Suppression of the spiral‐growth mechanism in epitaxial YBa2Cu3O7−xfilms grown on miscut substrates

1992 ◽  
Vol 61 (7) ◽  
pp. 852-854 ◽  
Author(s):  
Douglas H. Lowndes ◽  
X.‐Y. Zheng ◽  
Shen Zhu ◽  
J. D. Budai ◽  
R. J. Warmack
Keyword(s):  
Growth Mechanism ◽  
Spiral Growth

Experimental and theoretical studies of the mica polymorphs

1956 ◽  
Vol 31 (234) ◽  
pp. 209-235 ◽  
Author(s):  
J. V. Smith ◽  
H. S. Yoder
Keyword(s):  
Growth Mechanism ◽  
Theoretical Study ◽  
Dominant Role ◽  
Spiral Growth ◽  
Theoretical Studies ◽  
X Ray ◽  
Layer Cell ◽  
Triclinic Structure ◽  
Experimental And Theoretical Studies ◽  
Made In

SummaryAn experimental and theoretical study has been made in order to determine the number and the structure of the possible polymorphs and to determine the structural relations between them. The simplest structures are 1M, 2M1, 2M2, 3T, 20, and 6H polymorphs, and more complicated types can be developed. Some of the previously described polymorphs were not contained in the theoretical list and were re-examined. The 6M structure was found to be a 2M2 polymorph, the 6-layer triclinic type was found to be a 2M1 polymorph, and the 3M structure was shown to be a 3T type. The 24-layer triclinic structure could be described on a simpler 8-layer cell. This type together with a new 12-layer monoclinic structure, as well as other structures of higher periodicity, presumably consists of complex stacking and results from spiral-growth mechanism. Two extreme types of layer-disordered crystals may be built and a disorder of individual ions may also occur. Single stacking faults result in twinned crystals. A new twin relation (180° rotation about the [100] axis) has been recognized. Twenty specimens from extreme geological environments have been examined in order to evaluate the control of environment on the stacking. The type of stacking could not be attributed solely to the influence of pressure and temperature. Composition appears to play a dominant role in the type of stacking, and semi-quantitative structural arguments appear to support this contention. The influence of growth mechanism is discussed. A scheme for the identification of the mica polymorphs by X-ray powder and single-crystal methods is given.

Graphite Morphology Control in Cast Iron

1984 ◽  
Vol 34 ◽  
Author(s):  
S. V. Subramanian ◽  
D. A. R. Kay ◽  
G. R. Purdy
Keyword(s):  
Cast Iron ◽  
Growth Mechanism ◽  
Driving Forces ◽  
Morphology Control ◽  
Spiral Growth ◽  
Compacted Graphite ◽  
Spherulitic Morphology ◽  
Graphite Morphology ◽  
Control Diagram ◽  
Graphite Growth

ABSTRACTGraphite morphology in cast iron is analyzed in terms of the growth kinetics of graphite crystals in liquid iron. At small driving forces, i.e., low supersaturation or small kinetic undercooling, graphite growth is characterized by faceted growth, resulting in flake, compacted and spherulitic graphite morphologies. However, at large driving forces, there is a transition from facted to non-faceted growth, resulting in a dendritic growth morphology.Flake morphology is rationalized in terms of impurity dependent crystal growth mechanisms, whereas a spherulitic morphology is attributed to a defect controlled spiral growth mechanism. Compacted graphite morphology is considered as a transition between flake and spherulitic morphology.A thermodynamic approach is used to inter-relate the residual concentrations of impurities of technological interest, i.e. S and 0, as a function of the residual concentration of the reactive elements, Mg, Ca, and Ce in a typical cast iron melt at 1500'C and atmospheric pressure. Such a diagram that quantitatively relates graphite morphology in thick cast iron sections to soluble concentrations of impurities is referred to as a graphite morphology control diagram.In thin section castings that freeze at faster cooling rates and large kinetic undercoolings, the basal spiral growth mechanism dominates over the impurity controlled prism growth mechanism, leading to deviations from predictions based simply on the graphite morphology control diagram. In the ase of compacted graphite, where growth on both the prism and basal faces is involved, the degree of nodularity increases with the cooling rate, giving rise to section sensitivity.At large undercoolings, the prevention of the nucleation and growth of cementite is an essential feature of graphite morphology control. It is estimated that the mobility of the cementite interface exceeds that of the prism interface in flake graphite growth by an order of magnitude and that of the basal interface in spherulitic graphite growth by three orders of magnitude. In practice, the driving force for graphite growth is raised selectively through the addition of graphite stabilizing elements, such as silicon, which raise the temperature of the graphite eutectic and depress the temperature of the carbide eutectic. Kinetic growth undercooling can be decreased by increasing the number of heterogeneous nuclei for graphite growth through inoculation. The application of the above concepts for the control of graphite morphology in shaped automotive castings is discussed.

Epitaxial YBa2Cu3O7−x Thin Films: Scanning Tunneling Microscope Study of the Initial Stages of Epitaxial Growth, Growth Mechanism, and Effects of Substrate Temperature

1991 ◽  
Vol 237 ◽  
Author(s):  
Shen Zhu ◽  
Douglas H. Lowndes ◽  
X.-Y. Zheng ◽  
David P. Norton ◽  
R. J. Warmack
Keyword(s):  
Film Thickness ◽  
Growth Mechanism ◽  
Growth Temperature ◽  
Lattice Mismatch ◽  
Unit Cell ◽  
Growth Mode ◽  
Spiral Growth ◽  
Scanning Tunneling ◽  
Growth Stages ◽  
Island Growth

ABSTRACTThe surface microstructure of epitaxial YBa2Cu3O7−x films grown by pulsed laser ablation on (001) MgO and SrTiO3 substrates has been studied at various growth stages, ranging in thickness from eight c-axis perpendicular unit cells to ∼220 nm. On MgO (lattice mismatch ∼9%) even the thinnest films grow unit cell-by-unit cell by an island growth mechanism. However, on SrTi03 (mismatch ∼1%), a transition from a layer-like growth mode to island growth is observed as the film thickness increases. Islands with clear spiral growth structures are observed in even the thinnest films on MgO, but for films grown on SrTiO3 the spiral growth features are found only for film thicknesses slightly greater than the critical thickness for the switch to an island growth mode. The islands consist of stacks of atomically flat terraces whose step heights are multiples of the c-axis lattice parameter. The island density decreases significantly with increasing film thickness, while their diameters range from 50–400 nm, increasing with growth temperature. The terraced island grain morphology causes a surface roughness of from 10 to 30 nm (depending on growth temperature) in films ∼200 nm thick.

ANALYSIS OF GROWTH MECHANISM OF DENDRITIC TITANIUM CARBIDES PRODUCED BY LASER ALLOYING OF PURE TITANIUM WITH GRAPHITE POWDER

2005 ◽  
Vol 12 (01) ◽  
pp. 41-45 ◽  
Author(s):  
Y. S. TIAN ◽  
C. Z. CHEN ◽  
D. Y. WANG ◽  
Q. H. HUO ◽  
T. Q. LEI
Keyword(s):  
Growth Mechanism ◽  
Pure Titanium ◽  
Graphite Powder ◽  
Spiral Growth ◽  
Crystal Surfaces ◽  
Linear Arrangement ◽  
Continuous Growth ◽  
Electron Probe Microanalyzer ◽  
Transmission Electron ◽  
Titanium Carbides

The microstructure of dendritic titanium carbides fabricated by laser surface alloying of pure titanium with graphite powder is investigated using electron probe microanalyzer (EPMA) and high-resolution transmission electron microscope (HRTEM). The growth mechanism of TiC crystals is that crystal grows by the model of continuous growth at the beginning of solidification and then the crystal surfaces that are suited to lateral growth develop fully by the model of spiral growth. So, the final morphology of dendritic TiC looks like it is composed of tiny crystal grains in a linear arrangement.

The study of crystal growth with the electron microscope II. The observation of growth steps in the paraffin n -hectane

1952 ◽  
Vol 214 (1116) ◽  
pp. 72-79 ◽  
Keyword(s):  
Electron Microscope ◽  
Crystal Growth ◽  
Twin Boundary ◽  
Growth Mechanism ◽  
The Other ◽  
Spiral Growth ◽  
Growth Mechanisms ◽  
Slow Evaporation ◽  
Orthorhombic Cell ◽  
The One

Examination of the paraffin n -hectane in the electron microscope has given evidence of two different growth mechanisms for crystals of this compound. The one corresponds to the spiral growth mechanism already observed for n -hexatriacontane (Dawson & Vand 1951), and the orthorhombic lozenge-shaped crystals of n -hectane show the typical spiral growth steps already described. The other growth mechanism gives rise to lath-shaped crystals and operates when growth takes place by the slow evaporation of a cold solution of n -hectane in xylene. The laths are invariably twinned across the diagonal of the orthorhombic cell, and growth in one direction is greatly accelerated by the occurrence of an indestructible step at the twin boundary.

Controlled growth of MoS2 nanopetals and their hydrogen evolution performance

RSC Advances ◽  
2016 ◽  
Vol 6 (22) ◽  
pp. 18483-18489 ◽  
Author(s):  
Lin Ling ◽  
Chan Wang ◽  
Kai Zhang ◽  
Taotao Li ◽  
Lei Tang ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Growth Mechanism ◽  
Spiral Growth ◽  
Controlled Growth ◽  
Vertical Growth

From horizontal to vertical growth, dense edge-oriented MoS2 nanopetals have been synthesized via an APCVD method through the spiral growth mechanism.

Copper Pentagonal Micropyramids Grown by Mechanically Activated Electrodeposition

2018 ◽  
Vol 55 (1) ◽  
pp. 78-81
Author(s):  
A.A. Vikarchuk ◽  
N.N. Gryzunova ◽  
M.Yu. Gutkin ◽  
A.E. Romanov
Keyword(s):  
Mechanical Activation ◽  
Growth Mechanism ◽  
Layer Growth ◽  
Crystallographic Plane ◽  
Spiral Growth ◽  
Twin Boundaries ◽  
Growth Step ◽  
Metal Atoms

Abstract The formation of copper pentagonal micropyramids (PMPs) with high (multiatomic) spiral growth steps, which are grown by electrocrystallization with mechanical activation of the cathode, is studied experimentally. A new spiral-layer growth mechanism for the formation of such PMP is proposed. It is shown that PMPs grow on flat pentagonal microcrystals (PMCs) formed initially and containing fivefold twins with one of the twin boundaries being inclined by the angle of 35°16’ to the {110}-type substrate crystallographic plane. Such crystal geometry causes an inclined growth step on the PMC surface. The preferential deposition of metal atoms on this step leads to the spiral-layer PMC growth and the formation of PMPs with a structure inherited from the PMCs.

scholarly journals MECHANISM OF BORAX CRYSTALLIZATION USING CONDUCTIVITY METHOD

2010 ◽  
Vol 8 (3) ◽  
pp. 327-330
Author(s):  
Suharso Suharso
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Growth Mechanism ◽  
Spiral Growth ◽  
High Concentration ◽  
Conductivity Method ◽  
Principal Mechanism ◽  
Low Concentration ◽  
Kinetics Of ◽  
Kinetics Of Crystal Growth

The kinetics of crystal growth of borax has been studied by using conductivity method at temperature of 25 °C and at various relative supersaturations. It was found that the growth rate increases with increasing supersaturation. At low concentration, growth occurs via a spiral growth mechanism and at high concentration birth and spread is the principal mechanism operating.     Keywords: borax; growth rate; crystallization; conductivity method

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