scholarly journals Evolution of Pressure-induced Shear Amorphization in Rare-earth Hexaboride

2021 ◽  
Author(s):  
Rajamallu Karre ◽  
Yidi Shen ◽  
Shuangxi Song ◽  
Yixuan Hu ◽  
Simanta Lahkar ◽  
...  
Keyword(s):  
High Pressure ◽  
Rare Earth ◽  
Density Functional ◽  
Shear Bands ◽  
Structural Evolution ◽  
Decisive Role ◽  
Damage Mechanism ◽  
Metallic State ◽  
Transmission Electron ◽  
Europium Hexaboride

Abstract Research on rare-earth hexaborides mainly focuses on tuning the electronic structure from insulating-to-metallic state and vice versa (referred as exotic phenomena) by high pressure experiments via displacive phase transformations, however, the structural evolution that contributing to this underlying failure mechanism remains not well understood. Herein, we examined the pressure induced structural evolution through a model system of europium hexaboride (EuB6). Transmission electron microscopy reveal that the nanoscale amorphous shear bands mediated by dislocations play a decisive role in deformation failure of EuB6 subjected to high pressure nanoidentation at room temperature. Density functional theory simulations confirm that these amorphous bands evolve by breaking B-B bonds within B6 octahedron of EuB6 during shear deformation. Our results underscore an important damage mechanism in hard and fragile hexaborides at high shear pressures.

Structural evolution of heavy rare Earth-based metal glass under high pressure

2020 ◽  
Vol 33 (3) ◽  
pp. 035405
Author(s):  
Wang Yongyong ◽  
Zhang Panpan ◽  
Li Qing ◽  
Li Gong
Keyword(s):  
High Pressure ◽  
Rare Earth ◽  
Structural Evolution ◽  
Heavy Rare Earth

Strengthening of Nickel Deformed by High Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 417-421 ◽  
Author(s):  
Hong Wang Zhang ◽  
X. Huang ◽  
Niels Hansen ◽  
Reinhard Pippan ◽  
Michael Zehetbauer
Keyword(s):  
High Pressure ◽  
Cold Rolling ◽  
High Pressure Torsion ◽  
Structural Evolution ◽  
Longitudinal Section ◽  
High Angle ◽  
Microstructural Parameters ◽  
Transmission Electron ◽  
Structure Relationship ◽  
Von Mises

The strength of a deformed metal depends on the content of high angle boundaries, low angle dislocation boundaries and the dislocations between the boundaries. High angle boundaries contribute by Hall-Petch strengthening, whereas for the low angle dislocation boundaries and dislocations between boundaries the strengthening is proportional to the square root of the dislocation density. Based on an assumption of additivity of these contributions, the flow stresses of metals deformed by cold rolling have been calculated successfully. In the present investigation pure Ni (99.9%) has been deformed by high pressure torsion (HPT) to von Mises strains of 0.9, 1.7, 8.7 and 12. The strength of the HPT Ni has been determined by Vickers microhardness (HV) measurements and the microstructural parameters have been determined by transmission electron microscope (TEM) in the longitudinal section. HPT has been compared with deformation by cold rolling and torsion based on the structural evolution with strain and the stress-structure relationship. Based on an assumption of a linear additivity of boundary strengthening and dislocation strengthening, good agreement has been found between the calculated and the experimental flow stress.

AB INITIO STUDY OF STRUCTURAL PROPERTIES OF INTERMETALLIC COMPOUNDS PtX (X = Si, Ge, Sn AND Pb) UNDER HIGH PRESSURE

2012 ◽  
Vol 26 (18) ◽  
pp. 1250127
Author(s):  
C. Y. LI ◽  
Z. H. YU ◽  
T. Q. LÜ
Keyword(s):  
High Pressure ◽  
Intermetallic Compounds ◽  
Density Functional ◽  
Pressure Effect ◽  
Applied Pressure ◽  
Structural Evolution ◽  
Anisotropic Behavior ◽  
Pressure Derivative ◽  
Functional Theory ◽  
Principle Density Functional Theory

High pressure effect on the structural evolution properties of intermetallic compounds PtX (X = Si, Ge, Sn AND Pb ) was studied based on the first principle density functional theory. The compressibility of PtSi and PtGe under high pressure presents anisotropic behavior. The crystal stacking characteristic of the PtX (X = Si and Ge ) along the three axes may be responsible for their anisotropic axial compressibility under high pressure. The sequence of axial compressibility for PtSi is c < a < b, whereas PtGe exhibits the sequence of a < c < b. The pressure derivative of c/a was qualified to be 8.92×10-4 GPa -1 and 1.38×10-3 GPa -1 for PtSn and PtPb , respectively. The applied pressure stabilized the crystal structures of PtSn and PtPb .

High Pressure Torsion of Intermetallic Zr3Al

2008 ◽  
Vol 584-586 ◽  
pp. 553-558 ◽  
Author(s):  
David Geist ◽  
Christian Rentenberger ◽  
Hans Peter Karnthaler
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Structural Evolution ◽  
Nanocrystalline Structure ◽  
Temperature Dependent ◽  
Transmission Electron ◽  
Ordered Alloys ◽  
Grain Fragmentation ◽  
Shear Strains

The L12-structured intermetallic compound Zr3Al can be rendered amorphous easily by several techniques. In the present study the structural evolution during high pressure torsion (HPT) was investigated systematically by transmission electron microscopy (TEM) methods. Zr3Al samples were deformed at room temperature to different grades of deformation up to shear strains of 140 000%. TEM investigations revealed that the tendency to grain fragmentation, disordering and the formation of a nanocrystalline structure is weak compared to other L12 ordered alloys like Ni3Al. In addition, an amorphous phase has not been encountered. The present results differ strongly from previous ones obtained from ball-milled materials. Possible reasons for the different behavior are discussed on the basis of the temperature dependent dissociation scheme of the superlattice dislocations gliding in Zr3Al.

Structural Evolution on the Cross-Section of an AZ31 Magnesium Alloy Processed by High-Pressure Torsion

2010 ◽  
Vol 667-669 ◽  
pp. 247-252 ◽  
Author(s):  
Roberto B. Figueiredo ◽  
Terence G. Langdon
Keyword(s):  
High Pressure ◽  
Magnesium Alloy ◽  
Cross Section ◽  
High Pressure Torsion ◽  
Shear Bands ◽  
Structural Evolution ◽  
Grain Structure ◽  
Az31 Magnesium Alloy ◽  
Average Grain Size ◽  
The Cross

Disks of an AZ31 magnesium alloy were processed by High-Pressure Torsion (HPT) at 463 K to different numbers of rotations. The grain structure was evaluated along the cross-section of the disks using optical microscopy. Significant heterogeneities in the average grain size were observed in areas of the disks which were located at similar distances to the center but at different distances from the surface. Moreover, different grain structures were observed in neighboring areas and shear bands occurred at several locations in the disks. Microhardness tests revealed differences in the strength of the material as a function of the distance to the surface. An analysis of the grain structure and hardness distribution suggests the occurrence of flow localization in HPT processing.

scholarly journals Origin of enhanced chemical precompression in cerium hydride $$\hbox {CeH}_{{9}}$$

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Hyunsoo Jeon ◽  
Chongze Wang ◽  
Seho Yi ◽  
Jun-Hyung Cho
Keyword(s):  
Density Functional Theory ◽  
High Pressure ◽  
Rare Earth ◽  
Rare Earth Metal ◽  
Density Functional ◽  
Metal Hydrides ◽  
Earth Metal ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Valence States

Abstract The rare-earth metal hydrides with clathrate structures have been highly attractive because of their promising high-$$T_{\rm{c}}$$ T c superconductivity at high pressure. Recently, cerium hydride $$\hbox {CeH}_9$$ CeH 9 composed of Ce-encapsulated clathrate H cages was synthesized at much lower pressures of 80–100 GPa, compared to other experimentally synthesized rare-earth hydrides such as $$\hbox {LaH}_{{10}}$$ LaH 10 and $$\hbox {YH}_6$$ YH 6 . Based on density-functional theory calculations, we find that the Ce 5p semicore and 4f/5d valence states strongly hybridize with the H 1s state, while a transfer of electrons occurs from Ce to H atoms. Further, we reveal that the delocalized nature of Ce 4f electrons plays an important role in the chemical precompression of clathrate H cages. Our findings not only suggest that the bonding nature between the Ce atoms and H cages is characterized as a mixture of ionic and covalent, but also have important implications for understanding the origin of enhanced chemical precompression that results in the lower pressures required for the synthesis of $$\hbox {CeH}_9$$ CeH 9 .

Microstructural Study of Diamond Deformed Under High Pressure and Temperature

1985 ◽  
Vol 43 ◽  
pp. 230-231
Author(s):  
E. F. Koch
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Lattice Structure ◽  
Diamond Particle ◽  
Polycrystalline Diamond ◽  
Sintering Process ◽  
Ion Milling ◽  
Sintered Compact ◽  
Transmission Electron ◽  
High Pressure Sintering

Because of the extremely rigid lattice structure of diamond, generating new dislocations or moving existing dislocations in diamond by applying mechanical stress at ambient temperature is very difficult. Analysis of portions of diamonds deformed under bending stress at elevated temperature has shown that diamond deforms plastically under suitable conditions and that its primary slip systems are on the ﹛111﹜ planes. Plastic deformation in diamond is more commonly observed during the high temperature - high pressure sintering process used to make diamond compacts. The pressure and temperature conditions in the sintering presses are sufficiently high that many diamond grains in the sintered compact show deformed microtructures.In this report commercially available polycrystalline diamond discs for rock cutting applications were analyzed to study the deformation substructures in the diamond grains using transmission electron microscopy. An individual diamond particle can be plastically deformed in a high pressure apparatus at high temperature, but it is nearly impossible to prepare such a particle for TEM observation, since any medium in which the diamond is mounted wears away faster than the diamond during ion milling and the diamond is lost.

Microstructural characterization of a cast RENi5-based alloy

1993 ◽  
Vol 51 ◽  
pp. 1176-1177
Author(s):  
G. M. Micha ◽  
L. Zhang
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Microstructural Characterization ◽  
Binary Compound ◽  
Nickel Metal ◽  
Cast Material ◽  
Nickel Metal Hydride ◽  
Transmission Electron ◽  
Cast Condition

RENi5 (RE: rare earth) based alloys have been extensively evaluated for use as an electrode material for nickel-metal hydride batteries. A variety of alloys have been developed from the prototype intermetallic compound LaNi5. The use of mischmetal as a source of rare earth combined with transition metal and Al substitutions for Ni has caused the evolution of the alloy from a binary compound to one containing eight or more elements. This study evaluated the microstructural features of a complex commercial RENi5 based alloy using scanning and transmission electron microscopy.The alloy was evaluated in the as-cast condition. Its chemistry in at. pct. determined by bulk techniques was 12.1 La, 3.2 Ce, 1.5 Pr, 4.9 Nd, 50.2 Ni, 10.4 Co, 5.3 Mn and 2.0 Al. The as-cast material was of low strength, very brittle and contained a multitude of internal cracks. TEM foils could only be prepared by first embedding pieces of the alloy in epoxy.

scholarly journals Shedding Light on the Chemistry and the Properties of Münchnone Functionalized Graphene

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1629
Author(s):  
Giulia Neri ◽  
Enza Fazio ◽  
Antonia Nostro ◽  
Placido Giuseppe Mineo ◽  
Angela Scala ◽  
...  
Keyword(s):  
Density Functional ◽  
Antimicrobial Properties ◽  
Biological Properties ◽  
Azomethine Ylide ◽  
Functionalized Graphene ◽  
Functional Theory ◽  
Pyrrole Derivatives ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Direct Functionalization

Münchnones are mesoionic oxazolium 5-oxides with azomethine ylide characteristics that provide pyrrole derivatives by a 1,3-dipolar cycloaddition (1,3-DC) reaction with acetylenic dipolarophiles. Their reactivity was widely exploited for the synthesis of small molecules, but it was not yet investigated for the functionalization of graphene-based materials. Herein, we report our results on the preparation of münchnone functionalized graphene via cycloaddition reactions, followed by the spontaneous loss of carbon dioxide and its further chemical modification to silver/nisin nanocomposites to confer biological properties. A direct functionalization of graphite flakes into few-layers graphene decorated with pyrrole rings on the layer edge was achieved. The success of functionalization was confirmed by micro-Raman and X-ray photoelectron spectroscopies, scanning transmission electron microscopy, and thermogravimetric analysis. The 1,3-DC reactions of münchnone dipole with graphene have been investigated using density functional theory to model graphene. Finally, we explored the reactivity and the processability of münchnone functionalized graphene to produce enriched nano biomaterials endowed with antimicrobial properties.

scholarly journals High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 724
Author(s):  
Sara Massardo ◽  
Alessandro Cingolani ◽  
Cristina Artini
Keyword(s):  
Thin Films ◽  
High Pressure ◽  
Rare Earth ◽  
Ionic Conductivity ◽  
Bulk Material ◽  
Threshold Temperature ◽  
Doped Ceria ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rare Earth Doped

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films.

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