rietveld method
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Author(s):  
Alexander M. Sherwood ◽  
Robert B. Kargbo ◽  
Kristi W. Kaylo ◽  
Nicholas V. Cozzi ◽  
Poncho Meisenheimer ◽  
...  

Psilocybin {systematic name: 3-[2-(dimethylamino)ethyl]-1H-indol-4-yl dihydrogen phosphate} is a zwitterionic tryptamine natural product found in numerous species of fungi known for their psychoactive properties. Following its structural elucidation and chemical synthesis in 1959, purified synthetic psilocybin has been evaluated in clinical trials and has shown promise in the treatment of various mental health disorders. In a recent process-scale crystallization investigation, three crystalline forms of psilocybin were repeatedly observed: Hydrate A, Polymorph A, and Polymorph B. The crystal structure for Hydrate A was solved previously by single-crystal X-ray diffraction. This article presents new crystal structure solutions for the two anhydrates, Polymorphs A and B, based on Rietveld refinement using laboratory and synchrotron X-ray diffraction data, and density functional theory (DFT) calculations. Utilizing the three solved structures, an investigation was conducted via Rietveld method (RM) based quantitative phase analysis (QPA) to estimate the contribution of the three different forms in powder X-ray diffraction (PXRD) patterns provided by different sources of bulk psilocybin produced between 1963 and 2021. Over the last 57 years, each of these samples quantitatively reflect one or more of the hydrate and anhydrate polymorphs. In addition to quantitatively evaluating the composition of each sample, this article evaluates correlations between the crystal forms present, corresponding process methods, sample age, and storage conditions. Furthermore, revision is recommended on characterizations in recently granted patents that include descriptions of crystalline psilocybin inappropriately reported as a single-phase `isostructural variant.' Rietveld refinement demonstrated that the claimed material was composed of approximately 81% Polymorph A and 19% Polymorph B, both of which have been identified in historical samples. In this article, we show conclusively that all published data can be explained in terms of three well-defined forms of psilocybin and that no additional forms are needed to explain the diffraction patterns.


2021 ◽  
Vol 16 (3) ◽  
pp. 726-732
Author(s):  
Jayanta Barman ◽  
Archana Das ◽  
Bapan Banik ◽  
Farhana Sultana

Nanocrystalline composite zinc oxide (ZnO) and CdS with Fe doping thin films grown on glass substrate by chemical method. The parameters like temperature of the solution, UV exposure, pH of solution, immersion time, immersion cycles, have been controlled and standardized for nanocrystalline film. The synthesis NPs were analyzed by X-ray diffraction (XRD). Rietveld method shows that Fe-doped composite ZnO/CdS is a single pure phase and wurtzite structure. Samples were analyzed by sophisticated various instrument like XRD, UV- Visible spectrometer, HRTEM, HRSEM and composition was analyzed by EDX attached with HRTEM. The band gap was calculated by absorption spectroscopy and found that absorption was blue-shifted. The electron structure shows that doping changes the crystal structure and transition level create better efficiency and creates octahedral symmetry. The antibacterial studies showed that the 5.0 wt% Fe-doped exhibited maximum antibacterial effect.


2021 ◽  
Vol 8 (4) ◽  
pp. 20218412
Author(s):  
Tatyana S. Spiridonova ◽  
Aleksandra A. Savina ◽  
Evgeniy V. Kovtunets ◽  
Elena G. Khaikina

New compounds of the composition Na5Rb7Sc2(XO4)9 (X = Mo, W) were obtained via the ceramic technology. The sequences of chemical transformations occurring during the formation of these compounds were established, and their primary characterization was performed. Both Na5Rb7Sc2(XO4)9 (X = Mo, W) were found to melt incongruently at 857 K (X = Mo) and 889 K (X = W). They are isostructural to Ag5Rb7Sc2(XO4)9 (X = Mo, W), Na5Cs7Ln2(MoO4)9 (Ln = Tm, Yb, Lu) and crystallize in the trigonal crystal system (sp. gr. R32). The crystal structures were refined with the Rietveld method using the powder X-ray diffraction data. The thermal expansion of Na5Rb7Sc2(WO4)9 was studied by high-temperature powder X-ray diffraction; it was shown that this triple tungstate belongs to high thermal expansion materials.


2021 ◽  
Vol 5 (1) ◽  
pp. 75
Author(s):  
Georgios E. Christidis ◽  
Maria Dimitriadi ◽  
George Triantafyllou ◽  
Christos Tsoumeleas

Six ordinary Portland cement (OPC) clinkers and one white cement clinker were analyzed with the Rietveld method, using ZnO internal standard (IC), to determine the presence of amorphous matter (AM). All clinkers contain abundant AM and have lower silicate phase contents when compared with the same clinkers analyzed without IC, whereas the abundances of the aluminate and ferrate phases were not affected by AM. The white cement clinker had the highest AM content. Determination of AM is important for complete characterization of the OPC clinker and might contribute to a better understanding of the mechanical properties of the clinker.


2021 ◽  
Vol 24 (3) ◽  
pp. 39-48
Author(s):  
Diego Alberto Flores Cano ◽  
Anais Roxana Chino Quispe ◽  
Renzo Rueda Vellasmin ◽  
Joao Andre Ocampo Anticona ◽  
Juan Carlos González ◽  
...  

The Rietveld refinement method has taken high relevance since its creation. Nowadays, it is an useful tool in many fields of industry, materials science, and technology. For these reasons, it becomes a need for scientists and engineers whom pretend to use it for proper analysis of their materials. However, the initiation in the method can be slow, taking into account the accelerated rhythm of the research and economic demands. Thus, this work is an intend to fulfill this hole, providing the basic foundations and methodology of the Rietveld refinement in a brief way, this along with the results of its application in superconducting samples of Yttrium Barium Copper Oxide and magnesium diboride, and functional magnetic nanoadsorbents of maghemite and a multiphasic composite (iron oxide, hydroxyapatite and secondary phases). In the process, an in-detail protocol was designed and provided. It was concluded that the samples were successfully refined and that this work represents a fast introduction to the Rietveld method for which beginners can obtain good results while making correct interpretations ofthe whole refinement process.


2021 ◽  
Vol 105 (1) ◽  
pp. 143-149
Author(s):  
Jan Smejkal ◽  
Ladislav Chladil

Our contribution deals with the study of surface processes and chemical composition on the surface of the negative electrode of a lead-acid battery during cycling at different speeds. Thin electrodes were created for the measurements. The negative electrode was analyzed at six SOC states (100 %, 80 %, 60 %, 40 %, 20 % and 0 % SOC). The proportion of individual elements on the surface of the negative electrode during cycling at 0.2 C, 0.3 C and 0.5 C was evaluated. Chemical changes occurring on the surface of the negative electrode during cycling of the lead-acid battery were measured using an X-ray diffractometer, and the presence of individual chemical elements on the surface of the electrode was evaluated using the Rietveld method. At higher cycling speeds, an increase in the material was observed, which did not convert during cycling, and higher cycling speeds caused a more significant material conversion near the negative electrode collector.


Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1320
Author(s):  
Sytle M. Antao

The crystal structure of two different samples of pyrope garnet, ideally Mg3Al2Si3O12, from South Africa was refined using the Rietveld method, space group Ia3¯d, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Sample 1 from Wesselton Mine is a single cubic phase and is optically isotropic. Electron-probe microanalysis (EPMA) provided an average composition {Mg2.30Fe2+0.26Ca0.42Mn2+0.02}∑3[Al1.53Fe3+0.06Cr3+0.40Ti4+0.01Fe2+0.01]∑2Si3O12, which contains a significant amount of Cr cations. The unit-cell parameter (Å) and bond distances (Å) are a = 11.56197(1) Å, average <Mg-O> = 2.2985, Al-O = 1.9101(4), and Si-O = 1.6343(3) Å. Sample 2 from De Beers Diamond Mine has an average composition {Mg2.33Fe2+0.33Ca0.33Mn2+0.01}∑3[Al1.73Fe3+0.12Cr3+0.06Ti4+0.05Fe2+0.05]∑2Si3O12 and is a fine-scale intergrowth of two cubic phases. The weight percentage, unit-cell parameter (Å), and bond distances (Å) for phase 2a are 62.2(1)%, a = 11.56185(1) Å, average <Mg-O> = 2.3006, Al-O = 1.9080(4), Si-O = 1.6334(4) Å. The corresponding values for phase 2b are 37.8(1)%, a = 11.53896(1) Å, average <Mg-O> = 2.2954, Al-O = 1.9020(6), Si-O = 1.6334(6) Å. The two cubic phases in sample 2 cause the crystal to be optically anisotropic because of strain induce birefringence. The unit-cell parameter and bond distances for sample 1 are similar to those in phase 2a.


Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6953
Author(s):  
Inés R. Salcedo ◽  
Ana Cuesta ◽  
Shiva Shirani ◽  
Laura León-Reina ◽  
Miguel A. G. Aranda

Cement hydration is a very complex set of processes. The evolution of the crystalline phases during hydration can be accurately followed by X-ray powder diffraction data evaluated by the Rietveld method. However, accurate measurements of some microstructural features, including porosity and amorphous content developments, are more challenging. Here, we combine laboratory X-ray powder diffraction and computed microtomography (μCT) to better understand the results of the μCT analyses. Two pastes with different water–cement ratios, 0.45 and 0.65, filled within capillaries of two sizes, ϕ = 0.5 and 1.0 mm, were analysed at 50 days of hydration. It was shown that within the spatial resolution of the measured μCTs, ~2 μm, the water capillary porosity was segmented within the hydrated component fraction. The unhydrated part could be accurately quantified within 2 vol% error. This work is a first step to accurately determining selected hydration features like the hydration degree of amorphous phases of supplementary cementitious materials within cement blends.


Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1841
Author(s):  
Edgar Pio ◽  
Ariosto Medina ◽  
Carola Martínez ◽  
Felipe Manuel Castro Cerda ◽  
Claudio Aguilar

Four titanium alloys (Ti-Ta, Ti-Ta-Sn, Ti-Ta-Mn, and Ti-Nb-Sn) were synthesized by mechanical alloying (MA) in a planetary mill in different times between 2 h and 100 h. The microstructure characterization was made by X-ray diffraction (XRD), in which the Rietveld method was applied to analyze the diffraction patterns. The study demonstrated that after short milling times between 2 h and 30 h, the fraction of hexagonal close-packed (hcp) phase decreases; at the same time, the formation of body-centered cubic (bcc) and face-centered cubic (fcc) Ti phases are promoted. Additionally, after 30 h of MA, the full transformation of hcp-Ti was observed, and the bcc-Ti to fcc-Ti phase transformation took place until 50 h. The results suggest that the addition of Ta and Sn promotes the fcc-Ti phase formation, obtaining 100% of this phase at 50 h onwards, whereas Nb and Mn show the opposite effect.


Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1178
Author(s):  
Uwe König

Nickel laterite ore is used to produce nickel metal, predominantly to manufacture stainless steel as well as nickel sulfate, a key ingredient in the batteries that drive electric vehicles. Nickel laterite production is on the rise and surpassing conventional sulfide deposits. The efficiency of mining and processing nickel laterites is defined by their mineralogical composition. Typical profiles of nickel laterites are divided into a saprolite and a laterite horizon. Nickel is mainly concentrated and hosted in a variety of secondary oxides, hydrous Mg silicates and clay minerals like smectite or lizardite in the saprolite horizon, whereas the laterite horizon can host cobalt that could be extracted as a side product. For this case study, 40 samples from both saprolite and laterite horizons were investigated using X-ray diffraction (XRD) in combination with statistical methods such as cluster analysis. Besides the identification of the different mineral phases, the quantitative composition of the samples was also determined with the Rietveld method. Data clustering of the samples was tested and allows a fast and easy separation of the different lithologies and ore grades. Mineralogy also plays a key role during further processing of nickel laterites to nickel metal. XRD was used to monitor the mineralogy of calcine, matte and slag. The value of mineralogical monitoring for grade definition, ore sorting, and processing is explained in the paper.


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