Special Issue "Intermetallic"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: 31 January 2021.

Special Issue Editor

Prof. Dr. Andrei Vladimirovich Shevelkov
Website
Guest Editor
Department of Chemistry, Lomonosov Moscow State University, Moscow, Russian Federation
Interests: inorganic synthesis; intermetallic compounds; Zintl phases; clusters; crystal and electronic structure; thermoelectric and magnetocaloric materials; superconductors

Special Issue Information

Dear colleague,

Intermetallics are a vast class of compounds composed of metals and metalloids. According to the definition of Schulze, intermetallic compounds “are solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents”. So far, more than 21 thousand intermetallic compounds have been documented in the literature and data bases. They are very different in nature. Classical metallic alloys such as CuZn brass belong to the Hume-Rothery electron compounds and differ significantly from polar Zintl phases, exemplified by K8Sn44, with localized bonding. However, many intermetallics are found in between these two extremes exhibiting less-polar, mainly multicenter, bonding (e.g., Mn2Ga5 or RuAl2). The crystal structures of intermetallic compounds are also very different, ranging from the simple and symmetric rock salt and Cu3Au types to complex metallic alloys that feature thousands of atoms in their unit cells. Being extremely different in crystal and electronic structures, intermetallic compounds display a great variety of properties that justify their application. Many of them have been known for centuries, for instance the mechanical and acoustic properties of tin-rich bronze were known to the Chinese about four thousand years ago. The others have emerged in recent years, covering a broad scope of properties and applications, including superconductivity, complex magnetic phenomena, thermoelectric effect, and catalysis. In their discovery, we rely on elaborate synthetic methods as well as new and advanced tools for analyzing structure–property relations; and as our tools and methods progress, we begin to appreciate the growing complexity of intermetallic compounds that provides a vast field for emerging phenomena and materials. This makes the realm of intermetallic compounds an inexhaustible source of new compounds with new and better properties and advanced applications; it is a playground for generations of chemists, with high expectations of future remarkable discoveries.

Prof. Dr. Andrei Vladimirovich Shevelkov
Guest Editor

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Keywords

  • intermetallic compounds
  • crystal structure
  • chemical bonding
  • superconductivity
  • magnetic phenomenon
  • thermoelectric effect
  • catalysis

Published Papers (7 papers)

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Research

Open AccessArticle
Bismuth Polycations Revisited: Alternative Synthesis and Electronic Structure of Bi6Br7, and Bonding in Main-Group Polyatomic Ions from a Direct Space Perspective
Crystals 2020, 10(10), 940; https://doi.org/10.3390/cryst10100940 - 16 Oct 2020
Abstract
A bismuth subbromide, Bi6Br7, was synthesized in the form of single crystals using the reaction between Bi and Hg2Br2 in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, [...] Read more.
A bismuth subbromide, Bi6Br7, was synthesized in the form of single crystals using the reaction between Bi and Hg2Br2 in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, a = 15.4996(6) Å, b = 23.6435(7) Å, c = 9.0231(2) Å, Z = 8, R1 = 0.041, wRall = 0.087). Based on the diffraction data, the structure description was revised as containing Bi95+ cluster polycations and 1[Bi3Br145−] ladder-like anions. DFT calculations of band structure showed the compound to be a narrow-gap semiconductor with a band gap of ca. 1.3 eV, with the nature of the compound as ionic salt confirmed by charge density analysis. Direct-space bonding analysis based on the ELF topology and QTAIM partitioning, performed for all known homoatomic bismuth polycations, as well as isoelectronic main-group metal ions, shows patterns of localized pairwise and three-center bonding forming the frameworks of the clusters. In addition to obtaining new data, the use of highly augmented basis sets allowed us to revise and amend several previously made conclusions regarding bonding in such species. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
Revealing the Bonding Nature in an ALnZnTe3-Type Alkaline-Metal (A) Lanthanide (Ln) Zinc Telluride by Means of Experimental and Quantum-Chemical Techniques
Crystals 2020, 10(10), 916; https://doi.org/10.3390/cryst10100916 - 10 Oct 2020
Abstract
Tellurides have attracted an enormous interest in the quest for materials addressing future challenges, because many of them are at the cutting edge of basic research and technologies due to their remarkable chemical and physical properties. The key to the tailored design of [...] Read more.
Tellurides have attracted an enormous interest in the quest for materials addressing future challenges, because many of them are at the cutting edge of basic research and technologies due to their remarkable chemical and physical properties. The key to the tailored design of tellurides and their properties is a thorough understanding of their electronic structures including the bonding nature. While a unique type of bonding has been recently identified for post-transition-metal tellurides, the electronic structures of tellurides containing early and late-transition-metals have been typically understood by applying the Zintl−Klemm concept; yet, does the aforementioned formalism actually help us in understanding the electronic structures and bonding nature in such tellurides? To answer this question, we prototypically examined the electronic structure for an alkaline metal lanthanide zinc telluride, i.e., RbDyZnTe3, by means of first-principles-based techniques. In this context, the crystal structures of RbLnZnTe3 (Ln = Gd, Tb, Dy), which were obtained from high-temperature solid-state syntheses, were also determined for the first time by employing X-ray diffraction techniques. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
First Principles Density Functional Theory Prediction of the Crystal Structure and the Elastic Properties of Mo2ZrB2 and Mo2HfB2
Crystals 2020, 10(10), 865; https://doi.org/10.3390/cryst10100865 - 24 Sep 2020
Abstract
The Molybdenum rich ternary alloys Mo-M-B (M = Zr, Hf) contain, next to the Mo solid solution (bcc Mo with small amounts of Zr or Hf as substitutional atoms), the binary borides Mo2B, MB and MB2. Recently, it was [...] Read more.
The Molybdenum rich ternary alloys Mo-M-B (M = Zr, Hf) contain, next to the Mo solid solution (bcc Mo with small amounts of Zr or Hf as substitutional atoms), the binary borides Mo2B, MB and MB2. Recently, it was found that there is also ternary Mo2MB2, but the crystal structure and further properties are currently unknown. Density functional theory (DFT) calculations were used not only to predict the crystal structure of the Mo2MB2 phases, but also to estimate the isotropic and anisotropic elastic properties like bulk, shear and Young’s modulus, as well as the Vickers hardness of these new borides. Several known crystal structures that fulfill the criterion of the chemical composition were investigated, and the AlMn2B2 type structure seems to be the most stable crystal structure for Mo2HfB2 and Mo2ZrB2 as there are no signs of electronic or dynamic instability. Regarding the elastic properties, it was found that Mo2HfB2 shows higher elastic moduli and is less elastically anisotropic than Mo2ZrB2. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
Nowotny Chimney Ladder Phases with Group 5 Metals: Crystal and Electronic Structure and Relations to the CrSi2 Structure Type
Crystals 2020, 10(8), 670; https://doi.org/10.3390/cryst10080670 - 03 Aug 2020
Abstract
Nowotny chimney ladder (NCL) phases are intermetallic compounds formed by transition metals and metals of groups 13 and 14. This family can be expanded by combining two p-elements from different groups with those transition metals, for which the corresponding binary NCL phases [...] Read more.
Nowotny chimney ladder (NCL) phases are intermetallic compounds formed by transition metals and metals of groups 13 and 14. This family can be expanded by combining two p-elements from different groups with those transition metals, for which the corresponding binary NCL phases are unknown. In this paper, we present three new compounds in the V-Al-Ge, Nb-Al-Ge, and Nb-Ga-Ge systems related to the TiSi2 structure type (Sp. Gr. Fddd) obtained with the standard ampule technique. The crystal structures of the new compounds were determined using synchrotron powder X-ray diffraction data. A transition to the CrSi2 structure type was detected upon changing the composition from VAl0.72(2)Ge1.28(2) to VAl1.534(3)Ge0.466(3). According to the 18–n rule, all the compounds are metallic conductors, which was supported by the electronic structure calculations. It was shown that the expected energy gap located above the Fermi level in the vanadium-based NCL compound collapsed into a pseudogap upon the replacement of V by Nb. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
Growth and Magnetism of MnxGe1−x Heteroepitaxial Quantum Dots Grown on Si Wafer by Molecular Beam Epitaxy
Crystals 2020, 10(6), 534; https://doi.org/10.3390/cryst10060534 - 23 Jun 2020
Abstract
Self-assembled MnGe quantum dots (QDs) were grown on Si (001) substrates using molecular beam epitaxy with different growth temperatures and Ge deposition thicknesses to explore the interaction among Mn doping, Ge deposition, the formation of intermetallics, and the ferromagnetism of QDs. With the [...] Read more.
Self-assembled MnGe quantum dots (QDs) were grown on Si (001) substrates using molecular beam epitaxy with different growth temperatures and Ge deposition thicknesses to explore the interaction among Mn doping, Ge deposition, the formation of intermetallics, and the ferromagnetism of QDs. With the introduction of Mn atoms, the QDs become large and the density significantly decreases due to the improvement in the surface migration ability of Ge atoms. The growth temperature is one of the most important factors deciding whether intermetallic phases form between Mn and Ge. We found that Mn atoms can segregate from the Ge matrix when the growth temperature exceeds 550 °C, and the strongest ferromagnetism of QDs occurs at a growth temperature of 450 °C. As the Ge deposition thickness increases, the morphology of QDs changes and the ferromagnetic properties decrease gradually. The results clearly indicate the morphological evolution of MnGe QDs and the formation conditions of intermetallics between Mn and Ge, such as Mn5Ge3 and Mn11Ge8. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
Ternary Aluminides of a New Homologous Series—CePt2Al2 and CePt3Al3: Crystal Structures and Thermal Properties
Crystals 2020, 10(6), 465; https://doi.org/10.3390/cryst10060465 - 01 Jun 2020
Cited by 1
Abstract
In the process of studying the Ce–Pt–Al system, we identified CePt2Al2 and CePt3Al3, two new ternary intermetallic compounds. CePt2Al2 aluminide undergoes a structural phase transition from a low-temperature orthorhombic modification (of its own [...] Read more.
In the process of studying the Ce–Pt–Al system, we identified CePt2Al2 and CePt3Al3, two new ternary intermetallic compounds. CePt2Al2 aluminide undergoes a structural phase transition from a low-temperature orthorhombic modification (of its own structure type, Cmme, a = 5.84138(2) Å, b = 6.39099(3) Å, c = 10.11611(5) Å) to a high-temperature tetragonal modification (CaBe2Ge2 type, P4/nmm, a = 4.3637(9) Å, c = 10.0925(14) Å) at 280(1) °C. CePt3Al3 crystallizes with a new type of structure (Cmme, a = 6.36548(6) Å, b = 5.78301(6) Å, c = 13.36245(19) Å) built of structural units of low-temperature orthorhombic CePt2Al2-type and CsCl-type. Full article
(This article belongs to the Special Issue Intermetallic)
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Open AccessArticle
Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)
Crystals 2020, 10(4), 298; https://doi.org/10.3390/cryst10040298 - 13 Apr 2020
Abstract
Exploratory studies in the systems Rb–Ga–Sn and Cs–Ga–Sn yielded the cubic type-I clathrates with refined compositions Rb8GaxSn46−x and Cs8GaxSn46−x (6.9 < x < 7.5). Nearly single-phase materials with good crystallinity were obtained [...] Read more.
Exploratory studies in the systems Rb–Ga–Sn and Cs–Ga–Sn yielded the cubic type-I clathrates with refined compositions Rb8GaxSn46−x and Cs8GaxSn46−x (6.9 < x < 7.5). Nearly single-phase materials with good crystallinity were obtained from stoichiometric reactions of the elements. The structures were characterized by means of single-crystal X-ray diffraction methods. Both Rb8GaxSn46−x and Cs8GaxSn46−x represents cases, where a Group 13 element randomly substitutes a Group 14 element in the structure. The extent of Ga/Sn mixing is apparently governed by the drive of the system to achieve an optimal valence electron count, and hence, Rb8GaxSn46−x and Cs8GaxSn46−x (x ≈ 8) can be regarded as Zintl phases. This notion is supported by structure refinements on a multitude of single-crystal X-ray diffraction data, which also confirm that both types of cages in the cubic type-I structure are fully occupied by Rb and Cs atoms. The open-framework, comprised of 46 nodes per formula unit, adapts to the incorporation of nearly eight Ga atoms within the matrix of Sn, whereby small, short-range distortions result. The exact nature of these effects is still unclear, as so far, the structural variations could only be modeled as both positional and occupational disorder at one of three framework sites. Since vacancies in the structures of the binary type-I clathrates A8Sn46−xx (A = Rb, Cs; ☐ = missing Sn atom) are also known to cause local distortions, the latter were also synthesized with the same protocols used for the synthesis of A8GaxSn46−x and structurally re-analyzed. The results from the latter studies confirm that homogeneity issues abound, and that the final structures/compositions are an intricate function of the experimental conditions. Full article
(This article belongs to the Special Issue Intermetallic)
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