scholarly journals Формирование структуры гексагонального алмаза: ab initio расчеты

2019 ◽  
Vol 61 (10) ◽  
pp. 1926
Author(s):  
Е.А. Беленков ◽  
В.А. Грешняков
Keyword(s):  
Uniaxial Compression ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Density Functional Theory Method ◽  
Microscopic Analysis ◽  
Hexagonal Structure ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
Hexagonal Diamond ◽  
Molecular Layers

Modeling of the structure formation of hexagonal diamond from graphite and cubic diamond was performed using the density functional theory method. The transformation of orthorhombic AB graphite into hexagonal diamond can occur as a result of uniaxial compression at pressures above 61 GPa. For the formation of hexagonal diamond from AA graphite, the pressure must exceed 57 GPa. Another possible way to obtain hexagonal diamond is uniaxial compression of cubic diamond at pressures from 300 to 380 GPa. The data of theoretical calculations were used to interpret the diffraction data obtained as a result of X-ray diffraction and electron microscopic analysis of natural and synthetic diamond-like materials. It was found that crystals with the ideal cubic and hexagonal structure are not contained in diamond-like carbon materials, and their structure is characterized by random packing of molecular layers.

Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculations

2009 ◽  
Vol 65 (5) ◽  
pp. 639-646 ◽  
Author(s):  
Edward E. Ávila ◽  
Asiloé J. Mora ◽  
Gerzon E. Delgado ◽  
Ricardo R. Contreras ◽  
Luis Rincón ◽  
...  
Keyword(s):  
Solid State ◽  
Diffraction Data ◽  
Density Functional ◽  
Simulated Annealing Algorithm ◽  
Theoretical Calculations ◽  
Tight Binding ◽  
Van Der Waals Interactions ◽  
Am1 Calculations ◽  
X Ray Diffraction ◽  
X Ray

The molecular and crystalline structure of ethyl 1′,2′,3′,4′,4a′,5′,6′,7′-octahydrodispiro[cyclohexane-1,2′-quinazoline-4′,1′′-cyclohexane]-8′-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006). J. Appl. Cryst. 39, 910–915] was obtained performing a conformational study on the fused six-membered rings of the octahydroquinazoline system and the two spiran cyclohexane rings of (I). The best model was chosen using experimental evidence from 1H and 13C NMR [Contreras et al. (2001). J. Heterocycl. Chem. 38, 1223–1225] in combination with semi-empirical AM1 calculations. In the refined structure the two spiran rings have the chair conformation, while both of the fused rings in the octahydroquinazoline system have half-chair conformations compared with in-vacuum density-functional theory (DFT) B3LYP/6-311G*, DFTB (density-functional tight-binding) theoretical calculations in the solid state and other related structures from X-ray diffraction data. Compound (I) presents weak intramolecular hydrogen bonds of the type N—H...S and C—H...S, which produce delocalization of the electron density in the generated rings described by graph symbols S(6) and S(5). Packing of the molecules is dominated by van der Waals interactions.

Theoreticalversusexperimental geometries in S-bridged manganese carbonyl complexes

2003 ◽  
Vol 36 (4) ◽  
pp. 1050-1055 ◽  
Author(s):  
Juan F. Van der Maelen Uría ◽  
Javier Ruiz ◽  
Santiago García-Granda
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Basis Sets ◽  
Medium Size ◽  
Carbonyl Complexes ◽  
X Ray Diffraction ◽  
Bond Lengths ◽  
Hartree Fock ◽  
Experimental Geometry ◽  
Manganese Carbonyl

The experimental geometry obtained from single-crystal X-ray diffraction for a number of binuclear S-bridged manganese complexes is compared with the results of theoretical calculations made at theab initiolevel by using Hartree–Fock and density functional theory methods with medium-size and large basis sets. The optimized geometries obtained were somewhat relaxed when compared with the experimental ones, with very similar bond and torsion angles but longer bond lengths. The mean square deviation for bond lengths (angles) was found to be between 0.046 Å (1.1°) and 0.004 Å (0.7°) depending on the theoretical model used.

Influence of Fly Ash Fineness on Autoclaved Energy Conservation Block's Performance and Hydration Products

2014 ◽  
Vol 599 ◽  
pp. 302-309 ◽  
Author(s):  
Bao Guo Ma ◽  
Li Xiong Cai ◽  
Shou Wei Jian ◽  
Lei Su
Keyword(s):  
Fly Ash ◽  
Microscopic Analysis ◽  
Production Performance ◽  
Strength Increase ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
Specific Strength ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete

This article discussed the influence of FA fineness on the production performance and usability through the autoclaved aerated concrete slurry gas foaming curve and basic physical properties of blocks; meanwhile, studied the influence of different fineness FA on the composition and morphology of hydration products through X-ray diffraction analysis and scanning electron microscopic analysis, The results show that in the cement-fly ash-lime system autoclaved aerated concrete, the higher fineness of FA, the more water it need, and more sensitive the slurry presents; when the FA residue decrease from 17.8% to 8% through a 0.045mm square hole sieve screen, its specific surface area enlarge from 325m2/Kg to 388m2/Kg, the autoclaved aerated concrete specific strength increase by 53.24% and 40.96% in the case of the same ratio of water and resemble extended degree, respectively. Keep on increasing FA fineness does harm to its specific strength. The crystallinity of tobermorite, which is the main hydration products of autoclaved aerated concrete decreases with the increasing of FA fineness, however, crystallite size become larger.

The first-order structural phase transition of YSb

2010 ◽  
Vol 88 (8) ◽  
pp. 591-596
Author(s):  
Hongzhi Fu ◽  
WenFang Liu ◽  
Tao Gao
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Structural Phase ◽  
Density Functional Theory Method ◽  
Generalized Gradient ◽  
First Order ◽  
Thermal Expansion Coefficients ◽  
Increasing Temperature

The high-pressure induced phase transition of YSb has been studied using the density functional theory method within the generalized gradient approximation. It was found that the first-order structural phase transition began to occur at 30.8 GPa, agreeing well with available experiments and theoretical calculations. In this phase transition, we do not find changes in the heat capacity and thermal expansion coefficients at lower and higher temperature, but the transition pressures decrease with temperature. The bulk modulus and Debye temperature decrease with increasing temperature, while they increase with increasing pressure. Also, the density of states and band structure of these two compounds with B1 and B2 structures have been presented and analyzed.

High Temperature MOVPE Growth of AlxGa1−xN (0.2-1) Layers on Sapphire and SiC Substrates for the Fabrication Deep UV Optical Devices

2006 ◽  
Vol 955 ◽  
Author(s):  
Balakrishnan Krishnan ◽  
Masataka Imura ◽  
Kazuyoshi Iida ◽  
Kentaro Nagamatsu ◽  
Hiroki Sugimura ◽  
...  
Keyword(s):  
High Temperature ◽  
Microscopic Analysis ◽  
Dislocation Loops ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Transmission Electron ◽  
Dislocation Densities ◽  
Transmission Electron Microscopic ◽  
Transmission Electron Microscopic Analysis

ABSTRACTSingle crystalline AlN epitaxial layers have been grown on and (0001) sapphire and 6H-SiC substrates by MOVPE technique at high temperatures in the range of 1340-1500°C. The structural qualities of the high temperature grown AlN layers were found to be good as evidenced by X-ray diffraction analyses results. By transmission electron microscopic analysis, dislocation densities of the layers were found to be 6.2 × 107 cm−2 or lower and the formation of dislocation loops was confirmed. High temperature bridge layers of AlN and AlxGa1−xN layers were grown on linear-groove patterned sapphire based AlN templates and 6H-SiC substrates. AlxGa1−xN bridge layers exhibited different growth behaviours depending on the direction of groove patterns on the sub-strates.

scholarly journals Changes in the structure and properties of ZrO2 detonation coatings during annealing

2020 ◽  
Vol 4 (4) ◽  
pp. 319-326
Author(s):  
B.K. Rakhadilov ◽  
D.N. Kakimzhanov ◽  
G. Botabaeva ◽  
D.B. Buitkenov ◽  
N. Kantai ◽  
...  
Keyword(s):  
Zirconium Dioxide ◽  
Microscopic Analysis ◽  
Thin Layers ◽  
Structure And Properties ◽  
X Ray Diffraction ◽  
Detonation Spraying ◽  
Electron Microscopic ◽  
Before And After ◽  
New Generation ◽  
High Adhesive Strength

The article studied the effect of annealing on the structure and properties of zirconium dioxide coatings obtained by detonation spraying. Detonation spraying was realized on a computerized detonation spraying complex of the new generation CCDS2000. Determined that coatings made of zirconium dioxide are characterized by high adhesive strength of adherence to the substrate. Thermal annealing of coated samples was performed at temperatures of 900-1200◦ C. It was determined that the microhardness of zirconium dioxide coatings increases by 10-25% depending on the annealing temperature after annealing. The results of nanoindentation showed that the nanohardness of the coatings after annealing at 1000◦ C increases by 50%. It was determined that after annealing at 1000◦ C, the elastic modulus of the coatings increases, which indicates a decrease in plasticity and an increase in the strength of the coatings. X-ray diffraction analysis showed that the phase composition of coatings before and after annealing consists of t-ZrO2. After annealing occurs there is an increase in the degree of t-ZrO2 tetragonality. Electron microscopic analysis showed that an increase in the number and size of micro-continuity in the form of thin layers after annealing. Determined that increase the hardness of zirconium dioxide after annealing at 900-1200◦ C is associated with a higher degree of tetragonality t-ZrO2 phase.

scholarly journals Transition Hausmannite Nanoparticles Embedded on Uniform Carbon Micro Spheres Synthesis for Electrochemical Examination

2019 ◽  
Vol 9 (2S2) ◽  
pp. 256-259
Keyword(s):  
Structural Parameters ◽  
Microscopic Analysis ◽  
Spectroscopic Technique ◽  
Maghemite Nanoparticles ◽  
Carbon Spheres ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
Distribution Of Elements ◽  
Scanning Electron Microscopic Analysis ◽  
Charge Discharge

Carbon spheres wrapped by maghemite nanoparticles were synthesized through facile hydrothermal method. The structural parameters were analyzed through powder x-ray diffraction analysis. Functional groups were analyzed by Fourier transform infrared spectroscopic analysis. The prepared carbon spheres wrapped by maghemite nanoparticles morphology were investigated using scanning electron microscopic analysis. The elemental composition and distribution of elements were examined by energy dispersive spectroscopic technique with mapping. Redox property, charge discharge mechanism was done through cyclic voltammetry and galvanostatic charge-discharge studies.

scholarly journals Development of Alginate-Montmorillonite-Starch with Encapsulated Trichoderma harzianum and Evaluation of Conidia Shelf Life

2021 ◽  
Vol 26 (01) ◽  
pp. 87-96
Author(s):  
Fariz Adzmi
Keyword(s):  
Shelf Life ◽  
Trichoderma Harzianum ◽  
Microscopic Analysis ◽  
Threshold Value ◽  
Field Application ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
Scanning Electron Microscopic Analysis ◽  
Encapsulation Method ◽  
The Fourier Transform

Biological control agents, such as Trichoderma harzianum, are widely used in sustainable agriculture. However, commercialisation and mass production of biocontrol products have remained a challenge, especially in viability and efficiency in field application. The encapsulation method has emerged as a sophisticated technique to develop the formulation of T. harzianum. Hence, encapsulation through extrusion was used to prepare T. harzianum beads. The physical characteristics comprising weight, diameter, and swelling ability of the beads were significantly improved when the starch percentage was increased. Alginate-montmorillonite-starch (10%) revealed the lowest shrinkage and the highest swelling ability. The interaction within the functional groups of alginate, montmorillonite, and starch was confirmed by the Fourier-transform infrared spectroscopic (FTIR) study. Furthermore, scanning electron microscopic analysis exposed compatible scattering of montmorillonite particles and starch granules over the alginate linkages. Meanwhile, the X-ray diffraction analysis confirmed the exfoliation between starch and montmorillonite. Storage of T. harzianum beads at 5°C was more suitable than storage at 28°C. At low temperature, the encapsulated T. harzianum beads maintained their viability at 6.59 ± 0.12 log CFU g−1 for an effective threshold value for up to seven months. The current findings indicated that the combination of alginate, montmorillonite, and starch is the best formulation of encapsulated T. harzianum with improved conidia shelf life. © 2021 Friends Science Publishers

scholarly journals SIMULASI PERUBAHAN DENSITAS MUATAN ADSORPSI ATOM HIDROGEN-GRAFENA DENGAN TEORI FUNGSI KERAPATAN

2018 ◽  
Vol 3 (2) ◽  
pp. 179-184
Author(s):  
Albert Zicko Johannes
Keyword(s):  
Density Functional Theory ◽  
Hydrogen Atom ◽  
Charge Density ◽  
Density Functional ◽  
Structural Changes ◽  
Density Functional Theory Method ◽  
Hexagonal Structure ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Center Position

Abstrak Peristiwa adsorpsi atom Hidrogen pada Grafena menyebabkan terjadinya perubahan struktur Grafena. Perubahan ini mempengaruhi keadaan densitas muatan Grafena. Pada simulasi ini posisi atom Hidrogen pada permukaan lembaran Grafena divariasikan, yaitu pada posisi tepat di atas atom Karbon (Top), posisi di tengah antara dua atom Karbon (Bridge), dan posisi pusat struktur heksagonal (Hollow). Simulasi dilakukan dengan metode Teori Fungsi Kerapatan dengan model Grafena ukuran 2x2. Hasil yang diperoleh menunjukkan adsorpsi atom Hidrogen memilih posisi Top sebagai yang paling stabil dibandingkan dengan posisi Bridge dan Hollow. Hasil dari posisi Top menunjukkan elektron dari atom Hidrogen digunakan mengikat Grafena dengan energi ikat sebesar -1.7 eV. Perubahan densitas muatan menunjukkan terjadinya perpindahan elektron menuju Grafena disertai transformasi isosurface yang unik untuk setiap posisi atom Hidrogen dengan perubahan terbesar terjadi pada posisi Top.  Kata kunci: Densitas muatan, Grafena, Adsorpsi, Teori Fungsi Kerapatan  Abstract [Title: The Simulation of Charge Density Diffrential for Hydrogen Atom - Graphene Adsorption with Density Functional Theory] Hydrogen atom adsorption on Graphene cause structural changes. This change affect Graphene charge density. In this simulation the position of Hydrogen atom on the surface of Graphene sheet are varied out, which is on the position directly above the Carbon atom (Top), the position on the middle between two Carbon atoms (Bridge), and the center position of the hexagonal structure (Hollow). The simulation is done by the Density Functional Theory method with a 2x2 size Graphene model. The results obtained showed that Hydrogen atom adsorption chose the Top position as the most balanced compared with the position of Bridge and Hollow. The results from the Top position indicate that electrons from Hydrogen atom are used to bind the Graphene with binding energy of -1.7 eV. The charge density differential indicate the occurrence of electron transfer towards Graphene accompanied by a transformation of the isosurface that are unique for each Hydrogen atom positions with the biggest change is shown in the Top position.  Keywords: Charge Density, Graphene, Adsorption, Density Functional Theory

scholarly journals Effective Temperature of ZnO Nanoparticles

2020 ◽  
pp. 213-218
Author(s):  
San San Htwe ◽  
Sanda Win ◽  
Myint Myint Swe ◽  
Sandar Win
Keyword(s):  
Modern Science ◽  
Microscopic Analysis ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
Zno Nps ◽  
Electron Microscopic ◽  
Scanning Electron Microscopic ◽  
Different Temperatures ◽  
Scanning Electron Microscopic Analysis ◽  
Uv Visible

In modern science Nanotechnology is the field for the researchers. Nanoparticles have a size of 1-100 nm with a surrounding interfacial layer. Many researchers characterize significantly concerning medical chemistry, atomic physics, and all other known fields. Zinc oxide nanoparticles were synthesized with precipitation method after annealing the precursor at different temperatures. The effects of annealing temperatures for the precursors on the particle size of ZnO NPs were investigated. The structure and composition of the precursor and prepared ZnO NPs will study using X-ray diffraction (XRD), Scanning Electron Microscopic Analysis (SEM), and the optical properties of the ZnO NPs will characterize using UV-visible spectroscopy.

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