Epitaxial Variants and Grain Boundary Structures in Heteroepitaxial Lithium Tantalate on Basal Sapphire

1996 ◽  
Vol 441 ◽  
Author(s):  
Robert A. Bellman ◽  
Rishi Raj
Keyword(s):  
Grain Boundary ◽  
Stoichiometric Composition ◽  
Lithium Tantalate ◽  
Grain Structure ◽  
Chemical Beam Epitaxy ◽  
Heteroepitaxial Growth ◽  
Crystalline Perfection ◽  
Electro Optic ◽  
Optical Applications ◽  
High Degree

AbstractSingle crystal heteroepitaxial ferroelectric films are desired for non-linear optical applications to maximize the electro-optic coefficient and minimize waveguide losses. In this study, lithium tantalate films were deposited on (0001) sapphire from lithium hexaethoxytantalate by chemical beam epitaxy. Characterization showed that films had nearly stoichiometric composition, epitaxial orientation, and a high degree of crystalline perfection. However, the films exhibited high optical waveguide losses. Additional characterization by TEM revealed that the films had a two dimensional grain structure with epitaxial variants related by translation and a twin orientation to the substrate. To better understand the nature of the heteroepitaxial growth of lithium tantalate on (0001) sapphire, a model was developed to explain the observed epitaxial orientations, misfit dislocation networks, and grain boundary structures of lithium tantalate on (0001) sapphire.

scholarly journals Analysis of NMR Spectral Analysis and Molecular Electronic Potential Maps on L-Arginine Phosphate Crystals for Non-Linear Optical Applications

2021 ◽  
Vol 12 (6) ◽  
pp. 8353-8366
Keyword(s):  
Natural Bond Orbital ◽  
Slow Evaporation ◽  
Crystalline Perfection ◽  
Charge Delocalization ◽  
Different Temperatures ◽  
Optical Applications ◽  
High Degree ◽  
Homo Lumo ◽  
Very High ◽  
Electronic Potential

L-Arginine Phosphate (LAP) is a possible material for applications involving nonlinear optical properties. Slow evaporation was used to generate single LAP crystals with a very high degree of transparency from an aqueous solution. The solubility of the pure and doped LAP crystals was measured at different temperatures in the double-distilled water. Natural bond orbital (NBO) research investigated the molecule's stability and charge delocalization. The HOMO-LUMO energies describe the charge transfer between molecules. The electrostatic potential of molecules has been investigated. The correlation found between crystalline perfection and SHG potency was mentioned.

TEM studies of solid-state reactions in sputter-deposited Nb/Al multilayer thin films

1996 ◽  
Vol 54 ◽  
pp. 1020-1021
Author(s):  
F. Ma ◽  
S. Vivekanand ◽  
K. Barmak ◽  
C. Michaelsen
Keyword(s):  
Thin Films ◽  
Solid State ◽  
Stoichiometric Composition ◽  
Analytical Electron Microscopy ◽  
Grain Structure ◽  
Solid State Reactions ◽  
Multilayer Thin Films ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sputter Deposited

Solid state reactions in sputter-deposited Nb/Al multilayer thin films have been studied by transmission and analytical electron microscopy (TEM/AEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The Nb/Al multilayer thin films for TEM studies were sputter-deposited on (1102)sapphire substrates. The periodicity of the films is in the range 10-500 nm. The overall composition of the films are 1/3, 2/1, and 3/1 Nb/Al, corresponding to the stoichiometric composition of the three intermetallic phases in this system.Figure 1 is a TEM micrograph of an as-deposited film with periodicity A = dA1 + dNb = 72 nm, where d's are layer thicknesses. The polycrystalline nature of the Al and Nb layers with their columnar grain structure is evident in the figure. Both Nb and Al layers exhibit crystallographic texture, with the electron diffraction pattern for this film showing stronger diffraction spots in the direction normal to the multilayer. The X-ray diffraction patterns of all films are dominated by the Al(l 11) and Nb(l 10) peaks and show a merging of these two peaks with decreasing periodicity.

Relationships Between Grain Boundary Structure and Material Properties

1980 ◽  
Vol 38 ◽  
pp. 366-369
Author(s):  
Brian Ralph ◽  
Barlow Claire ◽  
Nicola Ecob
Keyword(s):  
Grain Boundary ◽  
Material Properties ◽  
Main Property ◽  
Grain Structure ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Property Changes

This brief review seeks to summarize some of the main property changes which may be induced by altering the grain structure of materials. Where appropriate an interpretation is given of these changes in terms of current theories of grain boundary structure, and some examples from current studies are presented at the end of this paper.

scholarly journals Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys

2021 ◽  
Author(s):  
A. Bauer ◽  
M. Vollmer ◽  
T. Niendorf
Keyword(s):  
Martensitic Transformation ◽  
Grain Boundary ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Grain Boundaries ◽  
Tensile Tests ◽  
Image Correlation ◽  
Stress Concentrations ◽  
Grain Orientations ◽  
High Degree

AbstractIn situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is shown that grain boundaries lead to stress concentrations and, thus, to formation of unfavored martensite variants. Moreover, some martensite plates seem to penetrate the grain boundaries resulting in a high degree of irreversibility in this area. However, after a stable microstructural configuration is established in direct vicinity of the grain boundary, the transformation begins inside the neighboring grains eventually leading to a sequential transformation of all grains involved.

Frequency Dependent Electro-Optic Properties of Potassium Lithium Tantalate Niobate Single Crystal

2011 ◽  
Vol 425 (1) ◽  
pp. 82-89 ◽  
Author(s):  
Yang Li ◽  
Jun Li ◽  
Zhongxiang Zhou ◽  
Ruyan Guo ◽  
Amar Bhalla
Keyword(s):  
Single Crystal ◽  
Lithium Tantalate ◽  
Frequency Dependent ◽  
Electro Optic

scholarly journals Microstructure Evolution and Surface Cracking Behavior of Superheavy Forgings during Hot Forging

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zhenhua Wang ◽  
Hongpeng Xue ◽  
Deli Zhao
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Nuclear Power ◽  
Power Plants ◽  
Hot Forging ◽  
Model Material ◽  
Grain Structure ◽  
High Angle ◽  
Cracking Behavior

In recent years, superheavy forgings that are manufactured from 600 t grade ingots have been applied in the latest generation of nuclear power plants to provide good safety. However, component production is pushing the limits of the current free-forging industry. Large initial grain sizes and a low strain rate are the main factors that contribute to the deformation of superheavy forgings during forging. In this study, 18Mn18Cr0.6N steel with a coarse grain structure was selected as a model material. Hot compression and hot tension tests were conducted at a strain rate of 10−4·s−1. The essential nucleation mechanism of the dynamic recrystallization involved low-angle grain boundary formation and subgrain rotation, which was independent of the original high-angle grain boundary bulging and the presence of twins. Twins were formed during the growth of dynamic recrystallization grains. The grain refinement was not obvious at 1150°C. A lowering of the deformation temperature to 1050°C resulted in a fine grain structure; however, the stress increased significantly. Crack-propagation paths included high-angle grain boundaries, twin boundaries, and the insides of grains, in that order. For superheavy forging, the ingot should have a larger height and a smaller diameter.

scholarly journals Development of microstructure in the high-temperature deformation of ice

1996 ◽  
Vol 23 ◽  
pp. 293-302 ◽  
Author(s):  
Christopher J. L. Wilson ◽  
Yanhua Zhang
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Time Lapse ◽  
Grain Structure ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Grain Boundary Migration ◽  
Crystallographic Slip ◽  
Polycrystalline Ice ◽  
Time Lapse Photography

Microstructural changes in three sets of experiments involving crystallographic slip in anisotropic polycrystalline ice are described and interpreted with the aid of computer models. The development of microstructure was followed using time-lapse photography and transmitted light observations with deformation undertaken in plane strain and at a temperature of approximately –1°C. The deformation within a grain aggregate that accompanies axial shortening is always heterogeneous on a grainscale. The extent of inhomogeneity varies depending on the pre-existing grain structure and the way it can accommodate intragranular slip. Grain interactions are extremely important in determining the bulk deformation and the degree of grain-boundary migration. A consequence of shortening of the aggregate is the formation of high stresses between neighbouring grains and under the appropriate conditions there may be either grain-boundary migration or melting at these sites. Where a sample undergoes translation and shear during deformation, anisotropic grains in the appropriate orientation undergo bending. A buckle instability may then develop and much of the strain is accommodated by grains in easy-glide orientations. In such situations, the ice undergoes extensive recrystallization and grain growth that is concentrated in the areas of greatest buckling.

scholarly journals The Influence of Mg-Based Inclusions on the Grain Boundary Mobility of Austenite in SS400 Steel

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 370
Author(s):  
Chih-Ting Lai ◽  
Hsuan-Hao Lai ◽  
Yen-Hao Su ◽  
Fei-Ya Huang ◽  
Chi-Kang Lin ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
High Temperatures ◽  
Growth Curves ◽  
Solute Drag ◽  
Grain Structure ◽  
Growth Equation ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Boundary Velocity

In this study, the effects of the addition of Mg to the grain growth of austenite and the magnesium-based inclusions to mobility were investigated in SS400 steel at high temperatures. A high-temperature confocal scanning laser microscope (HT-CSLM) was employed to directly observe, in situ, the grain structure of austenite under 25 torr Ar at high temperatures. The grain size distribution of austenite showed the log-normal distribution. The results of the grain growth curves using 3D surface fitting showed that the n and Q values of the growth equation parameters ranged from 0.2 to 0.26 and from 405 kJ/mole to 752 kJ/mole, respectively, when adding 5.6–22 ppm of Mg. Increasing the temperature from 1150 to 1250 °C for 20 min and increasing the addition of Mg by 5.6, 11, and 22 ppm resulted in increases in the grain boundary velocity. The effects of solute drag and Zener pinning on grain boundary mobility were also calculated in this study.

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