HRTEM Image of Twin Structure in Nanocrystalline Platinum

1993 ◽  
Vol 51 ◽  
pp. 1160-1161
Author(s):  
Hong-Ming Lin ◽  
Chi-Ming Hsu ◽  
Ching-Shung Huang ◽  
Ming-Shyong Lay ◽  
Pee-Yew Lee
Keyword(s):  
Fourier Transformation ◽  
Nucleation And Growth ◽  
Twin Plane ◽  
Nanocrystalline Powders ◽  
Twin Structure ◽  
Bulk Materials ◽  
Helium Atmosphere ◽  
Neck Growth ◽  
Gas Condensation ◽  
The Individual

This paper presents recent result on the observation of microstructure of nanocrystalline platinum. Nanocrystalline powders of Pt are made by gas condensation method, and examined by using TEM and HRTEM. Twin structure is found first within the individual particle of as evaporated nanophase Pt particles which form twin during the nucleation and growth of particle. Twin also appears while neck growth take place during the sintering of as evaporated pt with Al2O3. The formation of these twins during sintering was due to the fact that the neck growth will induce a tensile stress which is high enough to pull the nanocrystalline powders to form twin structure. Twin plane of nanophase sintering Pt powder was identified by using the Fourier transformation as {111} plane. It is the same as usually found in fcc bulk materials.The pure nanocrystalline Pt particles with a diameter less than 100 nm had been produced by the gas evaporation in helium atmosphere.

scholarly journals Forming pressure effect on microstructure and mechanical properties of nanocrystalline aluminum synthesized by inert gas condensation

2019 ◽  
Vol 79 ◽  
pp. 02002
Author(s):  
Shangshu Wu ◽  
Zhou Yu ◽  
Junjie Wang ◽  
Hanxin Zhang ◽  
Chaoqun Pei ◽  
...  
Keyword(s):  
Room Temperature ◽  
High Vacuum ◽  
Inert Gas ◽  
Helium Atmosphere ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
In Situ Forming ◽  
Nanocrystalline Aluminum ◽  
Al Powder

The preparation of nanocrystalline aluminum (NC Al) was conducted in two steps. After the NC Al powder was synthesized by an Inert gas condensation (IGC) method in a helium atmosphere of 500 Pa, the NC Al powder was in-situ compacted into a pellet with a 10 mm diameter and 250 μm-300 μm thickness in a high vacuum (10-6 Pa-10-7 Pa) at room temperature. The NC Al samples were not exposed to air during the entire process. After the pressure reached 6 GPa, the relative density could reach 99.83%. The results showed that the grain size decreased with the increased of in-situ forming pressure. The NC Al samples present obvious ductile fracture, and the tensile properties were greatly changed with the increase of forming pressure.

Determination of twinning relationships between diopside dendrites

2010 ◽  
Vol 43 (6) ◽  
pp. 1393-1399
Author(s):  
Shan-Rong Zhao ◽  
Hai-Jun Xu ◽  
Hong-Wei Liu ◽  
Roger Mason ◽  
Hui-Fang Liu
Keyword(s):  
Point Group ◽  
Symmetry Plane ◽  
Twin Plane ◽  
Twin Structure ◽  
Electron Backscattered Diffraction ◽  
Twofold Axis ◽  
Relationship Analysis ◽  
The Third ◽  
Good Lattice

Electron backscattered diffraction, used to determine the orientations of dendritic crystals of synthetic diopside, revealed novel twinning relationships between three dendrite crystals. The three crystals, considered pairwise, are related by two twinning laws: for two pairs, twin plane {\overline 251} and twin axis 〈\overline 142〉 perpendicular to the twin plane; and for the third pair, twin plane {\overline 221} and twin axis 〈\overline 356〉 perpendicular to the twin plane. The twin axes and twin planes between the latter pair of crystals closely match the twofold axis and symmetry plane inside the third crystal. The distribution of the three dendrite crystals in the twin structure shows overall 2/msymmetry, so the point group of diopside controls the whole combination of three crystals. The twin laws have been analysed using the theories of Mallard and Friedel, and twin indices and twin obliquity calculated. The complex twin laws yield a good lattice coincidence, and lattice relationship analysis based on the {201} plane confirms the twin laws.

Twin structure in Yb:YAl3(BO3)4crystal

2001 ◽  
Vol 34 (5) ◽  
pp. 661-662 ◽  
Author(s):  
Shanrong Zhao ◽  
Jiyang Wang ◽  
Daliang Sun ◽  
Xiaobo Hu ◽  
Hong Liu
Keyword(s):  
Atomic Force Microscopy ◽  
Single Crystals ◽  
Chemical Etching ◽  
Laser Crystal ◽  
Frequency Doubling ◽  
Twin Plane ◽  
The Self ◽  
Twin Structure ◽  
Force Microscopy ◽  
Atomic Force

Twin structure is a defect in the self-frequency-doubling laser crystal material Yb:YAl3(BO3)4(YbYAB). Based on atomic force microscopy (AFM) observations, a check-like twin structure in YbYAB crystals is found. This kind of twin structure has three twin composition planes: (10\bar{1}1), (0\bar{1}11) and (\bar{1}101). These three twin composition planes result in a series of twin boundaries in two directions, forming a check-like pattern on each face. From the orientation of the chemical etching pits on each side of the twin boundary, it is found that the twin element is `twin plane ⊥yaxis', alternatively indicated as `twin plane {11\bar{2}0}'. The two single crystals composing the twin are a right form and a left form. This kind of twin is similar to the Brazil twin found in quartz.

Characterization of Nanophase Particle Aggregates by Transmission Electron Microscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 425-426
Author(s):  
G. Gonzalez ◽  
A. Freites ◽  
C. Rojas
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Condensed Matter ◽  
Nucleation And Growth ◽  
Bulk Materials ◽  
Transmission Electron ◽  
Particle Aggregates ◽  
Nanophase Materials ◽  
New Perspective

In the last few years there has been a growing interest in nanoparticles and nanophase materials. Nanoparticles are considered to be a new state of the condensed matter due to the high relation of atoms in the surface respect to the number of atoms in the volume, and their properties are neither those of atoms nor those of bulk materials.There are many interesting questions still to be answered and processes to be understood, from nucleation and growth processes to propertiesIn the present work we report the results of the fabrication of Mo, MoW and MoNi, particles by d.c. sputtering, under different pressures, from 0.2 torr to 0.8 torr. Their morphology, size distribution, aggregation and structure has been studied by Transmission Electron Microscopy.We analyzed our results contrasting them with those of Chow 1,2 and Birringer 3 and try to explain with a new perspective the formation mechanism of the particles, and the dependence of particle size with Ar pressure.

Nucleation and growth of Nb nanoclusters during plasma gas condensation

2013 ◽  
Vol 113 (23) ◽  
pp. 234307 ◽  
Author(s):  
K. R. Bray ◽  
C. Q. Jiao ◽  
J. N. DeCerbo
Keyword(s):  
Nucleation And Growth ◽  
Gas Condensation

Enhanced Thermoelectric Figure-of-merit at Room Temperature in Bulk Bi(Sb)Te(Se) With Grain Size of ∼100nm

2013 ◽  
Vol 1543 ◽  
pp. 93-98 ◽  
Author(s):  
Tsung-ta E. Chan ◽  
Rama Venkatasubramanian ◽  
James M. LeBeau ◽  
Peter Thomas ◽  
Judy Stuart ◽  
...  
Keyword(s):  
Grain Size ◽  
Mechanical Alloying ◽  
Grain Boundaries ◽  
Figure Of Merit ◽  
Room Temperature ◽  
High Energy ◽  
High Density ◽  
Nanocrystalline Powders ◽  
Bulk Materials ◽  
P Type

ABSTRACTGrain boundaries are known to be able to impede phonon transport in the material. In the thermoelectric application, this phenomenon could help improve the figure-of-merit (ZT) and enhance the thermal to electrical conversion. Bi2Te3 based alloys are renowned for their high ZT around room temperature but still need improvements, in both n- and p-type materials, for the resulting power generation devices to be more competitive. To implement high density of grain boundaries into the bulk materials, a bottom-up approach is employed in this work: consolidations of nanocrystalline powders into bulk disks. Nanocrystalline powders are developed by high energy cryogenic mechanical alloying that produces Bi(Sb)Te(Se) alloy powders with grain size in the range of 7 to 14 nm, which is about 25% finer compared to room temperature mechanical alloying. High density of grain boundaries are preserved from the powders to the bulk materials through optimized high pressure hot pressing. The consolidated bulk materials have been characterized by X-ray diffraction and transmission electron microscope for their composition and microstructure. They mainly consist of grains in the scale of 100 nm with some distributions of finer grains in both types of materials. Preliminary transport property measurements show that the thermal conductivity is significantly reduced at and around room temperature: about 0.65 W/m-K for the n-type BiTe(Se) and 0.85 W/m-K for the p-type Bi(Sb)Te, which are attributed to increased phonon scattering provided by the nanostructure and therefore enhanced ZT about 1.35 for the n-type and 1.21 for the p-type are observed. Detailed transport properties, such as the electrical resistivity, Seebeck coefficient and power factor as well as the resulting ZT as a function of temperature will be described.

scholarly journals X-ray studies bridge the molecular and macro length scales during the emergence of CoO assemblies

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lukas Grote ◽  
Cecilia A. Zito ◽  
Kilian Frank ◽  
Ann-Christin Dippel ◽  
Patrick Reisbeck ◽  
...  
Keyword(s):  
Classical Model ◽  
High Energy ◽  
Nucleation And Growth ◽  
Distribution Functions ◽  
High Energy Resolution ◽  
Sufficient Information ◽  
Length Scales ◽  
X Ray ◽  
Solvent Molecules ◽  
The Individual

AbstractThe key to fabricating complex, hierarchical materials is the control of chemical reactions at various length scales. To this end, the classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for assemblies of polyhedrally shaped CoO nanocrystals. Utilizing high energy-resolution fluorescence-detected X-ray absorption spectroscopy, we directly access the molecular level of the nanomaterial synthesis. We reveal that initially Co(acac)3 rapidly reduces to square-planar Co(acac)2 and coordinates to two solvent molecules. Combining atomic pair distribution functions and small-angle X-ray scattering we observe that, unlike a classical nucleation and growth mechanism, nuclei as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final spherical assemblies are smaller than 100 nm, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution.

Phase Transformation and Densification Behavior of Microwave Sintered γ-A12O3

1994 ◽  
Vol 347 ◽  
Author(s):  
John Freim ◽  
Joanna McKittrick ◽  
Joel Katz ◽  
Kurt Sickafus
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Growth Phase ◽  
Particle Morphology ◽  
Nucleation And Growth ◽  
Densification Behavior ◽  
Transformation Behavior ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Dense Bodies

ABSTRACTThe phase transformation and densification behavior of gas condensation synthesized γA12O3 sintered with microwave radiation has been studied. Nucleation and growth phase transformations, which produce α-A12O3 occurred as the material was heated through the temperature range of 800–1300°C. These phase transformations resulted in anomalous grain growth with a distinct change in particle morphology, crystallite size and surface area. A12O3 derived from a chemically synthesized boehmite precursor has been shown to exhibit the same nucleation and growth phase transformation behavior when conventionally heated. It is concluded that nanocrystalline γ or β alumina will not be a viable starting material for the production of dense bodies with grain sizes of less than 100 nm.

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