + 1.6 GPa and Bo′ = 4.1.

A full-pattern fitting algorithm for energy-dispersive X-ray diffraction

2003 ◽  
Vol 36 (5) ◽  
pp. 1123-1127 ◽  
Author(s):  
Yu-Hui Dong ◽  
Jing Liu ◽  
Yan-Chun Li ◽  
Xiao-Dong Li
Keyword(s):  
High Pressure ◽  
Energy Dispersive ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Fitting Algorithm ◽  
Diffraction Angle ◽  
Data Points ◽  
Diffraction Peaks ◽  
Very High

A full-pattern fitting algorithm for energy-dispersive X-ray diffraction is proposed, especially for high-pressure X-ray diffraction studies. The algorithm takes into account the errors in measuring the energy and the diffraction angle. A lognormal function is introduced to represent the background. All the peaks that are detectable in the diffraction spectra, including fluorescence and diffraction peaks, are considered together. Because all the data points in the spectra are used, the accuracy of the cell parameters obtained by this method is very high. This is very helpful in the analysis of the equation of state and the identification of new phases under high pressure.

scholarly journals The suppression of fluorescence peaks in energy-dispersive X-ray diffraction

2014 ◽  
Vol 47 (5) ◽  
pp. 1708-1715 ◽  
Author(s):  
G. M. Hansford ◽  
S. M. R. Turner ◽  
D. Staab ◽  
D. Vernon
Keyword(s):  
Excitation Energy ◽  
Preferred Orientation ◽  
Energy Dispersive ◽  
Source Spectrum ◽  
Natural State ◽  
X Ray Diffraction ◽  
Scattering Angle ◽  
X Ray ◽  
Back Reflection ◽  
Diffraction Peaks

A novel method to separate diffraction and fluorescence peaks in energy-dispersive X-ray diffraction (EDXRD) is described. By tuning the excitation energy of an X-ray tube source to just below an elemental absorption edge, the corresponding fluorescence peaks of that element are completely suppressed in the resulting spectrum. SinceBremsstrahlungphotons are present in the source spectrum up to the excitation energy, any diffraction peaks that lie at similar energies to the suppressed fluorescence peaks are uncovered. This technique is an alternative to the more usual method in EDXRD of altering the scattering angle in order to shift the energies of the diffraction peaks. However, in the back-reflection EDXRD technique [Hansford (2011).J. Appl. Cryst.44, 514–525] changing the scattering angle would lose the unique property of insensitivity to sample morphology and is therefore an unattractive option. The use of fluorescence suppression to reveal diffraction peaks is demonstrated experimentally by suppressing the Ca Kfluorescence peaks in the back-reflection EDXRD spectra of several limestones and dolomites. Three substantial benefits are derived: uncovering of diffraction peak(s) that are otherwise obscured by fluorescence; suppression of the Ca Kescape peaks; and an increase in the signal-to-background ratio. The improvement in the quality of the EDXRD spectrum allows the identification of a secondary mineral in the samples, where present. The results for a pressed-powder pellet of the geological standard JDo-1 (dolomite) show the presence of crystallite preferred orientation in this prepared sample. Preferred orientation is absent in several unprepared limestone and dolomite rock specimens, illustrating an advantage of the observation of rocks in their natural state enabled by back-reflection EDXRD.

CRYSTAL STRUCTURE AND BAND GAP OF RUBIDIUM HYDRIDE TO 120 GPa

1995 ◽  
Vol 09 (18) ◽  
pp. 1133-1140 ◽  
Author(s):  
KOUROS GHANDEHARI ◽  
HUAN LUO ◽  
ARTHUR L. RUOFF ◽  
STEVEN S. TRAIL ◽  
FRANCIS J. DISALVO
Keyword(s):  
Crystal Structure ◽  
Equation Of State ◽  
Band Gap ◽  
Energy Dispersive ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Measurements ◽  
B2 Phase ◽  
Gap Data

Energy dispersive x ray diffraction measurements were performed on RbH to 120 GPa. RbH was observed to transform from the B2 phase to the orthorhombic, CrB, phase at 85 GPa. The equation of state for the B2 phase and the CrB phase are reported. Transmission measurements were made to 120 GPa to determine the band gap versus pressure in RbH. We report here the first measurement of the band gap of RbH at zero pressure at 4.91 eV. At 120 GPa, the band gap closed to 2.68 eV. Extrapolating the present band gap data leads to a zero gap at about 310 GPa.

Influence of Scanning Parameters on X-Ray Diffraction Peaks of Copper

2017 ◽  
Vol 751 ◽  
pp. 202-206
Author(s):  
Parinya Chakartnarodom ◽  
Nuntaporn Kongkajun ◽  
Edward A. Laitila
Keyword(s):  
Statistical Analysis ◽  
Relative Error ◽  
X Ray Diffraction ◽  
Step Size ◽  
X Ray ◽  
Integrated Intensity ◽  
Preset Time ◽  
Diffraction Peaks ◽  
Intensity Calculation ◽  
Statistical Analysis Methods

The aim of this work is to study the influence of x-ray diffractometer scanning parameters on the integrated intensity and full-width at half maximum (FWHM) of copper powder x-ray diffraction peaks by using statistical analysis methods. X-ray diffraction (XRD) analysis of the copper powder was accomplished using step scan mode with step sizes of 0.03o and 0.05o 2q, and preset time changes from 0.1-3.5 s. Integrated intensity of an x-ray peak was calculated by the numerical method. FWHM was measured as the width of Pearson VII model of the x-ray peak at the half-maximum intensity. The statistical analysis methods including linear regression and statistical hypothesis test were used to analyze the correlation between the preset time and the error on integrated intensity calculation, and the FWHM of a peak on the XRD pattern. The results from statistical analysis show that increasing the preset time from 0.1 s to 3.5 s does not affect the FWHM of an x-ray peak, but it reduces the relative error in integrated intensity calculation. Moreover, using the preset time greater than 1 s will minimize the relative error in integrated intensity calculation of an x-ray peak. While step size did not affect both the relative error in integrated intensity calculation or FWHM, the smaller step size would provide more data points for better accurate model of an x-ray peak.

Formation of Cu2ZnSnS4 and Cu2ZnSnS4-CuInS2 Thin Films Investigated by In-Situ Energy Dispersive X-Ray Diffraction

2007 ◽  
Vol 1012 ◽  
Author(s):  
Alfons Weber ◽  
Immo Kötschau ◽  
Susan Schorr ◽  
Hans-Werner Schock
Keyword(s):  
Thin Films ◽  
Reaction Path ◽  
Energy Dispersive ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffusion Effects ◽  
Cuins2 Thin Films ◽  
Diffraction Peaks ◽  
Poor Adhesion

AbstractChalcopyrite CuInS2 and the structurally related kesterite Cu2ZnSnS4 are known as photovoltaic absorber materials. In this study different precursor thin films of the quaternary Cu-Zn-Sn-S system (stacking: Mo/CuS/ZnS-SnS) and of the pentenary Cu-In-Zn-Sn-S system (stacking: Mo/CuIn/ZnS-SnS) were annealed in sulfur atmosphere. The predominant crystalline phases were detected by in-situ energy dispersive X-ray diffraction (EDXRD). Additionally the X-ray fluorescence signals of the film components were recorded to detect diffusion effects. For the quaternary system we found ZnS, CuS, Cu2-xS, Sn2S3 and SnS as main binary phases during annealing. The Sn2S3-SnS phase transition had a significant impact on the later formation of ternary/quaternary phases. A high diffusivity of copper can explain the little influence of the precursor stacking on the reaction path and may also be responsible for the poor adhesion of the films. For annealing temperatures above 450°C Cu2ZnSnS4 can be identified clearly by XRD. The incorporation of indium in the system leads to new diffraction peaks which can be explained by the formation of solid solutions in the system CuInS2-Cu2ZnSnS4.

Control of the phase composition of advanced calcium phosphates using an x-ray diffractometer with a curved position-sensitive detector

2020 ◽  
Vol 86 (6) ◽  
pp. 29-35
Author(s):  
V. P. Sirotinkin ◽  
O. V. Baranov ◽  
A. Yu. Fedotov ◽  
S. M. Barinov
Keyword(s):  
Phase Composition ◽  
Calcium Phosphates ◽  
Position Sensitive Detector ◽  
Sensitive Detector ◽  
X Ray Diffraction ◽  
X Ray ◽  
Impurity Phases ◽  
Position Sensitive ◽  
Diffraction Peaks ◽  
Diffraction Patterns

The results of studying the phase composition of advanced calcium phosphates Ca10(PO4)6(OH)2, β-Ca3(PO4)2, α-Ca3(PO4)2, CaHPO4 · 2H2O, Ca8(HPO4)2(PO4)4 · 5H2O using an x-ray diffractometer with a curved position-sensitive detector are presented. Optimal experimental conditions (angular positions of the x-ray tube and detector, size of the slits, exposure time) were determined with allowance for possible formation of the impurity phases during synthesis. The construction features of diffractometers with a position-sensitive detector affecting the profile characteristics of x-ray diffraction peaks are considered. The composition for calibration of the diffractometer (a mixture of sodium acetate and yttrium oxide) was determined. Theoretical x-ray diffraction patterns for corresponding calcium phosphates are constructed on the basis of the literature data. These x-ray diffraction patterns were used to determine the phase composition of the advanced calcium phosphates. The features of advanced calcium phosphates, which should be taken into account during the phase analysis, are indicated. The powder of high-temperature form of tricalcium phosphate strongly adsorbs water from the environment. A strong texture is observed on the x-ray diffraction spectra of dicalcium phosphate dihydrate. A rather specific x-ray diffraction pattern of octacalcium phosphate pentahydrate revealed the only one strong peak at small angles. In all cases, significant deviations are observed for the recorded angular positions and relative intensity of the diffraction peaks. The results of the study of experimentally obtained mixtures of calcium phosphate are presented. It is shown that the graphic comparison of experimental x-ray diffraction spectra and pre-recorded spectra of the reference calcium phosphates and possible impurity phases is the most effective method. In this case, there is no need for calibration. When using this method, the total time for analysis of one sample is no more than 10 min.

Structural Characterization of Gallbladder Stones Using Energy Dispersive X-ray Spectroscopy and X-ray Diffraction

2018 ◽  
Vol 21 (7) ◽  
pp. 495-500 ◽  
Author(s):  
Hassan A. Almarshad ◽  
Sayed M. Badawy ◽  
Abdalkarem F. Alsharari
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Energy Dispersive ◽  
Spectroscopic Techniques ◽  
X Ray Diffraction ◽  
Major Health Problem ◽  
X Ray ◽  
Gallbladder Stones ◽  
Pure Cholesterol ◽  
Scanning Electron

Aim and Objective: Formation of the gallbladder stones is a common disease and a major health problem. The present study aimed to identify the structures of the most common types of gallbladder stones using X-ray spectroscopic techniques, which provide information about the process of stone formation. Material and Method: Phase and elemental compositions of pure cholesterol and mixed gallstones removed from gallbladders of patients were studied using energy-dispersive X-ray spectroscopy combined with scanning electron microscopy analysis and X-ray diffraction. Results: The crystal structures of gallstones which coincide with standard patterns were confirmed by X-ray diffraction. Plate-like cholesterol crystals with laminar shaped and thin layered structures were clearly observed for gallstone of pure cholesterol by scanning electron microscopy; it also revealed different morphologies from mixed cholesterol stones. Elemental analysis of pure cholesterol and mixed gallstones using energy-dispersive X-ray spectroscopy confirmed the different formation processes of the different types of gallstones. Conclusion: The method of fast and reliable X-ray spectroscopic techniques has numerous advantages over the traditional chemical analysis and other analytical techniques. The results also revealed that the X-ray spectroscopy technique is a promising technique that can aid in understanding the pathogenesis of gallstone disease.

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