scholarly journals Defects of diamond crystal structure as an indicator of crystallogenesis

2021 ◽  
Vol 250 ◽  
pp. 481-491
Author(s):  
Evgeny Vasilev
Keyword(s):  
Crystal Structure ◽  
Growth Mechanism ◽  
Normal Growth ◽  
Morphological Diversity ◽  
Population Diversity ◽  
Crystal Habit ◽  
Impurity Composition ◽  
Structure Defects ◽  
Intermediate Chamber ◽  
Geological Formations

Based on the study of a representative collections of diamonds from diamondiferous formations of the Urals and deposits of the Arkhangelsk and Yakutian diamond provinces, we established patterns of zonal and sectoral distribution of crystal structure defects in crystals of different morphological types, identified the specifics of crystals formed at different stages of crystallogenesis and performed a comprehensive analysis of constitutional and population diversity of diamonds in different formations. We identified three stages in the crystallogenesis cycle, which correspond to normal and tangential mechanisms of growth and the stage of changing crystal habit shape. At the stage of changing crystal habit shape, insufficient carbon supersaturation obstructs normal growth mechanism, and the facets develop from existing surfaces. Due to the absent stage of growth layer nucleation, formation of new {111} surfaces occurs much faster compared to tangential growth mechanism. This effect allows to explain the absence of cuboids with highly transformed nitrogen defects at the A-B1 stage: they have all been refaceted by a regenerative mechanism. Based on the revealed patterns, a model of diamond crystallogenesis was developed, which takes into account the regularities of growth evolution, thermal history and morphological diversity of the crystals. The model implies the possibility of a multiply repetitive crystallization cycle and the existence of an intermediate chamber; it allows to explain the sequence of changes in morphology and defect-impurity composition of crystals, as well as a combination of constitutional and population diversity of diamonds from different geological formations.

High resolution STEM imaging study on high Tc superconductor YBa2CuaO7-x

1988 ◽  
Vol 46 ◽  
pp. 882-883
Author(s):  
H.-J. Ou ◽  
J. M. Cowley
Keyword(s):  
Crystal Structure ◽  
High Resolution ◽  
Grain Boundary ◽  
Strong Field ◽  
Imaging Study ◽  
Structure Defects ◽  
High Tc ◽  
High Tc Superconductor ◽  
Diffraction Patterns ◽  
Lattice Planes

Using the dedicate VG-HB5 STEM microscope, the crystal structure of high Tc superconductor of YBa2Cu3O7-x has been studied via high resolution STEM (HRSTEM) imaging and nanobeam (∽3A) diffraction patterns. Figure 1(a) and 2(a) illustrate the HRSTEM image taken at 10' times magnification along [001] direction and [100] direction, respectively. In figure 1(a), a grain boundary with strong field contrast is seen between two crystal regions A and B. The grain boundary appears to be parallel to a (110) plane, although it is not possible to determine [100] and [001] axes as it is in other regions which contain twin planes [3]. Following the horizontal lattice lines, from left to right across the grain boundary, a lattice bending of ∽4° is noticed. Three extra lattice planes, indicated by arrows, were found to terminate at the grain boundary and form dislocations. It is believed that due to different chemical composition, such structure defects occur during crystal growth. No bending is observed along the vertical lattice lines.

Calcite crystallization in the cement system: morphological diversity, growth mechanism and shape evolution

2018 ◽  
Vol 20 (20) ◽  
pp. 14174-14181 ◽  
Author(s):  
Jinyang Jiang ◽  
Qi Zheng ◽  
Dongshuai Hou ◽  
Yiru Yan ◽  
Heng Chen ◽  
...  
Keyword(s):  
Growth Mechanism ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Morphological Diversity ◽  
Low Ph ◽  
Shape Evolution ◽  
Engineering Construction ◽  
Cement System

Carbonation plays an indispensable role in engineering construction, embracing mineralization, CO2 sequestration and low pH induced corrosion, but the essential mechanism of carbonation occurring in calcium silicate hydrate or portlandite can hardly be interpreted.

NUMERICAL MODELING OF RADIATION EXPOSURE ON A QUARTZ CRYSTAL STRUCTURE DEFECTS AND SIGNAL ANALYSIS THERMOLUMINESCENT

2020 ◽  
Vol 6 (4) ◽  
pp. 158-178
Author(s):  
Vladimir S. Sheinkman ◽  
Yuliya Yu. Erina ◽  
Oleg A. Simonov
Keyword(s):  
Crystal Structure ◽  
Radiation Exposure ◽  
Electron Concentration ◽  
Numerical Experiments ◽  
Quartz Crystal ◽  
Equilibrium Concentration ◽  
Band Model ◽  
Structure Defects ◽  
Crystal Structure Defects ◽  
Intense Radiation

Developing thermoluminescent (TL) dating methods for quartz-containing deposits has required a series of numerical experiments within the framework of the band model to study the rate of electron accumulation in quartz crystal structure defects under radioactive radiation. The crystal model contained two different types of electron traps and one emission center. A system of differential equations was solved numerically, relating the rates of change in the electron concentration in defects of the crystal structure and the electron concentration in the conduction band and holes in the valence band. The results have shown that the intense radiation exposure alters the dynamic equilibrium concentration of electrons in the traps, which significantly modifies the TL signal. In accordance with this, the sensitivity marker material to the radioactive dose, required for absolute dating and received by its intense radiation exposure, cannot be determined correctly. In addition, the numerical experiments have confirmed the possibility of dating the samples by the position of the TL signal’s maximum on the time axis, as well as the possibility of obtaining the dating by the TL signal’s amplitude.

scholarly journals Texture and Stress Evolution in HfN Films Sputter-Deposited at Oblique Angles

Coatings ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 712 ◽  
Author(s):  
Grégory Abadias ◽  
Fırat Anğay ◽  
Rubenson Mareus ◽  
Cédric Mastail
Keyword(s):  
Crystal Structure ◽  
Residual Stress ◽  
Tilt Angle ◽  
Particle Flux ◽  
Substrate Surface ◽  
Crystal Habit ◽  
Average Kinetic Energy ◽  
Oblique Angle Deposition ◽  
Stress Evolution ◽  
Stress Changes

In this study, polycrystalline hafnium nitride (HfN) thin films were grown by oblique angle deposition (OAD) technique to investigate the relationship between column tilt angle, texture development and residual stress evolution with varying inclination angle α of the substrate. The films (~1 μm thickness) were grown at various angles (α = 5°, 25°, 35°, 65°, 75°, and 85°) with respect to the substrate normal by reactive magnetron sputtering at 0.3 Pa and 300 °C. The film morphology, crystal structure and residual stress state were characterized by scanning electron microscopy and X-ray diffraction (XRD), including pole figure and sin2ψ measurements. All HfN films had a cubic, NaCl-type crystal structure with an [111] out-of-plane orientation and exhibited a biaxial texture for α ≥ 35°. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids, with a side and a corner facing the projection of the incoming particle flux (indicative of a double in-plane alignment). A columnar microstructure was formed for α ≥ 35°, with typical column widths of 100 nm. It is observed that the column tilt angle β increases monotonously for α ≥ 35°, reaching β = 34° at α = 85°. This variation at microscopic scale is correlated with the tilt angle of the (111) crystallographic planes, changing from −24.8 to 11.3° with respect to the substrate surface. The residual stress changes from strongly compressive (~−5 GPa at α = 5°) to negligible or slightly tensile for α ≥ 35°. The observed trends are compared to previous works of the literature and discussed based on existing crystal growth and stress models, as well as in light of energy and angular distribution of the incident particle flux calculated by Monte Carlo. Importantly, a decrease of the average kinetic energy of Hf particles from 22.4 to 17.7 eV is found with increasing α due to an increase number of collisions.

Growth mechanism and crystal habit of RBa2Cu3O7-x (R = Y, Tm, Gd) single crystals

1993 ◽  
Vol 129 (3-4) ◽  
pp. 411-415 ◽  
Author(s):  
S.X. Shang ◽  
H. Wang ◽  
X.L. Sheng
Keyword(s):  
Single Crystals ◽  
Growth Mechanism ◽  
Crystal Habit

Some examples of polyoxometalates crystal structure defects

2011 ◽  
Vol 67 (a1) ◽  
pp. C807-C807
Author(s):  
G. Leitus ◽  
L. J. W. Shimon ◽  
Y. Diskin-Posner ◽  
A. M. Khenkin ◽  
R. Neumann
Keyword(s):  
Crystal Structure ◽  
Structure Defects ◽  
Crystal Structure Defects

scholarly journals Hydrogen bonding structure and polymorphism in agrochemicals

2014 ◽  
Vol 70 (a1) ◽  
pp. C540-C540
Author(s):  
Antonietta Di Pumpo ◽  
Mark Weller ◽  
Sax Mason ◽  
Marie-Hélène Lemée-Cailleau
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Hydrogen Atom ◽  
Hydrogen Bonds ◽  
Physical Properties ◽  
Crystallization Process ◽  
Spatial Arrangement ◽  
Crystal Habit ◽  
Bonding Structure ◽  
Significant Toxicity

Polymorphism of crystals, crystal habit and crystal growth are important factors that must be controlled for any commercial crystallization process. Pharmaceuticals and agrochemicals are two of the most industrially-important, active-molecule systems for which the physical properties are strongly correlated to their crystal structure. While pharmaceuticals have attracted more academic interest to date, the market for agrochemicals is also very considerable, amounting to $15 bn annually. Given the potential significant toxicity of some agrochemicals, the ability to control physical properties such as solubility and dissolution rates, which depend on the crystal structure of the agrochemical itself, represents a way of optimizing the ratio between the amount of product used and its efficiency, improving its function and reducing its environmental impact. Hydrogen bonds play a crucial role in the spatial arrangement of the active molecules and the crystallization process. However, high accuracy and precision of the hydrogen atom positions can only be achieved through single crystal neutron diffraction (SND). SND experiments have been performed on three herbicides - isoproturon (IPU), pendimethalin (PDM), and diflufenican (DFF) - and the fungicide cyprodinil (CYP) [1][2]. All four structure refinements show a ten-time improvement in precision in the hydrogen atom positions compared to SXD with accurately determined nuclear positions. For cyprodinil, which crystallises as two polymorphs, A and B, differences in the hydrogen bonding network have been determined. Form A is governed by single, linear hydrogen bonds between two molecules, while the B form is characterized by the presence of dimers linked through pairs of hydrogen bonds, leading to a stable 8-membered ring. These differences in structure are reflected in the physical properties of the two polymorphs such as melting point and the observed slow inter-conversion that takes place during storage.

scholarly journals New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies

2016 ◽  
Vol 191 ◽  
pp. 511-525 ◽  
Author(s):  
Guillaume Gouget ◽  
Patricia Beaunier ◽  
David Portehault ◽  
Clément Sanchez
Keyword(s):  
Crystal Structure ◽  
Case Studies ◽  
Molten Salts ◽  
Nanoparticle Synthesis ◽  
Crystal Habit ◽  
Metal Boride ◽  
Crystalline Phases ◽  
Metal Borides ◽  
Crystalline Metal ◽  
First Time

Herein we highlight for the first time the ability to tune the stoichiometry of metal boride nanocrystals through nanoparticle synthesis in thermally stable inorganic molten salts. Two metal–boron systems are chosen as case studies: boron-poor nickel borides and boron-rich yttrium borides. We show that NiB, Ni4B3, Ni2B, Ni3B, and YB6 particles can be obtained as crystalline phases with good selectivity. Anisotropic crystallization is observed in two cases: the first boron-rich YB4 nanorods are reported, while boron-poor NiB nanoparticles show a peculiar crystal habit, as they are obtained as spheres with uniaxial defects related to the crystal structure. Crystallization mechanisms are proposed to account for the appearance of these two kinds of anisotropy at the nanoscale.

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