scholarly journals Novel Fe hydrides and magnetism in the Fe-H system at high pressures

2021 ◽  
Author(s):  
Ilya Kupenko ◽  
Elena Bykova ◽  
Denis M. Vasiukov ◽  
Georgios Aprilis ◽  
Valerio Cerantola ◽  
...  
Keyword(s):  
High Pressures ◽  
High Temperature Superconductivity ◽  
Magnetic Behavior ◽  
Face Centered Cubic ◽  
High Hydrogen ◽  
Range Magnetic Order ◽  
Face Centered ◽  
Storage Technologies ◽  
Long Range Magnetic Order ◽  
Hexagonal Closed Packed

Abstract The structure and properties of metal-hydrides at extreme conditions is key to the understanding of hydrogen-storage technologies, high-temperature superconductivity, and the dynamics of planetary cores. Here we investigate the phase relations and magnetic properties of iron hydrides, including two novel FeHx compounds, up to 63 GPa and 1800 K by Synchrotron Mössbauer Source spectroscopy and single-crystal X-ray diffraction. We observe the formation of a novel monoclinic iron hydride phase Fe2H∼3 at 63 GPa and 1000 K, which breaks down to a stoichiometric hexagonal closed packed FeH phase upon decompression below 52 GPa at 300 K. The long-range magnetic order in the two newly-synthetized phases persists to higher pressures compared to the well-known double hexagonal closed packed and face-centered cubic phases of FeH. The formation of magnetic Fe-H phases with high hydrogen concentration may influence the magnetic behavior of planetary metallic cores.

Comparison of Trapping Sites of Anthracene in Hexagonal and Cubic Argon Matrices: a Molecular Dynamics Study

2000 ◽  
Vol 214 (6) ◽  
Author(s):  
D. Horinek ◽  
B. Dick
Keyword(s):  
Molecular Dynamics ◽  
Random Search ◽  
Face Centered Cubic ◽  
Host Crystal ◽  
Unique Site ◽  
The Face ◽  
Face Centered ◽  
Argon Matrices ◽  
Hexagonal Closed Packed ◽  
Trapping Sites

Geometries and energies for possible trapping sites of anthracene in hexagonal closed packed (hcp) argon matrices have been calculated and compared to corresponding trapping sites calculated for the face centered cubic fcc argon host. The random search method (RSM) has been applied which combines statistical and molecular dynamics (MD) components in the generation of initial geometries and their relaxation. A total of 1322 runs yielded 12 unique site structures. In none of them the anthracene is located in the {111}-plane of the host crystal, in contrast to the situation found for the fcc host structure.

scholarly journals Synthesis of Non-Stoichiometric (TiNb)C0.5 with High Hardness and Fracture Toughness under HTHP

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1219
Author(s):  
Zhichao Zhang ◽  
Hu Tang ◽  
Yujiao Ke ◽  
Yu Li ◽  
Xiaochen Jiao ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
High Pressures ◽  
Raw Materials ◽  
High Hardness ◽  
High Strength ◽  
Phase Identification ◽  
Face Centered Cubic ◽  
Covalent Bonds ◽  
Synthetic Strategy ◽  
Face Centered

Nonstoichiometric TiC0.5 and (TiNb)0.5 powders were prepared by the mechanical alloying process using Ti, Nb, and TiC powders as raw materials. Furthermore, the as-prepared TiC0.5 and (TiNb)0.5 powders were used as initial materials to fabricate TiC0.5 and (TiNb)0.5 compacts under high pressures and high temperatures (HTHP) of 5.5 GPa and 1200–1550 °C for 5 min. Phase identification and microstructure of the mechanical-alloyed powders and the sintered TiC0.5 and (TiNb)0.5 compacts were realized by an X-ray diffractometer and scanning electron microscope. The results indicate that the as-prepared TiC0.5 and (TiNb)0.5 powders have a similar crystal structure of face-centered cubic (FCC) to TiC. The sintered (TiNb)0.5 compact has good Vickers hardness (~16 GPa), and notably, excellent fracture toughness (~7.3 MPa·m1/2). The non-stoichiometric compound not only reduced the sintering temperature of covalent compounds, but also greatly enhanced the mechanical properties of the materials. Thus, we have provided a novel synthetic strategy for the production of a compound with high-strength covalent bonds.

Improvement of Surface Cracking Risks by Controlling Dilution of Cobalt-Based Hardfacings

2021 ◽  
Author(s):  
Takashi Yokoyama ◽  
Takayuki Kurimura ◽  
Noriyuki Sakakibara ◽  
Fumiyuki Suzuki
Keyword(s):  
Base Material ◽  
Strength Properties ◽  
Face Centered Cubic ◽  
Test Results ◽  
Steam Turbines ◽  
Surface Cracking ◽  
Base Materials ◽  
Face Centered ◽  
Reduced Surface ◽  
Hexagonal Closed Packed

Abstract Cobalt-based hardfacings have been widely applied to the main valve seats of steam turbines for the purpose of improving durability. With the aim of decreasing the surface cracking risks of the hardfacings, the dilution of the hardfacing on their surface was controlled and the properties of the dilution-controlled materials were investigated in this study. Mixtures of cobalt-based hardfacings and base materials were cast in order to simulate the dilution of base material to hardfacing, which occurs in the process such as PTA welding. It was confirmed that the grain size matched that produced by PTA welding by controlling the cooling rate. To investigate the effect of aging on the microstructures and mechanical properties of the cast samples, the samples were aged in electric furnaces where the temperature was controlled to the steam temperature of steam turbines and above. The test results show that the phase transitioned from face-centered cubic to hexagonal closed-packed in low-dilution samples, while carbides precipitated along the grain boundaries in high-dilution samples after aging. Both samples showed an increase in hardness and reduction in ductility and fracture toughness. In addition, the variation in microstructures and strength properties was suppressed for a 20 % dilution sample. To validate the influence of dilution as investigated with the cast samples, test specimens were machined from the surface and bottom layers of multi-layered hardfacing that had different dilutions by PTA welding. It was confirmed that the influence of dilution on the strength properties of hardfacing layers had a similar tendency to the cast samples. The results above lead to the possibility of reducing the surface cracking risks by controlling the dilution of hardfacings and suppressing embrittlement after aging. We have applied dilution-controlled hardfacings to steam valves and successfully reduced surface cracking.

Crystallographic Structure of Cobalt Films on CU (100)

1993 ◽  
Vol 313 ◽  
Author(s):  
O. Heckmann ◽  
H. Magnan ◽  
P. Le Fevre ◽  
D. Chandesris
Keyword(s):  
Normal Incidence ◽  
Grazing Incidence ◽  
Lattice Parameter ◽  
Crystallographic Structure ◽  
Face Centered Cubic ◽  
Fee Structure ◽  
The Face ◽  
The Mean ◽  
Face Centered ◽  
Hexagonal Closed Packed

ABSTRACTThe stable structure of cobalt is hexagonal closed packed (hep), but cobalt can be stabilized in the face centered cubic structure (fee) by epitaxy on Cu (100). These films are ferromagnetic with [110] in plane easy axis. The Magnetic anisotropies of these films strongly depend on their structure, and in particular to the possible deviation from the isotropie fee structure. We have studied these films by surface EXAF.S. By recording the spectra both in normal incidence and in grazing incidence we have shown that the Co/Cu (100) films have a face centered tetragonal structure: the mean nearest neighbour distance parallel to the surface is 2.55 Å (same value as in bulk copper) and the interlayer bonds length is 2.50 Å (same value as in bulk cobalt). We conclude that the films are in perfect epitaxy on copper (100) with a contraction of the lattice parameter perpendicular to the surface of 4%. A constant tetragonalization is observed for films of 2 to 15 Monolayers.

Magnetic and Magnetoresistance Properties of (Co/Ge)n Films

2015 ◽  
Vol 233-234 ◽  
pp. 423-426
Author(s):  
Gennady Patrin ◽  
Igor Turpanov ◽  
Ekaterina Maruschenko ◽  
Konstantin Patrin ◽  
Alexander Kobyakov ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Magnetic Layer ◽  
Magnetic Behavior ◽  
The Other ◽  
Dead Layer ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Ferromagnetic Order ◽  
Face Centered ◽  
Magnetic And Electrical Properties

The magnetic and electrical properties of (Co/Ge)nfilms are experimentally studied. It is established that at the Co/Ge interfacean intermediate magnetic layer forms. Twophases of cobalt, one is a face-centered cubic phase and the other ispresumably a Co–Ge alloy with a weakly ferromagnetic order, have been found toexist. A “dead” layer no more than 2 nm in thickness is formed at the interface.This layer affects the magnetic behavior andmagnetoresistive effect in the investigated structures.

Size and Composition Effects in the Structure and Properties of Polymer-Protected Bimetallic Particles

2001 ◽  
Vol 704 ◽  
Author(s):  
Marie-José Casanove ◽  
Pierre Lecante ◽  
Marie-Claire Fromen ◽  
Marc Respaud ◽  
David Zitoun ◽  
...  
Keyword(s):  
Structural Evolution ◽  
Magnetic Behavior ◽  
Organic Matrix ◽  
Face Centered Cubic ◽  
Bimetallic Particles ◽  
Close Packed Structure ◽  
Hexagonal Close Packed Structure ◽  
The Face ◽  
Face Centered ◽  
Size Dispersion

AbstractWe investigate the structural evolution of PtRu and CoRh ultra fine bimetallic particles as a function of their composition in the whole range of stoichiometry. Isolated particles embedded in an organic matrix are synthesized using chemical techniques in mild conditions. Their size, dispersion and structure are analyzed by HRTEM, WAXS and EXAFS techniques. The magnetic behavior of cobalt-based alloys is investigated by SQUID magnetometry. In the PtRu alloys, we demonstrate the role of composition in the structural transition from the face-centered cubic to the hexagonal close packed structure in nanoparticles and detail the mechanism of the transition. We point out the effect of size reduction and core-shell atomic distribution in the structure and the enhanced magnetization in CoRh bimetallic particles.

HR-TEM Studies of FePt Nanoparticles by Exit Wave Reconstruction

2007 ◽  
Vol 998 ◽  
Author(s):  
Daniela Sudfeld ◽  
Olga Dmitrieva ◽  
Nina Friedenberger ◽  
Guenter Dumpich ◽  
Michael Farle ◽  
...  
Keyword(s):  
Data Storage ◽  
Density Functional ◽  
Lattice Structure ◽  
Magnetic Behavior ◽  
Magnetic Data ◽  
Fept Nanoparticles ◽  
Face Centered Cubic ◽  
Scattered Electron ◽  
Transmission Electron ◽  
Face Centered

ABSTRACTFePt nanoparticles are promising materials for high-density magnetic data storage media [1] and bio-medical applications such as drug-targeting and hyperthermia [2]. To understand their magnetic properties [3] it is essential to get insights into the lattice structure of isolated nanoparticles which influence the magnetic behavior.Typically, lattice fringes are observed with high-resolution transmission electron microscopy (HR-TEM). In this case delocalization effects disturb imaging of the lattice structure in particular if 2 to 6 nm small nanoparticles are involved. Therefore, FePt nanocrystals were investigated by reconstructing amplitude and phase of the scattered electron wave from a focal series of HRTEM images, which can produce delocalization free and direct images of the crystal structure [4]. The formation of 5-fold twinned structures of 3 to 7 nm face-centered cubic FePt nanocrystals is investigated that were grown from a colloidal solution [1]. The results are compared with abinitio density functional (DFT) calculations of FePt particles with a diameter of larger than 2 nm. Image simulations were performed with the Accelrys Cerius2 software package (Version 4.6). Good agreement between the ab-initio calculations and the experimental data is found.

A New Approach for Calculating Cohesive Energy of Solid Neon Based on the First Principles

2019 ◽  
Vol 807 ◽  
pp. 128-134
Author(s):  
Xing Rong Zheng
Keyword(s):  
First Principles ◽  
Cohesive Energy ◽  
High Pressures ◽  
New Combination ◽  
Rare Gas ◽  
Face Centered Cubic ◽  
New Approach ◽  
Molecular Systems ◽  
Ionic Systems ◽  
Face Centered

Based on the first principles and quantum mechanics, a new approach is put forward to calculate the cohesive energy of face-centered cubic solid neon, in which both the two-body and the total many-body interaction potentials are reasonably emphasized by a new combination formula. It shows that the new scheme is a simple and accurate tool to understand the high-pressure behaviors of solid neon, and it will be applied to calculate the compression curves of dense Helium, Argon, Krypton and Xenon at very high pressures. It is expected that this method can be applicable to all rare gas, including the gas, solid, and liquid phase regions, even of molecular systems, ionic systems.

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