Andriy Palasyuk

Turning Gold into “Diamond”: A Family of Hexagonal Diamond-Type Au-Frameworks Interconnected by Triangular Clusters in the Sr–Al–Au System

A new homologous series of intermetallic compounds containing three-dimensional (3-d) tetrahedral frameworks of gold atoms, akin to hexagonal diamond, have been discovered in four related Sr-Au-Al systems: (I) hexagonal SrAl3-xAu4+x (0.06(1) ≤ x ≤ 0.46(1), P62m, Z = 3, a = 8.633(1)-8.664(1) Å, c = 7.083(2)-7.107(1) Å); (II) orthorhombic SrAl2-yAu5+y (y ≤ 0.05(1); Pnma, Z = 4, a = 8.942(1) Å, b = 7.2320(4) Å, c = 9.918(1) Å); (III) Sr2Al2-zAu7+z (z = 0.32(2); C2/c, Z = 4, a = 14.956(4) Å, b = 8.564(2) Å, c = 8.682(1) Å, β = 123.86(1)°); and (IV) rhombohedral Sr2Al3-wAu6+w (w ≈ 0.18(1); R3c, Z = 6, a = 8.448(1) Å, c = 21.735(4) Å). These remarkable compounds were obtained by fusion of the pure elements and were characterized by X-ray diffraction and electronic structure calculations. Phase I shows a narrow phase width and adopts the Ba3Ag14.6Al6.4-type structure; phase IV is isostructural with Ba2Au6Zn3, whereas phases II and III represent new structure types. This novel series can be formulated as Srx[M3]1-xAu2, in which [M3] (= [Al3] or [Al2Au]) triangles replace some Sr atoms in the hexagonal prismatic-like cavities of the Au network. The [M3] triangles are either isolated or interconnected into zigzag chains or nets. According to tight-binding electronic structure calculations, the greatest overlap populations belong to the Al-Au bonds, whereas Au-Au interactions have a substantial nonbonding region surrounding the calculated Fermi levels. QTAIM analysis of the electron density reveals charge transfer from Sr to the Al-Au framework in all four systems. A study of chemical bonding by means of the electron-localizability indicator indicates two- and three-center interactions within the anionic Al-Au framework.

SrAu4In4 and Sr4Au9In13: Polar Intermetallic Structures with Cations in Augmented Hexagonal Prismatic Environments

The title compounds were synthesized via high-temperature reactions of the elements in welded Ta tubes and characterized by single-crystal X-ray diffraction analyses and band structure calculations. SrAu(3.76(2))In(4.24) crystallizes in the YCo5In3 structure type with two of eight network sites occupied by mixtures of Au and In: Pnma, Z = 4, a = 13.946(7), b = 4.458(2), c = 12.921(6) A. Its phase breadth appears to be small. Sr4Au9In 13 exhibits a new structure type, P_6 m2, Z = 1, a = 12.701(2), c = 4.4350(9) A. The Sr atoms in both compounds center hexagonal prisms of nominally alternating In and Au atoms and also have nine augmenting (outer) Au + In atoms around their waists so as to define 21-vertex Sr@Au9M4In8 (M = Au/In) and Sr@Au9In12 polyhedra, respectively. The relatively larger Sr content in the second phase also leads to condensation of some of the ideal building units into trefoil-like cages with edge-shared six-member rings. One overall driving force for the formation of these structures can be viewed as the need for each Sr cation to have as many close neighbors as possible in the more anionic Au-In network. The results also depend on the cation size as well as on the flexibility of the anionic network and an efficient intercluster condensation mode as all clusters are shared. Band structure calculations (LMTO-ASA) emphasize the greater strengths (overlap populations) of the Au-In bonds and confirm expectations that both compounds are metallic.

New alnico magnets fabricated from pre-alloyed gas atomization powder through diverse consolidation techniques

Recent concern for supply and price of rare earth (RE) metals has stimulated the search for alternative magnets [1]. Alnico is an attractive non-RE magnet alloy due to its excellent magnetic stability. However, the best energy product (BH)max of the magnets is only about 10 MGOe. A key to improving the magnetic properties is to enhance coercivity Hci by optimizing composition and microstructure [2]. While our efforts focus on how to improve the magnetic properties, new fabrication technologies of bulk alnico magnets are widely studied as well. In this study, fine spherical powder produced by gas atomization (GA) was consolidated through Hot Pressing (HP), Hot Isostatic Pressing (HIP), and Compression Molding and subsequently Sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were studied and discussed.

BaIrIn4 and Ba2Ir4In13: two In-rich polar intermetallic structures with different augmented prismatic environments about the cations.

The title phases were synthesized via high-temperature reactions of the elements in welded Ta tubes and characterized by single-crystal X-ray diffraction methods and band calculations. BaIrIn4 adopts the LaCoAl4-type structure: Pmma, Z = 2, a = 8.642(2), b = 4.396(1), and c = 7.906(2) A. Ba2Ir4In13 exhibits a new structure type: Cmc2(1), Z = 4, a = 4.4856(9), b = 29.052(6), and c = 13.687(3) A. BaIrIn4 is constructed from a single basic unit, a Ba-centered pentagonal prism of indium on which two adjacent and the opposed rectangular faces are capped by In and Ir, respectively. The three capping atoms are coplanar with Ba and represent the only augmentation of the pentagonal prism. The relatively large proportions of Ba:Ir, In, and of In:Ir lead to the condensation of homoatomic pentagonal prisms into zigzag chains through the sharing of the two uncapped faces. The cation proportion is much lower in Ba2Ir4In13, and Ba atoms are surrounded by a more anionic Ir/In network without any condensation between prisms. This and the greater Ir proportion lead to a network of formal augmented pentagonal Ba@Ir5In15 and hexagonal Ba@Ir7In15 prisms with overall 5-10-5 and 6-10-6 arrangements of parallel planar rings, respectively, although most Ir is not well bound to the prisms. The latter prism, with alternating Ir/In atoms in the basal faces, is novel for Ae-T-In phases (Ae = alkaline-earth metal, T = Co, Rh, Ir). Band structure calculation results (linear-muffin-tin-orbital method in the atomic sphere approximation) emphasize the greater overlap populations (approximately strengths) of the Ir-In bonds and confirm expectations that both compounds are metallic. The Ir 5d bands are narrower and lie higher in energy than those for Au in analogous phases.

Ce3-xMgxCo9: Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

We report on the synthesis of single crystalline and polycrystalline samples of Ce

Site-differentiated solid solution in (Na(1-x)Cu(x))2Ta4O11 and its electronic structure and optical properties.

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Advances in Characterization of Non-Rare-Earth Permanent Magnets: Exploring Commercial Alnico Grades 5–7 and 9

Mg

Synthesis and Structure of BaPtIn3 and BaTl0.63In3.33 Two Contrasting Examples of Preferential Site Occupation in BaAl4-Type Structures

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Crystal structures and magnetic properties of CeAu4Si2 and CeAu2Si2

Co

A Section Through the Compositional Triangle Pr-Co-I at 600 °C: Pr7CoI12 and Pr2Co2I†‡

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