Growth mechanism of YBa2Cu3O7-x by reactive coevaporation and superconductivity of the one-unit-cell layer

1994 ◽  
pp. 499-504
Author(s):  
Yoshichika Bando ◽  
Takahito Terashima ◽  
Kenichi Shimura ◽  
Yoshihiro Daitoh ◽  
Yuji Matsuda ◽  
...  
Keyword(s):  
Growth Mechanism ◽  
Cell Layer ◽  
Unit Cell ◽  
The One

Structure Information From Electron Diffraction Intensities

1990 ◽  
Vol 48 (2) ◽  
pp. 516-517
Author(s):  
J. Gjønnes ◽  
N. Bøe ◽  
K. Gjønnes
Keyword(s):  
Computational Effort ◽  
Unit Cell ◽  
Small Unit ◽  
Structure Information ◽  
Dispersion Surface ◽  
Integrated Intensity ◽  
The One ◽  
Image Position ◽  
Convergent Beam ◽  
Beam Patterns

Structure information of high precision can be extracted from intentsity details in convergent beam patterns like the one reproduced in Fig 1. From low order reflections for small unit cell crystals,bonding charges, ionicities and atomic parameters can be derived, (Zuo, Spence and O’Keefe, 1988; Zuo, Spence and Høier 1989; Gjønnes, Matsuhata and Taftø, 1989) , but extension to larger unit cell ma seem difficult. The disks must then be reduced in order to avoid overlap calculations will become more complex and intensity features often less distinct Several avenues may be then explored: increased computational effort in order to handle the necessary many-parameter dynamical calculations; use of zone axis intensities at symmetry positions within the CBED disks, as in Figure 2 measurement of integrated intensity across K-line segments. In the last case measurable quantities which are well defined also from a theoretical viewpoint can be related to a two-beam like expression for the intensity profile:With as an effective Fourier potential equated to a gap at the dispersion surface, this intensity can be integrated across the line, with kinematical and dynamical limits proportional to and at low and high thickness respctively (Blackman, 1939).

scholarly journals In-situ HRTEM observations of growth process of decagonal quasicrystals

2014 ◽  
Vol 70 (a1) ◽  
pp. C97-C97
Author(s):  
Keisuke Nagao ◽  
Kazue Nishimoto ◽  
Tomoaki Inuduka ◽  
Keiichi Edagawa
Keyword(s):  
Growth Mechanism ◽  
Growth Process ◽  
Structural Information ◽  
Growth Models ◽  
Experimental Studies ◽  
Unit Cell ◽  
Small Scale ◽  
Growth Processes ◽  
Decagonal Quasicrystals

Quasicrystals possess quasiperiodicity, where the structure cannot be described simply by the repetition of unit cell like conventional crystals. This fact raises the question of how quasicrystals grow, i.e., what physical mechanism makes the growth of quasicrystals possible. While crystals can grow by copying a unit cell via local atomic interactions, nonlocal structural information seems to be required in the growth of quasicrystals. This problem has attracted much attention ever since the first discovery of a quasicrystal in 1984, and several theoretical growth models [1] have been proposed. However, no experimental studies have so far been reported, and it is still unclear whether these theoretical growth models apply to real quasicrystals. In the present study, we have conducted in-situ high-temperature electron microscopic (HRTEM: High-Resolution Transmission Electron Microscopy) observations of the growth process of decagonal quasicrystals to elucidate the growth mechanism. The growth processes of a decagonal quasicrystal of Al70.8Ni19.7Co9.5were observed by HRTEM in the temperature range 1073-1173K. Tiling patterns with edge length of about 2nm were constructed from a series of HRTEM images. They were analysed in the framework of the projection method. Here, we followed the procedures in our previous work [2]. We have already reported the results of some observations and analyses elsewhere [3]. However, the growth processes of them were on a small scale, and the results were indefinite. Recently, we have succeeded in observing a growth process on a massive scale. In this paper, we present the results of this observation and subsequent analyses, and discuss the growth mechanism of the quasicrystal.

Atomic Layer and Unit-Cell Layer Growth of (Ca,Sr)CuO2 and Bi2Sr2Can-1CunO2n+4 Thin Films by Laser Molecular Bean Epitaxy

1991 ◽  
Vol 222 ◽  
Author(s):  
Masaki Kanai ◽  
Tomoji Kawai ◽  
Takuya Matsumoto ◽  
Shichio Kawai
Keyword(s):  
Thin Films ◽  
Diffraction Pattern ◽  
Cell Layer ◽  
Atomic Layer ◽  
High Energy ◽  
Layer Growth ◽  
Unit Cell ◽  
Layer By Layer ◽  
Diffraction Intensity

ABSTRACTThin films of (Ca,Sr)CuO2 and Bi2Sr2Can-1CunO2n+4 are formed by laser molecular beam epitaxy with in-situ reflection high energy electron diffraction observation. The diffraction pattern shows that these materials are formed with layer-by-layer growth. The change of the diffraction intensity as well as the analysis of the total diffraction pattern makes It possible to control the grown of the atomic layer or the unit-cell layer.

Unit cell layer-by-layer heteroepitaxy of BaO thin films at temperatures as low as 20 °C

1997 ◽  
Vol 15 (5) ◽  
pp. 2469-2472 ◽  
Author(s):  
T. Ohnishi ◽  
M. Yoshimoto ◽  
G. H. Lee ◽  
T. Maeda ◽  
H. Koinuma
Keyword(s):  
Thin Films ◽  
Cell Layer ◽  
Unit Cell ◽  
Layer By Layer

Origin of Giant Seebeck Coefficient for High Density 2DEGs Confined in the SrTiO3/SrTi0.8Nb0.2O3 Superlattices

2007 ◽  
Vol 1044 ◽  
Author(s):  
Yoriko Mune ◽  
Hiromichi Ohta ◽  
Teruyasu Mizoguchi ◽  
Yuichi Ikuhara ◽  
Kunihito Koumoto
Keyword(s):  
Seebeck Coefficient ◽  
Electron Tunneling ◽  
Cell Layer ◽  
Unit Cell ◽  
High Density ◽  
Practical Application ◽  
Dimensional Electron ◽  
Quantum Size ◽  
Cell Layers ◽  
Dimensional Electron Gas

AbstractRecently, we have found that high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 exhibits extremely large Seebeck coefficient (|S|2D) [REF], approximately five times larger than |S|3D. Here we clarify the origin of giant |S|2D using [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]20 (x = 1∼60, y = 1∼20) superlattices. The |S|2D value increased proportionally to y{0.5, indicating that the density of states of the conduction band increases with decreasing y (quantum size effect). Superlattices of [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z (x = 0∼60, y = 1∼20, z = 20) were fabricated on the (001)-face of LaAlO3 substrate by PLD using RHEED to count the number of SrTiO3 or SrTi0.8Nb0.2O3 layers. HR-XRD and HAADF-STEM studies revealed that high-quality [(SrTiO3)17/(SrTi0.8Nb0.2O3)y]z superlattices were successfully fabricated. A dramatic increase of |S|2D is seen with decreasing y-value of the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices. The slope for the plots of log |S|2D - log y is -0.5, and reached 290 μVK−1 (y = 1), which is ∼5 times larger than that of the SrTi0.8Nb0.2O3 bulk (|S|3D = 61 μVK−1). Further, the |S|2D value monotonically increases with x-value and is saturated when x-value > 16 (6.25 nm). We clarified that the critical barrier thickness for electron tunneling in [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattice is 6.25 nm (16 unit cell layers of SrTiO3). The present results give very important information to utilize the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices for practical application.

Indexing Powder Patterns from Relative Axial Dimensions

1990 ◽  
Vol 5 (2) ◽  
pp. 61-63
Author(s):  
Ben Post ◽  
W. Frank McClune
Keyword(s):  
Data Base ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Single Phase ◽  
Unit Cell ◽  
X Ray ◽  
Large Numbers ◽  
Diffraction Patterns ◽  
Goniometric Measurements ◽  
The One

The usefulness of an X-ray powder diffraction data base, such as the one published by the International Centre for Diffraction Data, is largely dependent on continued additions of indexed powder patterns of single-phase materials of interest to data-base users. The single-phase character of a specimen is generally established by using known values of the unit cell constants to index all its powder pattern lines.In this manuscript we describe indexing procedures based on crystal data which provide only relative values of the cell dimensions, rather than the absolute values usually considered to be essential to the indexing process. To the best of our knowledge, the use of such data for indexing powder diffraction patterns has generally been overlooked or ignored by X-ray crystallographers. We refer to the large numbers of goniometric measurements of crystals which have been published both before, and since, the discovery of X-ray diffraction. These provide useful descriptions of chemical and physical properties of crystals as well as measurements of relative dimensions of unit cell axes. The latter are presented in the form of a/b, b/b and c/b, together with the interaxial angle or angles, if the cell is nonorthogonal.

Mechanism of the Acicular Nanosize Mg,Al-Hydrotalcite Grain Growth under Hydrothermal Conditions

2007 ◽  
Vol 280-283 ◽  
pp. 489-494
Author(s):  
Qing Li Ren ◽  
Qiang Luo ◽  
Wei Chen
Keyword(s):  
Growth Mechanism ◽  
Atmospheric Pressure ◽  
Growth Unit ◽  
Growth Theory ◽  
Test Results ◽  
Hydrothermal Conditions ◽  
Reaction Method ◽  
Liquid Reaction ◽  
One Step ◽  
The One

The highly pure acicular nanosize Mg,Al-hydrotalcite was synthesized by the one-step liquid reaction method at atmospheric pressure. The favorable growth unit in the reaction liquid, the requirements of Al3+ entering the Mg2+-(OH-)6 octahedral and forming the growth unit M-(OH-1)6 (M=Mg2+, Al3+) and growth mechanism that the nanosize Mg,Al-hydrotalcite crystal embryo follows are studied according to the test results of XRD, TEM, SEM and IR. Later, that the nanosize Mg,Alhydrotalcite crystal embryo growth follows the gathering growth theory was deeply investigated.

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