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21 pages, 5349 KiB

Open AccessArticle

High-Throughput Preparation and Characterization of ZrMoTaW Refractory Multi-Principal Element Alloy Film

by Qiannan Wang, Hongwang Yang, Xiaojiao Zuo, Yinxiao Wang and Jiahao Yao

Materials 2022, 15(23), 8546; https://doi.org/10.3390/ma15238546 - 30 Nov 2022

Cited by 3 | Viewed by 1720

In this work, high-throughput screening technology is applied to four-member refractory multi-principal element alloys (RMPEAs) films with high W content. The exploration of refractory metals such as W is strictly limited by the high melting temperature in this work; a multi-gradient deposition method [...] Read more.

In this work, high-throughput screening technology is applied to four-member refractory multi-principal element alloys (RMPEAs) films with high W content. The exploration of refractory metals such as W is strictly limited by the high melting temperature in this work; a multi-gradient deposition method was introduced to overcome this obstacle. By adjusting the power and distance from the target to the sample, component Zr₁₁Mo₁₁Ta₂₅W₅₃ with the best hardening performance was successfully obtained. The uniformity of the material library was analyzed from the perspectives of phase structure and micromorphology. With the help of Hume-Rothery theory and XRD analysis, it is shown that the film has a stable bcc structure. It is believed that film uniformity, nanoscale size, preferential orientation, surface roughness, and solution mechanism are the pivotal factors to improve hardness performance, especially for high W components. The hardness and modulus of elasticity can reach 20 GPa and 300 GPa, respectively, and the H/Er and H³/Er² values are 0.067 and 0.065, showing the best wear resistance in many samples. Full article

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15 pages, 2649 KiB

Open AccessArticle

The Polyol Process and the Synthesis of ζ Intermetallic Compound Ag₅Sn_0.9

by Roland Mahayri, Mohammed Ali Bousnina, Silvana Mercone, Ky-Lim Tan, Jean-Michel Morelle, Frédéric Schoenstein and Noureddine Jouini

Materials 2022, 15(22), 8276; https://doi.org/10.3390/ma15228276 - 21 Nov 2022

Cited by 1 | Viewed by 2838

Abstract

The present work concerns the intermetallic compound (IMC) existing in the Ag–Sn system and its potential use in electronics as attachment materials allowing the adhesion of the chip to the substrate forming the power module. First, we present the synthesis protocol in polyol [...] Read more.

The present work concerns the intermetallic compound (IMC) existing in the Ag–Sn system and its potential use in electronics as attachment materials allowing the adhesion of the chip to the substrate forming the power module. First, we present the synthesis protocol in polyol medium of a compound with the chemical formula Ag₅Sn_0.9 belonging to the solid solution of composition located between 9 and 16 at.% Sn, known as solid solution ζ (or ζ-Ag₄Sn). This phase corresponds to the peritectic invariant point at 724 °C. Differential thermal analysis and X-ray dispersive analysis confirm the single-phased (monocrystalline) nature of the Ag₅Sn_0.9 powder issued after synthesis. Scanning electron microscopy shows that Ag₅Sn_0.9 particles are spherical, and range in submicronic size of around 0.18 μm. X-ray diffraction analysis reveals that the ζ phase mostly exists under the two allotropic varieties (orthorhombic symmetry and hexagonal symmetry) with however a slight excess of the hexagonal variety (60% for the hexagonal variety and 40% for the orthorhombic variety). The lattice parameters resulting from this study for the two allotropic varieties are in good agreement with the Hume-Rothery rules. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Preparation, Properties and Applications)

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11 pages, 1387 KiB

Open AccessArticle

On the Sintering Behavior of Nb₂O₅ and Ta₂O₅ Mixed Oxide Powders

by Maureen P. Chorney, Kunal Mondal, Jerome P. Downey and Prabhat K. Tripathy

Materials 2022, 15(14), 5036; https://doi.org/10.3390/ma15145036 - 20 Jul 2022

Cited by 2 | Viewed by 2319

Abstract

A mixed oxide system consisting of Nb₂O₅ and Ta₂O_5, was subjected to annealing in air/hydrogen up to 950 °C for 1–4 h to study its sintering behavior. The thermogravimetric–differential scanning calorimetry (TGA–DSC) thermograms indicated the formation of [...] Read more.

A mixed oxide system consisting of Nb₂O₅ and Ta₂O_5, was subjected to annealing in air/hydrogen up to 950 °C for 1–4 h to study its sintering behavior. The thermogravimetric–differential scanning calorimetry (TGA–DSC) thermograms indicated the formation of multiple endothermic peaks at temperatures higher than 925 °C. Subsequently, a 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) pellet resulted in good sintering behavior at both 900 and 950 °C. The scanning electron microscope (SEM) images corroborated these observations with necking and particle coarsening. The sintered pellets contained a 20.4 and 20.8% mixed oxide (Nb₄Ta₂O₁₅) phase, along with Ta₂O₅ and Nb₂O₅, at both 900 and 950 °C, indicating the possibility of the formation of a solid solution phase. In situ high-temperature X-ray diffraction (XRD) scans also confirmed the formation of the ternary oxide phase at 6 and 19.8% at 890 and 950 °C, respectively. The Hume–Rothery rules could explain the good sintering behavior of the Ta₂O₅ and Nb₂O₅ mixed oxides. An oxide composition of 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) and a sintering temperature of 950 °C appeared adequate for fabricating well-sintered oxide precursors for subsequent electrochemical polarization studies in fused salts. Full article

(This article belongs to the Special Issue Powder Metallurgy: Materials and Processing)

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17 pages, 15291 KiB

Open AccessArticle

Design and Production of a New FeCoNiCrAlCu High-Entropy Alloy: Influence of Powder Production Method on Sintering

by Eduardo Reverte, Monique Calvo-Dahlborg, Ulf Dahlborg, Monica Campos, Paula Alvaredo, Pablo Martin-Rodriguez, Elena Gordo and Juan Cornide

Materials 2021, 14(15), 4342; https://doi.org/10.3390/ma14154342 - 3 Aug 2021

Cited by 3 | Viewed by 3132

Abstract

The structure of FeCoNiCrAl1.8Cu0.5 high-entropy alloys (HEA) obtained by two different routes has been studied. The selection of the composition has followed the Hume–Rothery approach in terms of number of itinerant electrons (e/a) and average atomic radius to control the formation of specific [...] Read more.

The structure of FeCoNiCrAl1.8Cu0.5 high-entropy alloys (HEA) obtained by two different routes has been studied. The selection of the composition has followed the Hume–Rothery approach in terms of number of itinerant electrons (e/a) and average atomic radius to control the formation of specific phases. The alloys were obtained either from a mixture of elemental powders or from gas-atomised powders, being consolidated in both cases by uniaxial pressing and vacuum sintering at temperatures of 1200 °C and 1300 °C. The characterization performed in the sintered samples from both types of powder includes scanning electron microscopy, X-ray diffraction, differential thermal analysis, and density measurements. It was found that the powder production techniques give similar phases content. However, the sintering at 1300 °C destroys the achieved phase stability of the samples. The phases identified by all techniques and confirmed by Thermo-Calc calculations are the following: a major Co-Ni-Al-rich (P1) BCC phase, which stays stable after 1300 °C sintering and homogenising TT treatments; a complex Cr-Fe-rich (P2) B2 type phase, which transforms into a sigma phase after the 1300 °C sintering and homogenising TT treatments; and a very minor Al-Cu-rich (P3) FCC phase, which also transforms into Domain II and Domain III phases during the heating at 1300 °C and homogenising TT treatments. Full article

(This article belongs to the Special Issue Materials Sintering)

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20 pages, 3714 KiB

Open AccessArticle

Phase Formation of Mg-Zn-Gd Alloys on the Mg-rich Corner

by Lan Luo, Yong Liu and Meng Duan

Materials 2018, 11(8), 1351; https://doi.org/10.3390/ma11081351 - 3 Aug 2018

Cited by 15 | Viewed by 5088

Abstract

The phase constitutions of as-cast magnesium (Mg)-Zn-Gd alloys (Zn/Gd = 0.25~60, Zn 0~10 at.%, Gd 0~2 at.%, 48 samples) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-Zn-Gd phase diagram focused on the Mg-rich corner [...] Read more.

The phase constitutions of as-cast magnesium (Mg)-Zn-Gd alloys (Zn/Gd = 0.25~60, Zn 0~10 at.%, Gd 0~2 at.%, 48 samples) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-Zn-Gd phase diagram focused on the Mg-rich corner (with up to 20 at.% Zn, 10 at.% Gd) has been set up. Five regions can be classified as follows: (I) α-Mg+W-phase+(binary compounds), (II) α-Mg+W-phase+I-phase(+binary compounds), (III) α-Mg+I-phase(+binary compounds), (IV) α-Mg+binary compounds, and (V) α-Mg. The phase diagram has been verified by solidification behaviors observation using differential thermal analysis (DTA). Moreover, the structures of I-phase and W-phase in the alloy were explored in details. In terms of the Hume-Rothery rules, I-phase is confirmed as FK-type quasicrystalline with a chemical stoichiometry as Mg_30±1Zn₆₂Gd_8±1 (at.%). The composition and lattice parameter a W-phase (fcc structure,

m \bar{3} m

) are affected by the composition of Mg-Zn-Gd alloys, especially by the Zn/Gd ratio of alloys. This work would be instructive for the design of Mg-Zn-Gd alloys to obtain the phase components, and then selected the strengthening ways, which could adjust its mechanical properties. Full article

(This article belongs to the Section Advanced Materials Characterization)

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23 pages, 7084 KiB

Open AccessReview

Revealing Tendencies in the Electronic Structures of Polar Intermetallic Compounds

by Fabian C. Gladisch and Simon Steinberg

Crystals 2018, 8(2), 80; https://doi.org/10.3390/cryst8020080 - 2 Feb 2018

Cited by 35 | Viewed by 6685

Abstract

The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by [...] Read more.

The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by Zintl and Hume–Rothery help to understand and forecast the bonding motifs in several intermetallic compounds, there is an emerging group of compounds dubbed as polar intermetallic phases whose electronic structures cannot be categorized by the aforementioned conceptions. These polar intermetallic compounds can be divided into two categories based on the building units in their crystal structures and the expected charge distributions between their components. On the one hand, there are polar intermetallic compounds composed of polycationic clusters surrounded by anionic ligands, while, on the other hand, the crystal structures of other polar intermetallic compounds comprise polyanionic units combined with monoatomic cations. In this review, we present the quantum chemical techniques to gain access to the electronic structures of polar intermetallic compounds, evaluate certain trends from a survey of the electronic structures of diverse polar intermetallic compounds, and show options based on quantum chemical approaches to predict the properties of such materials. Full article

(This article belongs to the Special Issue Functional Multi-Scale Crystals)

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10 pages, 1896 KiB

Open AccessArticle

Structurally Complex Frank–Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability

by Valentina F. Degtyareva and Natalia S. Afonikova

Crystals 2017, 7(12), 359; https://doi.org/10.3390/cryst7120359 - 4 Dec 2017

Cited by 3 | Viewed by 4817

Abstract

Metal crystals with tetrahedral packing are known as Frank–Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number [...] Read more.

Metal crystals with tetrahedral packing are known as Frank–Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere–Brillouin zone interaction model for several typical examples: Cu₄Cd₃, Mg₂Al₃ with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146–168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS) is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices. Full article

(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)

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13 pages, 1519 KiB

Open AccessArticle

Simple Metal and Binary Alloy Phases Based on the fcc Structure: Electronic Origin of Distortions, Superlattices and Vacancies

by Valentina F. Degtyareva and Nataliya S. Afonikova

Crystals 2017, 7(2), 34; https://doi.org/10.3390/cryst7020034 - 28 Jan 2017

Cited by 10 | Viewed by 7915

Abstract

Crystal structures of simple metals and binary alloy phases based on the face-centered cubic (fcc) structure are analyzed within the model of Fermi sphere–Brillouin zone interactions to understand the stability of the original cubic structure and derivative structures with distortions, superlattices [...] Read more.

Crystal structures of simple metals and binary alloy phases based on the face-centered cubic (fcc) structure are analyzed within the model of Fermi sphere–Brillouin zone interactions to understand the stability of the original cubic structure and derivative structures with distortions, superlattices and vacancies. Examination of the Brillouin–Jones configuration in relation to the nearly-free electron Fermi sphere for several representative phases reveals significance of the electron energy contribution to the phase stability. Representation of complex structures in the reciprocal space clarifies their relationship to the basic cubic cell. Full article

(This article belongs to the Section Crystal Engineering)

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13 pages, 791 KiB

Open AccessArticle

Bonding Schemes for Polar Intermetallics through Molecular Orbital Models: Ca-Supported Pt–Pt Bonds in Ca₁₀Pt₇Si₃

by Daniel C. Fredrickson, Isa Doverbratt, Siméon Ponou and Sven Lidin

Crystals 2013, 3(3), 504-516; https://doi.org/10.3390/cryst3030504 - 3 Sep 2013

Cited by 11 | Viewed by 8753

Abstract

Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca₁₀Pt [...] Read more.

Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca₁₀Pt₇Si₃, whose large Ca content offers the potential for negative formal oxidation states on the Pt. The structure can be divided into a sublattice of Ca cations and a Pt–Si polyanionic network built from Pt₇Si₃ trefoil units linked through Pt–Pt contacts of 3.14 Å. DFT-calibrated Hückel models reveal that the compound adheres well to a Zintl-like electron counting scheme, in which the Pt–Si and Pt–Pt contacts are equated with two-center two-electron bonds. The experimental electron count is in excess of that predicted by 2%, a discrepancy which is attributed to the electron transfer from the Ca to the Pt–Si network being incomplete. For the Pt–Pt contacts, the occupancy of the bonding orbitals is dependent on the participation of the surrounding Ca atoms in bridging interactions. This use of multi-center interactions isolobal to classical two-center two-electron bonds may illustrate one path by which the bonds delocalize as one moves from the Zintl phases toward the Hume-Rothery domain. Full article

(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)

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12 pages, 364 KiB

Open AccessArticle

Electronic Origin of the Orthorhombic Cmca Structure in Compressed Elements and Binary Alloys

by Valentina F. Degtyareva

Crystals 2013, 3(3), 419-430; https://doi.org/10.3390/cryst3030419 - 19 Jul 2013

Cited by 10 | Viewed by 9771

Abstract

Formation of the complex structure with 16 atoms in the orthorhombic cell, space group Cmca (Pearson symbol oC16), was experimentally found under high pressure in the alkali elements (K, Rb, Cs) and polyvalent elements of groups IV (Si, Ge) and V (Bi). [...] Read more.

Formation of the complex structure with 16 atoms in the orthorhombic cell, space group Cmca (Pearson symbol oC16), was experimentally found under high pressure in the alkali elements (K, Rb, Cs) and polyvalent elements of groups IV (Si, Ge) and V (Bi). Intermetallic phases with this structure form under pressure in binary Bi-based alloys (Bi-Sn, Bi-In, Bi-Pb). Stability of the Cmca-oC16 structure is analyzed within the nearly free-electron model in the frame of Fermi sphere-Brillouin zone interaction. A Brillouin-Jones zone formed by a group of strong diffraction reflections close to the Fermi sphere is the reason for the reduction of crystal energy and stabilization of the structure. This zone corresponds well to the four valence electrons in Si and Ge, and leads to assume an spd-hybridization for Bi. To explain the stabilization of this structure within the same model in alkali metals, that are monovalents at ambient conditions, a possibility of an overlap of the core, and valence band electrons at strong compression, is considered. The assumption of the increase in the number of valence electrons helps to understand sequences of complex structures in compressed alkali elements and unusual changes in their physical properties, such as electrical resistance and superconductivity. Full article

(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)

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