scholarly journals High antisite defect concentrations in hard-sphere colloidal Laves phases

Soft Matter ◽  
2020 ◽  
Vol 16 (17) ◽  
pp. 4155-4161 ◽  
Author(s):  
Berend van der Meer ◽  
Frank Smallenburg ◽  
Marjolein Dijkstra ◽  
Laura Filion
Keyword(s):  
Small Particle ◽  
Hard Sphere ◽  
Large Particle ◽  
Antisite Defect ◽  
Laves Phase ◽  
High Concentration ◽  
Laves Phases ◽  
Antisite Defects

We show that the equilibrium Laves phase in binary hard-sphere mixtures contains an extraordinarily high concentration of antisite defects:  we find stable regions where up to 2% of the large-particle lattice sites are occupied by a small particle.

scholarly journals Laves Phase Formation in High Entropy Alloys

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1962
Author(s):  
Roman Ryltsev ◽  
Vasiliy Gaviko ◽  
Svetlana Estemirova ◽  
Evgenii Sterkhov ◽  
Lubov Cherepanova ◽  
...  
Keyword(s):  
Single Phase ◽  
Chemical Elements ◽  
Laves Phase ◽  
Structural Defects ◽  
Clear Understanding ◽  
High Entropy Alloys ◽  
High Concentration ◽  
Laves Phases ◽  
High Entropy ◽  
Chemical Complexity

One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x = 12x-VCrMoMnFe, 12x + Sc, 12x + Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x + Be alloy reveals a single-phase C14 structure with a very high concentration of structural defects and ultra-fine dendritic microstructure with an almost homogenous distribution of the constituted elements over the alloy matrix. The analysis of electrical and magnetic properties reveals that the Laves phases are Curie-Weiss paramagnets, which demonstrate metallic conduction; 7x and 12x alloys also reveal a pronounced Kondo-like anomaly. Analysis of experimental data as well as ab initio calculations suggest that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band.

scholarly journals Effect of Nd, Pr substitutional atoms on the magnetic and magnetostrictive properties in (Tb-Dy)(Fe-Co)2 Laves phases

2021 ◽  
Vol 2103 (1) ◽  
pp. 012196
Author(s):  
G A Politova ◽  
M A Ganin ◽  
A B Mikhailova ◽  
D A Morozov ◽  
K E Pankov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Magnetic Properties ◽  
Laves Phase ◽  
Type Structure ◽  
Partial Substitution ◽  
Laves Phases ◽  
Temperature Range ◽  
Homogenizing Annealing ◽  
Arc Melting ◽  
Magnetostrictive Materials

Abstract Polycrystalline TbxDy1-xR0.1Fe2-zCoz (R = Nd, Pr, x = 0.2, 0.3; z = 0, 1.3) cubic Laves phase alloys with MgCu2-type structure were prepared by arc melting followed by homogenizing annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. Compounds with high values of magnetostrictive susceptibility were found in the temperature range 150-300 K. Compounds with partial substitution of cobalt for iron demonstrate a change in the sign of anisotropic magnetostriction. This work continues the search for magnetostrictive materials with inexpensive neodymium and praseodymium.

Ternary transition metal gallides with TiNiSi, ZrBeSi and MgZn2-type structure

2019 ◽  
Vol 74 (3) ◽  
pp. 297-306 ◽  
Author(s):  
Lukas Heletta ◽  
Theresa Block ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Transition Metal ◽  
Powder Diffraction ◽  
Metallic Iron ◽  
Site Occupancy ◽  
Laves Phase ◽  
Structural Motif ◽  
Equiatomic Composition ◽  
Laves Phases ◽  
X Ray ◽  
Arc Melting

AbstractA series of ternary transition metal gallides around the equiatomic composition have been synthesized from the elements by arc-melting and subsequent annealing. The compounds crystallize with site occupancy variants of the hexagonal Laves phase MgZn2, with the hexagonal ZrBeSi or the orthorhombic TiNiSi type. All samples have been characterized on the basis of their lattice parameters, determined by X-ray powder diffraction (Guinier technique). The structures of NbCr1.58Ga0.42 and NbFe1.51Ga0.49 (MgZn2 type, P63/mmc), NbRhGa (ZrBeSi type, P63/mmc), and ScNiGa, ScPtGa and ScAuGa (TiNiSi type, Pnma) were refined from single crystal X-ray diffractometer data. The ScPtGa and ScAuGa crystals showed trilling formation. Mixed site occupancies were only observed in the Laves phases while all other crystals were well ordered. A striking structural motif of NbRhGa is the formation of niobium chains (264 pm Nb–Nb) along the c axis. Several gallides were magnetically characterized. They are Pauli paramagnets. The two crystallographically independent iron sites in the Laves phase TaFeGa could be distinguished in the 57Fe Mössbauer spectrum. The isomer shifts of 0.06(3) (Fe1) and –0.02(3) (Fe2) mm s−1 indicate metallic iron.

EL2 and gallium antisite defects in GaAs: Si

1989 ◽  
Vol 67 (4) ◽  
pp. 375-378 ◽  
Author(s):  
C. K. Teh ◽  
F. L. Weichman ◽  
C. C. Tin ◽  
P. A. Barnes
Keyword(s):  
Fourier Transform ◽  
Deep Level Transient Spectroscopy ◽  
Deep Level ◽  
Fourier Transform Infrared ◽  
Antisite Defect ◽  
Longitudinal Optic ◽  
Related Defect ◽  
Antisite Defects ◽  
Transient Spectroscopy ◽  
Silicon Doped

Photoluminescence (PL), Fourier-transform infrared (FTIR), and deep-level transient spectroscopy (DLTS) measurements have been made on various samples of silicon-doped liquid-encapsulated Czochralski-grown GaAs. All the samples show prominent PL peaks at 1.443 and 1.325 eV together with their longitudinal optic (LO) phonon peaks. The PL peak at 1.443 eV has been reported in the literature as being due to either GaAs or a boron-related defect. The FTIR results show the presence of BGa at 540.3 and 517.0 cm−1 and SiGa at 383.6 cm−1. We have observed that there is no correlation between the PL peak at 1.443 eV and BGa. Thus, we believe that this PL peak is related to the GaAs antisite defect. The presence of EL2 in the samples has been measured using DLTS. We have found that the intensity of the PL peak at 1.443 eV varies inversely with that of the EL2 peak. This relationship indirectly confirms that the 1.443 eV peak is due to the gallium antisite defect. The PL peak at 1.325 eV is significantly different from those reported in the literature for GaAs:Si. Measurements have also been made on samples of GaAs:Si annealed under different arsenic overpressures.

Microstructures and Wear Resistance of Al1.5CrFeNiTi0.5 and Al1.5CrFeNiTi0.5W0.5 High Entropy Alloy Coatings Manufactured by Laser Cladding

2019 ◽  
Vol 956 ◽  
pp. 154-159 ◽  
Author(s):  
Hui Liang ◽  
Bing Yang Gao ◽  
Ya Ning Li ◽  
Qiu Xin Nie ◽  
Zhi Qiang Cao
Keyword(s):  
Wear Resistance ◽  
Laser Cladding ◽  
Dendritic Structure ◽  
Laves Phase ◽  
High Entropy Alloy ◽  
Second Phase ◽  
Laves Phases ◽  
High Entropy ◽  
Two Phases ◽  
Bcc Phase

For the purpose of expanding the application scope of HEA coating manufactured on the surface modification of materials, in this work, the Al1.5CrFeNiTi0.5 and Al1.5CrFeNiTi0.5W0.5 HEA coatings were successfully manufactured using laser cladding method on SUS304. The microstructures and wear resistance of coatings are researched systematically. It is found that the W0 and W0.5 HEA coatings all exhibit the dendritic structure, which are constituted by BCC phases and Laves phases. With W element addition, the phase structures of W0.5 coating remain unchanged. W is dissolved in both two phases, but the solid solubility in Laves phase is higher compared to that in BCC phase. W0.5 coating with the highest microhardness of 848.34 HV, and the W0 coating with the microhardness of 811.45 HV, both of whose microhardness are four times more than that of SUS304 substrate. Among all samples, the W0.5 coating shows the optimal wear performance because of its larger content of hard second phase ( Laves phase).

Orientation Relationships in the System Nb-NbCr2

1997 ◽  
Vol 3 (S2) ◽  
pp. 707-708
Author(s):  
P. G. Kotula ◽  
K. C. Chen ◽  
D. J. Thoma ◽  
F. Chu ◽  
T. E. Mitchell
Keyword(s):  
Microstructural Characterization ◽  
Laves Phase ◽  
Orientation Relationships ◽  
Ion Milling ◽  
Two Phase ◽  
Laves Phases ◽  
Arc Melting ◽  
Transmission Electron ◽  
Structural Applications ◽  
Two Phases

Laves-phase intermetallics are of potential use as high-temperature structural materials. NbCr2-based C15-structured alloys are of particular interest for such applications. by themselves, Laves phases generally have poor ductility and fracture toughness at low temperatures. Two phase alloys (i.e., Laves phase and the ductile bcc phase) are considered more promising for structural applications. The orientation relationships between the two phases can contribute to the mechanical behavior of the material. In this study, observations of two different orientation relationships in a Nb-NbCr2 eutectic are discussed and compared with previous studies of the NbCr2 system, as well as the TiCr2 system.A Nb-NbCr2 eutectic alloy was prepared by arc-melting high-purity alloys followed by annealing at 1400°C for 100 h and then cooling at l°C/min. The complete details of the materials preparation have been given elsewhere. Specimens were prepared for observation in the transmission electron microscope (TEM) by cutting 3 mm discs with a coring saw, followed by dimpling and ion milling. Microstructural characterization was performed with a Philips CM30 TEM operating at 300 kV.

scholarly journals The Ice Water Paths of Small and Large Ice Species in Hurricanes Arthur (2014) and Irene (2011)

2017 ◽  
Vol 56 (5) ◽  
pp. 1383-1404 ◽  
Author(s):  
Evan A. Kalina ◽  
Sergey Y. Matrosov ◽  
Joseph J. Cione ◽  
Frank D. Marks ◽  
Jothiram Vivekanandan ◽  
...  
Keyword(s):  
Small Particle ◽  
Large Particle ◽  
Radar Data ◽  
Particle Identification ◽  
Convective Precipitation ◽  
Ratio Distribution ◽  
Identification Scheme ◽  
Ice Particles ◽  
Precipitation Type ◽  
Ice Water

AbstractDual-polarization scanning radar measurements, air temperature soundings, and a polarimetric radar-based particle identification scheme are used to generate maps and probability density functions (PDFs) of the ice water path (IWP) in Hurricanes Arthur (2014) and Irene (2011) at landfall. The IWP is separated into the contribution from small ice (i.e., ice crystals), termed small-particle IWP, and large ice (i.e., graupel and snow), termed large-particle IWP. Vertically profiling radar data from Hurricane Arthur suggest that the small ice particles detected by the scanning radar have fall velocities mostly greater than 0.25 m s−1 and that the particle identification scheme is capable of distinguishing between small and large ice particles in a mean sense. The IWP maps and PDFs reveal that the total and large-particle IWPs range up to 10 kg m−2, with the largest values confined to intense convective precipitation within the rainbands and eyewall. Small-particle IWP remains mostly <4 kg m−2, with the largest small-particle IWP values collocated with maxima in the total IWP. PDFs of the small-to-total IWP ratio have shapes that depend on the precipitation type (i.e., intense convective, stratiform, or weak-echo precipitation). The IWP ratio distribution is narrowest (broadest) in intense convective (weak echo) precipitation and peaks at a ratio of about 0.1 (0.3).

scholarly journals Assessment of the Compositional Influences on the Toughness of TiCr2-Base Laves Phase Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
Katherine C. Chen ◽  
Samuel M. Allen ◽  
James D. Livingston
Keyword(s):  
Crystal Structure ◽  
Single Phase ◽  
Laves Phase ◽  
Second Phase ◽  
Vickers Indentation ◽  
Toughening Mechanisms ◽  
Two Phase ◽  
Laves Phases ◽  
Effective Factors ◽  
Alloying Effects

ABSTRACTSystematic studies of alloys based on TiCr2 have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoichiometric TiCr2. Next, alloying effects were investigated with ternary Laves phases based on TiCr2. Different microstructures of two-phase alloys consisting of (Ti,Cr)-bcc+TiCr2 were also examined. Various toughening theories based on vacancies, site-substitutions, crystal structure (C14, C36, or C15) stabilization, and the presence of a second phase were evaluated. The most effective factors improving the toughness of TiCr2 were determined, and toughening mechanisms are suggested.

scholarly journals Deformation of C15 Laves Phase Alloys

1994 ◽  
Vol 364 ◽  
Author(s):  
F. Chu ◽  
D.P Pope
Keyword(s):  
Phase Diagram ◽  
Physical Properties ◽  
Mechanical Behavior ◽  
Laves Phase ◽  
Deformation Mechanisms ◽  
Laves Phases ◽  
Theoretical Approaches

AbstractDetails of the structure and previous work on the deformation of C15 Laves phases are reviewed. The phase diagram of the Hf-V-Nb system, some metallurgical and physical properties, mechanical behavior, and the deformation mechanisms of HfV2+Nb (C15 HfV2+Nb and V-rich bcc solution) are presented based on our previous work. Theoretical approaches to understanding the results of these studies are discussed.

scholarly journals A quantitative model of reticulo-rumen particle degradation and passage

1989 ◽  
Vol 62 (2) ◽  
pp. 465-479 ◽  
Author(s):  
A. Lirette ◽  
L. P. Milligan
Keyword(s):  
Small Particle ◽  
Large Particle ◽  
Dry Matter ◽  
Volatile Fatty Acids ◽  
Quantitative Description ◽  
Dry Weight ◽  
Quantitative Model ◽  
Total Flow ◽  
Low Concentrations ◽  
Large Particles

Labelled particles were prepared by mordanting low concentrations (0.1 or 5 g/kg dry matter) of chromium to neutral-detergent-extracted stems (1–2 mm or 10 mm in length) of bromegrass (Bromus inermis). These were used in the study of reticulo-rumen particle kinetics of four steers given bromegrass hay and from the results a quantitative model of particle digestion and passage was developed. At the 0.1 g Cr/kg concentration there was minimal interference with digestibility of the feedstuff. The ratio, dry weight of the reticulo-rumen large-particle pool (> 3.35 mm):small-particle pool (< 3.35 mm) was 2:1. It was derived from the model that volatile fatty acids (VFA) and carbon dioxide in the rumen were produced mainly from large particles, and that between 500 and 700 g/kg hay dry matter was digested in the reticulo-rumen. It was also derived from the model that a major portion, 200 (SE 110) g/kg, of the hay dry matter was rapidly solubilized and that the material leaving the reticulo-rumen was composed of small particles (500–840 g/kg), large particles (100–160 g/kg) and an unknown portion of soluble dry matter of hay (0-400 g/kg). Disappearance from the large-particle pool in the model involving the lowest Cr level was directed to formation of VFA and CO2(0.68 (SE 0.04) of total flow) to the small-particle pool (0.25 (SE 0.06) of total flow) and direct passage from the reticulo-rumen (0.07 (SE 0.002) of total flow). The disappearance from the small-particle pool was to VFA and CO2production and to the omasum accounting for 0.14 (SE 0.18) and 0.86 (SE 0.24) respectively, of the total flow. It was concluded that the low-level-mordanting technique in combination with appropriate sampling yielded a realistic quantitative description of forage breakdown and movement processes in the digestive tract of cattle.

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