Atomic Structure of Alloys Close to Phase Transitions

1999 ◽  
Vol 580 ◽  
Author(s):  
G. Van Tendeloo ◽  
D. Schryvers
Keyword(s):  
Phase Transitions ◽  
Short Range ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Domain Formation ◽  
Ordering Effects ◽  
Resolution Electron ◽  
Short Range Ordering ◽  
Transition Effects ◽  
Martensitic Nucleation

AbstractPhase transitions are often accompanied by pre-transition effects. These effects have been studied on an atomic scale by high resolution electron microscopy. For the diffusion controled phase transitions we discuss short range ordering effects in Ni-Mo and Cu-Pd. For the displacive transitions we discuss the martensitic nucleation in Ni-Al and the nanoscale domain formation in the Ni-Ti R phase.

High resolution observations of short-range ordering in disordered Au4Mn alloys

1984 ◽  
Vol 42 ◽  
pp. 426-427
Author(s):  
Nobuo Tanaka ◽  
Ken-ichi Ohshima ◽  
Jinpei Harada ◽  
J.M. Cowley
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Diffuse Scattering ◽  
Short Range ◽  
High Resolution Electron Microscopy ◽  
Atomic Level ◽  
X Ray ◽  
Direct Observations ◽  
Resolution Electron ◽  
Short Range Ordering

Observation of short range ordered (SRO) state in disordered binary alloys is the interesting topic in the point of order-disorder transition. The observation and analysis have been made with X-ray and neutron diffraction techniques which can give the SRO-parameters. These techniques, however, give only the information of an averaged structure. The ordering process is localized, so direct observations in atomic level by high resolution electron microscopy is needed for the detailed analysis.In the present study, disordered Au4Mn alloys were investigated with high resolution electron microscopy for the analysis of the origin of the characteristic SRO diffuse scattering (Fig. 1). The material was prepared by quenching and thinned by electrolytic polishing for microscopic observations. The specimen was observed along <120> direction by JEOL-200CX electron microscope (E=200keV).

Short-Range-Ordering and Fe-Clustering in Au-Fe Alloys

1990 ◽  
Vol 205 ◽  
Author(s):  
Chen-Chia Chou ◽  
F.-R. Chen ◽  
C. M. Wayman
Keyword(s):  
Short Range ◽  
Early Stage ◽  
High Resolution Electron Microscopy ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Fe Content ◽  
Resolution Electron ◽  
Short Range Ordering ◽  
Fe Alloys ◽  
Microscopic Techniques

AbstractAs an “archtypal” spin-glass system, the local atomic arrangement in Au-Fe alloys is still a controversial subject. In the present experiment, Au-Fe alloys with Fe content from 10.7 to 33% were studied as to microstructure evolution, through various transmission electron microscopic techniques. Information derived from aging experiments using real and reciprocal spaces appears to suggest the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (1 1/2 0) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensifies decrease gradually as aging proceeds. After a certain period, (1 1/2 0) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (1 1/2 0) diffuse reflections. High resolution electron microscopy was also employed. The results are consistent with the arguments derived from aging experiments.

scholarly journals Hyalotekite, (Ba,Pb,K)4(Ca,Y)2Si8(B,Be)2(Si,B)2O28F, a tectosilicate related to scapolite: new structure refinement, phase transitions and a short-range ordered 3b superstructure

1998 ◽  
Vol 62 (1) ◽  
pp. 77-92 ◽  
Author(s):  
A. G. Christy ◽  
E. S. Grew ◽  
S. C. Mayo ◽  
M. G. Yates ◽  
D. I. Belakovskiy
Keyword(s):  
Phase Transitions ◽  
Short Range ◽  
Structure Refinement ◽  
High Resolution Electron Microscopy ◽  
Structural Formula ◽  
Cation Ordering ◽  
Resolution Electron ◽  
L 96 ◽  
Factor Data ◽  
Cation Sites

AbstractHyalotekite, a framework silicate of composition (Ba,Pb,K)4(Ca,Y)2Si8(B,Be)2 (Si,B)28F, is found in relatively high-temperature (⩾ 500°C) Mn skarns at Långban, Sweden, and peralkaline pegmatites at Dara-i-Pioz, Tajikistan. A new paragenesis at Dara-i-Pioz is pegmatite consisting of the Ba borosilicates leucosphenite and tienshanite, as well as caesium kupletskite, aegirine, pyrochlore, microcline and quartz. Hyalotekite has been partially replaced by barylite and danburite. This hyalotekite contains 1.29–1.78 wt.% Y2O3, equivalent to 0.172–0.238 Y pfu or 8–11% Y on the Ca site; its Pb/(Pb+Ba) ratio ranges 0.36–0.44. Electron microprobe F contents of Långban and Dara-i-Pioz hyalotekite range 1.04–1.45 wt.%, consistent with full occupancy of the F site. A new refinement of the structure factor data used in the original structural determination of a Långban hyalotekite resulted in a structural formula, (Pbl.96Bal.86K0.18)Ca2(B1.76Be0.24)(Sil.56B0.44)Si8O28F, consistent with chemical data and all cations with positive-definite thermal parameters, although with a slight excess of positive charge (+57.14 as opposed to the ideal +57.00). An unusual feature of the hyalotekite framework is that 4 of 28 oxygens are non-bridging; by merging these 4 oxygens into two, the framework topology of scapolite is obtained. The triclinic symmetry of hyalotekite observed at room temperature is obtained from a hypothetical tetragonal parent structure via a sequence of displacive phase transitions. Some of these transitions are associated with cation ordering, either Pb–Ba ordering in the large cation sites, or B–Be and Si–B ordering on tetrahedral sites. Others are largely displacive but affect the coordination of the large cations (Pb, Ba, K, Ca). High-resolution electron microscopy suggests that the undulatory extinction characteristic of hyalotekite is due to a fine mosaic microstructure. This suggests that at least one of these transitions occurs in nature during cooling, and that it is first order with a large volume change. A diffuse superstructure observed by electron diffraction implies the existence of a further stage of short-range cation ordering which probably involves both (Pb,K)–Ba and (BeSi,BB)–BSi.

Limits for high-resolution electron microscopy of inorganic materials?

1987 ◽  
Vol 45 ◽  
pp. 4-5
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Inorganic Materials ◽  
Atomic Scale ◽  
Resolution Limit ◽  
Contrast Transfer Function ◽  
Existing Problems ◽  
Resolution Electron ◽  
Electron Microscopes

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

Atomic Scale Structure-Property Relationships of Defects and Interfaces in Ceramics

1998 ◽  
Vol 4 (S2) ◽  
pp. 556-557
Author(s):  
S. Stemmer ◽  
G. Duscher ◽  
E. M. James ◽  
M. Ceh ◽  
N.D. Browning
Keyword(s):  
Point Defects ◽  
High Resolution Electron Microscopy ◽  
Complete Characterization ◽  
Atomic Scale ◽  
Structure Property ◽  
Defect Engineering ◽  
Impurity Atoms ◽  
Structure Property Relationships ◽  
Resolution Electron ◽  
Scale Composition

The evaluation of the two dimensional projected atom column positions around a defect or an interface in an electronic ceramic, as it has been performed in numerous examples by (quantitative) conventional high-resolution electron microscopy (HRTEM), is often not sufficient to relate the electronic properties of the material to the structure of the defect. Information about point defects (vacancies, impurity atoms), and chemistry or bonding changes associated with the defect or interface is also required. Such complete characterization is a necessity for atomic scale interfacial or defect engineering to be attained.One instructive example where more than an image is required to understand the structure property relationships, is that of grain boundaries in Fe-doped SrTi03. Here, the different formation energies of point defects cause a charged barrier at the boundary, and a compensating space charge region around it. The sign and magnitude of the barrier depend very sensitively on the atomic scale composition and chemistry of the boundary plane.

X-Ray-Optical Multilayer Structures Studied Using High Resolution Electron Microscopy.

1986 ◽  
Vol 77 ◽  
Author(s):  
Mary Beth Stearns ◽  
Amanda K. Petford-Long ◽  
C.-H. Chang ◽  
D. G. Stearns ◽  
N. M. Ceglio ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Substrate Surface ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Degree Of Crystallinity ◽  
Multilayer Systems ◽  
Layer Width ◽  
X Ray ◽  
Resolution Electron

ABSTRACTThe technique of high resolution electron microscopy has been used to examine the structure of several multilayer systems (MLS) on an atomic scale. Mo/Si multilayers, in use in a number of x-ray optical element applications, and Mo/Si multilayers, of interest because of their magnetic properties, have been imaged in cross-section. Layer thicknesses, flatness and smoothness have been analysed: the layer width can vary by up to 0.6nm from the average value, and the layer flatness depends on the quality of the substrate surface for amorphous MLS, and on the details of the crystalline growth for the crystalline materials. The degree of crystallinity and the crystal orientation within the layers have also been investigated. In both cases, the high-Z layers are predominantly crystalline and the Si layers appear amorphous. Amorphous interfacial regions are visible between the Mo and Si layers, and crystalline cobalt suicide interfacial regions between the Co and Si layers. Using the structural measurements obtained from the HREM results, theoretical x-ray reflectivity behaviour has been calculated. It fits the experimental data very well.

Atomistic Processes of Phase Transformation and Dynamic Recrystallization during Hot-Working of Intermetallic Titanium Aluminides

2007 ◽  
Vol 558-559 ◽  
pp. 465-470
Author(s):  
Fritz Appel ◽  
Michael Oehring ◽  
Jonathan H.D. Paul
Keyword(s):  
Phase Transformation ◽  
Dynamic Recrystallization ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Equilibrium Phase ◽  
High Resolution Electron Microscopy ◽  
Hot Working ◽  
Atomic Scale ◽  
Resolution Electron ◽  
Deformation State

Intermetallic titanium aluminide alloys are multiphase assemblies with complex microstructure and constitution, involving the phases γ(TiAl), α2(Ti3Al), β, and B2. The earlier stages of phase transformation and dynamic recrystallization occurring upon hot-working of such an alloy were investigated at the atomic scale by high-resolution electron microscopy. Accordingly, the conversion of the microstructure is triggered by heterogeneities in the deformation state and non-equilibrium phase composition. The β/B2 phase is apparently unstable under tetragonal distortion, which gives rise to the formation of the B19 phase via distinct shuffle displacements. These processes lead to a modulated microstructure, which is comprised of several stable and metastable phases. The phase transformations are accomplished by the propagation and coalescence of ledges. Large and broad ledges can apparently easily be rearranged into intermediate metastable structures, which serve as precursor for the nucleation of new grains.

Electron microscopic interfacial analysis of diamond film grown on silicon substrate

1996 ◽  
Vol 11 (7) ◽  
pp. 1783-1786 ◽  
Author(s):  
N. Jiang ◽  
A. Hatta ◽  
T. Ito ◽  
Z. Zhang ◽  
T. Sasaki ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Amorphous Solid ◽  
High Resolution Electron Microscopy ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Recrystallization Process ◽  
Electron Microscopic ◽  
Precursor Phase ◽  
Resolution Electron ◽  
Hot Filament

We have investigated the near-interface characterization of diamond films grown on Si(100) substrates by means of a hot-filament chemical-vapor-deposition (HFCVD) method using high-resolution-electron microscopy (HREM). Atomic scale study of the diamond/Si interface reveals that on the top of the amorphous intermediate layer, there exists a precursor phase which seems to be a diamond-like structure, which provides a suitable site for subsequent diamond nucleation. High density crystal defects directly originate from the precursor phase. HREM images also reveal that during the deposition Si recrystallizes in some damaged areas left by pretreatment, such as scratching grooves. In the recrystallization process twins and microtwins can be formed, and amorphous solid is left in the Si crystals.

Atomic Scale Aluminum and Strain Distribution in a Gan/AlxGa1−XN Heterostructure

1997 ◽  
Vol 482 ◽  
Author(s):  
Christian Kisielowski ◽  
Olaf Schmidt ◽  
Jinwei Yang
Keyword(s):  
Three Dimensional ◽  
Chemical Vapor ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Organic Chemical ◽  
Well Test ◽  
Lattice Constants ◽  
Resolution Electron ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition

AbstractA GaN/AlxGalxN multi-quantum well test structure with Al concentrations 0 ≤ xAl ≤ 1 was utilized to investigate the growth of AlxGal–xN barrier layers deposited by metal organic chemical vapor deposition (MOCVD). A transition from a two dimensional (2D) to a three dimensional (3D) growth mode was observed in AlxGa1–xN barriers with XAl ≥ 0.75. It is argued that the transition occurs because of growth at temperatures that are low compared with the materials melting points Tmelt. The resulting rough AlxGa1–xN surfaces can be planarized by overgrowth with GaN. Quantitative high resolution electron microscopy (HREM) was applied to measure composition and strain profiles across the GaN/AlxGa1−xN stacks at an atomic level. The measurements reveal a substantial variation of lattice constants at the AlxGa1−xN/GaN interfaces that is attributed to an Al accumulation.

Atomic Scale Study of Cosi/Si (111) and CoSi2/Si (111) Interfaces

1989 ◽  
Vol 159 ◽  
Author(s):  
A. Catana ◽  
M. Heintze ◽  
P.E. Schmid ◽  
P. Stadelmann
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
High Resolution ◽  
Orientation Relationship ◽  
Cross Sections ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Type B ◽  
Initial Stage ◽  
Resolution Electron

ABSTRACTHigh Resolution Electron Microscopy (HREM) was used to study microstructural changes related to the CoSi/Si-CoSi/CoSi2/Si-CoSi2/Si transformations. CoSi is found to grow epitaxially on Si with [111]Si // [111]CoSi and < 110 >Si // < 112 >CoSi. Two CoSi non-equivalent orientations (rotated by 180° around the substrate normal) can occur in this plane. They can be clearly distinguished by HRTEM on cross-sections ( electron beam along [110]Si). At about 500°C CoSi transforms to CoSi2. Experimental results show that the type B orientation relationship satisfying [110]Si // [112]CoSi is preserved after the initial stage of CoSi2 formation. At this stage an epitaxial CoSi/CoSi2/Si(111) system is obtained. The atomic scale investigation of the CoSi2/Si interface shows that a 7-fold coordination of the cobalt atoms is observed in both type A and type B epitaxies.

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