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An1.33T4Al8Si2 (An = Ce, Th, U, Np; T = Ni, Co) were synthesized in metal flux reactions carried out in aluminum/gallium melts. In previous work, U1.33T4Al8Si2 (T = Co, Ni) analogues were formed by arc-melting U:T:Si and reacting this mixture in Al/Ga flux. However, in the current work, all compounds were synthesized by using AnO2 reactants, taking advantage of the ability of the aluminum in the flux to act as both solvent and reducing agent. While reactions with T = Co yielded hexagonal Gd1.33Fe4Si10-type quaternary phases for all An, reactions with T = Ni produced these compounds only with An = U and Np. For reactions with An = Ce and Th, the reactions led instead to the formation of AnNi3-xSixAl4-yGay phases, with the tetragonal KCu3S4 structure type. Attempts to synthesize plutonium analogues Pu1.33T4Al8Si2 were also unsuccessful, producing the previously reported PuCoGa5 and Pu2Ni5Si6 instead. Magnetic data collected on the neptunium analogues Np1.33T4Al8Si2 (T = Ni, Co) show antiferromagnetic coupling at low temperatures and indicate a tetravalent state for the Np ions.

Reactions of cerium and nickel in excess molten gallium were monitored by neutron diffraction during heating and cooling. The formation of binary intermediates CeGa

Reactions of iron and carbon in a Pr/Ni eutectic flux have yielded three new Pr/Fe/C carbometalate compounds. Pr14Fe6C13 forms in tetragonal space group P42/mnm; Pr26Fe19C29 forms in orthorhombic s...

Reactions of tetrels (Tt = Si, Ge, Sn) with divalent alkaline earth or rare earth metals (A = Ca, Sr, Ba, Yb, Eu) in magnesium-rich melts produce a large family of structurally related metal tetrel...

Reactions of boron, tellurium, and either iron or manganese in a praseodymium-nickel flux led to the production of Pr21M16Te6B30 (M = Fe or Mn) with a novel structure type that features M16B30 clusters surrounded by a Pr/Te framework. Due to disorder in the orientation of the transition metal boride clusters, these phases initially appear to form in the cubic space group Pm3m. However, analysis of site occupancy, bond lengths, and local structure in the M16B30 sublattice indicates the local symmetry is P43m. This space group symmetry is supported by transmission electron microscopy studies including selected area electron diffraction (SAED) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), which indicate ordered regions. The M16B30 cluster twinning domain that could be as small as nanometer size inside a single crystal results in the misleading Pm3m symmetry. Electronic structure calculations indicate the Pr21M16Te6B30 phases are metals. Magnetic susceptibility measurements show that both the praseodymium and the transition metal have magnetic moments in these compounds. Pr21Mn16Te6B30 exhibits antiferromagnetic ordering at TN = 15 K, and Pr21Fe16Te6B30 undergoes a likely ferrimagnetic transition at TC = 23 K.

An

MgNi2Bi4 was grown from the reaction of magnesium and nickel in excess bismuth flux. It forms as large, malleable crystals with a new structure type in orthorhombic space group Cmcm. The structure contains a building block common to Ni-Bi binary phases-nickel zigzag chains running along one direction and surrounded by bismuth. Magnetic susceptibility and transport measurements indicate that the compound is metallic; this is supported by calculations of density of states. Crystal orbital Hamilton population analyses indicate that Ni-Bi interactions are the strongest bonding interactions in the structure, whereas Bi-Bi bonding between the layers is negligible, making MgNi2Bi4 a potential two-dimensional material.

Two new quaternary analogs of the Gd1+xFe4Si10-y structure type were grown from the reaction of uranium, silicon, and a transition metal (nickel or cobalt) in an excess of aluminum/gallium flux. The use of a mixed flux was found to be necessary for the formation of U1.33T4Al8Si2 (T = Ni, Co). Single crystal X-ray diffraction data shows the presence of disordered U/Si layers that are characteristic of this structure type; precession photographs indicate partial formation of a superstructure and stacking disorder along the c-axis. This disorder may be the cause of the spin glass behavior that is particularly evident in the nickel analog, which exhibits a spin freezing transition at TF = 7 K. These compounds are resistant to chemical attack and oxidation and may be potential waste forms.

Molten mixtures of ytterbium and lithium metals can be used as fluxes for the synthesis of metal hydrides. Reactions of indium and lithium hydride in Yb/Li flux produce Yb~51In13H27 (cubic, Im-3; a = 16.218(6) A, Z = 2). Yb~51In13H27 is an analog of previously reported Ca54In13H27 which was grown from Ca/Li flux. The compound features In@Yb12@H20@Yb30 Bergman-like clusters at the corners and body centers of the cubic lattice. The clusters are connected by a hydride site and disordered ytterbium sites. Magnetic susceptibility measurements indicate the ytterbium is divalent; the compound shows diamagnetic behavior with a Curie tail at lower temperatures attributed to impurities such as traces of Yb3+ that form on crystal surfaces due to slight oxidation.

La15(FeC6)4H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La3.67FeC6, a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La15(FeC6)4H is metallic and is stabilized by the incorporation of hydride anions.

High entropy alloys (HEA) are an unusual class of materials where mixtures of elements are stochastically arrayed on a simple crystalline lattice. These systems exhibit remarkable functionality, often along several distinct axes: e.g., the examples [TaNb]1-x(TiZrHf)x are high strength and damage resistant refractory metals that also exhibit superconductivity with large upper critical fields. Here we report the discovery of an f-electron containing HEA, [TaNb]0.31(TiUHf)0.69, which is the first to include an actinide ion. Similar to the Zr-analogue, this material crystallizes in a body-centered cubic lattice with the lattice constant a = 3.41(1) Å and exhibits phonon mediated superconductivity with a transition temperatures Tc ≈ 3.2 K and upper critical fields Hc2 ≈ 6.4 T. These results expand this class of materials to include actinide elements, shows that superconductivity is robust in this sub-group, and opens the path towards leveraging HEAs as functional waste forms for a variety of radioisotopes.

Reactions of boron, tellurium, and either iron or manganese in a praseodymium-nickel flux led to the production of Pr

Reactions of silicon, carbon, and iron in a low-melting flux mixture of praseodymium and nickel produced two competing intermetallic compounds. Pr62Fe21Si16C32 has a new structure type in tetragonal space group P4/ mmm ( a = 15.584(2) A, c = 11.330(1) A, Z = 1) that features trigonal planar FeC3 units that share corners to form a framework of cylindrical channels encompassing a network of silicon-centered praseodymium clusters. Slight variation of reactant ratio and heating profile produced Pr21Fe8Si7C12 instead; this compound has the previously reported cubic La21Fe8Sn7C12 structure type. Identical Pr/Si clusters and FeC3 subunit motifs are found in both structure types. In addition to reactant ratio and heating profile, size effects play a role in determining which structure forms. Replacing silicon with smaller phosphorus atoms produces only the tetragonal structure; replacement with larger elements (M = Ge, Sn) yields only cubic Pr21Fe8M7C12. Magnetic susceptibility measurements on single crystals of Pr62Fe21Si16C32 indicate antiferromagnetic ordering of the Pr moments below 17 K and no magnetic moment on iron atoms. The behavior of Pr21Fe8Si7C12 is more complex, revealing magnetic contributions from both Pr and Fe atoms and possible spin frustration.

Three new metal silicides were grown as competing products from reactions of silicon with barium and ytterbium in Mg/Al flux; the dominant product is determined by the heating profile as well as by the reactant ratio. The compounds Ba2Yb0.88Mg11.12Si7, Ba5Yb2.26Mg16.73Si12, and Ba20Yb4.7Mg61.3Si43 all exhibit hexagonal crystal structures that are analogous to those of ternary metal phosphides (Zr2Ni12P7, Ho5Ni19P12, and Ho20Ni66P43, respectively). The structures feature building blocks composed of silicon anions surrounded by nine metal cations; these tricapped trigonal prismatic Si@(Mg/Yb/Ba)9 polyhedra share faces to form the overall structures. Magnetic susceptibility measurements show Pauli paramagnetic behavior for all three compounds, indicating the ytterbium is divalent. The silicides have a 2:1 ratio of metal cations to silicide anions and are therefore charge-balanced. This should result in semiconducting or semimetallic behavior; the latter is supported by electronic structure calculations. The ...

U8Al19Si6 is formed from the reaction of uranium oxide and silicon in aluminum flux. Growth of this material is dependent on the presence of surface hydroxyl groups on alumina in the crucible. The compound forms as large cuboid crystals with a complex new structure that is a cubic stuffed supercell of UAl3 (AuCu3 parent structure type). It features a 4-fold expansion of the unit cell axis and the addition of atoms on two extra positions resulting in Pm3n symmetry. The ordered distribution of aluminum and silicon was determined using single crystal neutron diffraction. The magnetic susceptibility shows temperature independent paramagnetic behavior, while heat capacity measurements are consistent with Fermi liquid characteristics at low temperatures where the Sommerfeld constant is enhanced in comparison to that of a conventional metal. These bulk thermodynamic properties indicate that U8Al19Si6 is an itinerant electron Pauli paramagnet with moderately enhanced mass charge carrier quasiparticles.

Metal flux synthesis involves the reaction of metals and metalloids in a large excess of a low-melting metal that acts as a solvent. This technique makes use of an unusual temperature regime (above the temperatures used for solvothermal methods and below the temperatures used in traditional solid state synthesis) and facilitates the growth of products as large crystals. It has proven to be a fruitful method to discover new intermetallic compounds. However, little is known about the chemistry occurring within a molten metal solvent; without an understanding of the nature of precursor formation and assembly, it is difficult to predict product structures and target properties. Organic chemists have a vast toolbox of well-known reagents and reaction mechanisms to use in directing their synthesis toward a desired molecular structure. This is not yet the case for the synthesis of inorganic extended structures. We have carried out extensive explorations of the growth of new magnetic intermetallic compounds from a variety of metal fluxes. This Account presents a review of some of our results and recent reports by other groups; this work indicates that products with common building blocks and homologous series with identical structural motifs are repeatedly seen in metal flux chemistry. For instance, fluorite-type layers comprised of transition metals coordinated by eight main group metal atoms are found in the Th

Bismuth and antimony were reacted in sulfur/iodine flux mixtures at various temperatures and iodine concentrations to explore the effects of these variables on the synthesis and properties of Bi1–xSbxSI products. The products grow as crystals; microprobe elemental analysis and UV/vis/NIR spectroscopy of the Bi1–xSbxSI solid solutions indicate that substitution is homogeneous within individual crystals but varies up to 15% between crystals within each synthesis batch. Raman spectra show a two-mode behavior upon substitution, indicating covalent bonding within the structure, and TEM/SEM data confirm no presence of nanoclustering or segregation within the crystals.

Over the last 3-4 decades, solid-state chemistry has emerged as the forefront of materials design and development. The field has revolutionized into a multidisciplinary subject and matured with a scope of new synthetic strategies, new challenges, and opportunities. Understanding the structure is very crucial in the design of appropriate materials for desired applications. Professor Mercouri G. Kanatzidis has encountered both challenges and opportunities during the course of the discovery of many novel materials. Throughout his scientific career, Mercouri and his group discovered several inorganic compounds and pioneered structure-property relationships. We, a few Ph.D. and postdoctoral students, celebrate his 60th birthday by providing a Viewpoint summarizing his contributions to inorganic solid-state chemistry. The topics discussed here are of significant interest to various scientific communities ranging from condensed matter to green energy production.

Reactions of bismuth in sulfur/iodine flux mixtures were explored at various temperatures and iodine concentrations. The observed products include Bi2S3, BiSI, and Bi13S18I2. The latter compound, formerly reported as “Bi19I3S27” grows as well formed needles from the flux. This enabled extensive crystallographic studies by single crystal XRD and powder synchrotron XRD. These data allow a more accurate assignment of the disordered bismuth sites in the structure, indicating formation of subvalent Bi24+ dimers; this results in a stoichiometry of Bi13S18I2. Thermal decomposition studies and Raman spectroscopy support this structural model, and electronic structure calculations and optical reflectance studies indicate this compound is an indirect band gap semiconductor with band gap of 0.3 eV.

MgNi

Two new quaternary analogs of the Gd

The Ba/Yb/Mg/Si intermetallic system is extremely complex, with four competing structurally related compounds forming from reactions of barium, ytterbium, and silicon in magnesium-rich Mg/Al flux. In addition to the previously reported Ba2Yb0.9Mg11.1Si7, Ba5Yb2Mg17Si12, and Ba20Yb5Mg61Si43, a new compound has been found. Ba6Yb1.84Mg18.16Si13 crystallizes in the P6 space group, with the Zr6Ni20P13 structure type. Quenching experiments and in situ neutron powder diffraction studies were carried out to determine the reaction parameters that favor particular products. Under slow-cooling conditions, Ba5Yb2Mg17Si12 precipitates from the flux at 800 °C. A faster cooling rate of an identical reaction results in the formation of single crystals of Ba20Yb5Mg61Si43 in the flux at 640 °C. This indicates that the crystallization of products in this metal flux reaction does not involve precipitation and interconversion of different phases but instead depends on the rate of cooling across the supersaturated metastable zone in this system.

A cerium cobalt borocarbide intermetallic compound was grown as large crystals from reactions of boron and carbon in cerium/cobalt eutectic melt. The complex structure of the product Ce10Co2.64B11.70C10 (triclinic, P, a = 8.5131(5) A, b = 8.5144(5) A, c = 13.5709(7) A, α = 100.870(1)°, β = 93.677(1)°, γ = 90.041(1)°, Z = 2, R1 = 0.0293) features Co4 squares capped by borocarbide chains. Several disordered sites are also consistently found in the structural refinement of crystals of this phase. Magnetic susceptibility measurements show a ferromagnetic transition at 15 K and also indicate fluctuating cerium valences.

Two new tellurium-containing nitrides were grown from reactions in molten calcium and lithium. The compound Ca6Te3N2 crystallizes in space group R3̅c (a = 12.000(3)Å, c = 13.147(4)Å; Z = 6); its structure is an anti-type of rinneite (K3NaFeCl6) and 2H perovskite related oxides such as Sr3Co2O6. The compound Ca6(LixFe1-x)Te2N3 where x ≈ 0.48 forms in space group P42/m (a = 8.718(3)Å, c = 6.719(2)Å; Z = 2) with a new stuffed anti-type variant of the Tl3BiCl6 structure. Band structure calculations and easily observable red/green dichroic behavior indicate that Ca6Te3N2 is a highly anisotropic direct band gap semiconductor (Eg = 2.5 eV). Ca6(LixFe1-x)Te2N3 features isolated linear N-Fe-N units with iron in the rare Fe(1+) state. The magnetic behavior of the iron site was characterized by magnetic susceptibility measurements, which indicate a very high magnetic moment (5.16μB) likely due to a high degree of spin-orbit coupling. Inherent disorder at the Fe/Li mixed site frustrates long-range communication between magnetic centers.

The intermetallic compounds RE 6 Co 5 Ge 1+x Al 3−x (RE=Pr , Nd) were synthesized from the reaction of germanium and aluminum in RE/Co eutectic flux. These phases crystallize with the Nd 6 Co 5 Ge 2.2 structure type in hexagonal space group P -6 m 2 ( a =9.203(2)A, c =4.202(1) A, R 1 =0.0109 for Pr 6 Co 5 Ge 1.80 Al 2.20 ; and a =9.170(3) A, c =4.195(1) A, R 1 =0.0129 for Nd 6 Co 5 Ge 1.74 Al 2.26 ). The structure features chains of face-sharing Ge@RE 9 clusters intersecting hexagonal cobalt nets linked by aluminum atoms. Magnetic susceptibility measurements indicate that both phases exhibit ferromagnetic ordering of the cobalt layers with T C in the range of 130–140 K. The magnetic moments of the rare earth ions order at lower temperature (30–40 K). Magnetic measurements on oriented crystals of Nd 6 Co 5 Ge 1.74 Al 2.26 show a strong preference of the moments to order along the c -axis.

The intermetallic Nd 8 Co 4− x Al x Ge 2 C 3 ( x ≈0.65) was prepared from reaction of germanium and carbon in Nd/Co eutectic flux in an alumina crucible. This phase exhibits a new structure type in orthorhombic space group Pbcm , with unit cell parameters a =8.001(1) A, b =11.696(2) A, c =15.020(3) A ( Z =4; R 1 =0.0234). The structure features germanium-centered neodymium clusters Ge@Nd 9 which share faces to form layers separated by zigzag chains of cobalt atoms capped by carbon. Density of states calculations confirm that this compound is metallic, and indicate that the cobalt should not have a magnetic moment. This is supported by magnetic susceptibility measurements which show a low temperature ferromagnetic ordering at T C =50 K due to the Nd 3+ ions. Magnetization field dependence studies on single crystals indicate this compound is a strong ferromagnet with large anisotropy; the Nd 3+ magnetic moments align along the a -axis.

X-ray diffraction, magnetic susceptibility, magnetization, heat capacity and electrical resistivity results are reported for single crystals of two structural variants of EuNi2-δ Sb2 that crystallize in the CaBe2Ge2 and ThCr2Si2-type structures. While the former occurs with a stoichiometric ratio, the latter exhibits a Ni site vacancy (δ = 0.36). Both systems exhibit similar magnetic behavior at elevated temperatures, where there is an isotropic Curie-Weiss temperature dependence that indicates an antiferromagnetic exchange interaction between divalent europium ions, although it is stronger for the CaBe2Ge2-variant. At low temperatures, the differing structural environments that surround the Eu ions result in distinct ordering behavior. The CaBe2Ge2-variant orders antiferromagnetically near T N1 = 6.9 K and then undergoes a first order phase transition at T M = 4.6 K. The ThCr2Si2-variant exhibits simpler behavior, with antiferromagnetic ordering at T N2 = 5.6 K. For both compounds, an applied magnetic field suppresses the ordering temperatures and induce metamagnetic phase transitions, while applied pressure causes the ordering temperatures to increase. From these results, EuNi2-δ Sb2 emerges as a useful system in which to study the impact of structural variation on magnetism in a Eu-based metal.

Reactions of silicon, carbon, and iron in a low-melting flux mixture of praseodymium and nickel produced two competing intermetallic compounds. Pr

Single crystals of Mg-substituted CeFe{sub 2}Al{sub 8} type intermetallics RFe{sub 2}Mg{sub x}Al{sub 8–x} (R=La–Nd and Sm; x≤1) were grown by reacting iron and rare earth metals in 1:1 Mg/Al mixed flux. The structure features mono-capped and bi-capped trigonal prismatic FeAl{sub 6} units. Electronic structure calculations indicate that magnesium substitution reduces the valence electron count, shifting the Fermi level away from a pseudo-gap. This changes the electronic nature of the cerium analog; the previously reported ternary CeFe{sub 2}Al{sub 8} shows strong hybridization between the cerium states and the conduction electrons, resulting in no magnetic moment on Ce atoms. On the other hand, magnetic susceptibility measurements on CeFe{sub 2}Mg{sub x}Al{sub 8–x} indicates a localized moment on cerium. The newly synthesized Pr, Nd and Sm analogs exhibit antiferromagnetic ordering at 2.8 K, 7.8 K and 12 K respectively. Solid state {sup 27}Al NMR of LaFe{sub 2}Mg{sub x}Al{sub 8–x} exhibits a broad Knight shift at ~1200 ppm, consistent with the metallic behavior shown by electrical resistivity data. - Graphical abstract: Mg substitution into CeFe{sub 2}Al{sub 8} modifies cerium valence due to changing valence electron count. - Highlights: • RFe{sub 2}Mg{sub x}Al{sub 8−x} (R=La–Nd, Sm) grow as large crystals from reactions in Mg/Al flux. •more » Products are magnesium-substituted variants of CeFe{sub 2}Al{sub 8}, with CaCo{sub 2}Al{sub 8} structure. • Ce magnetic moment in CeFe{sub 2}Mg{sub x}Al{sub 8−x} varies from that in CeFe{sub 2}Al{sub 8} due to VEC change. • Antiferromagnetic ordering observed for Pr, Nd, Sm analogs of RFe{sub 2}Mg{sub x}Al{sub 8−x}.« less

Reactions of tin and manganese in a lanthanum/nickel eutectic melt in alumina crucibles produce La

Reactions of indium and silicon with lithium nitride in Ca/Li flux produce two new nitridosilicates: Ca

The reaction of arsenic with sources of light elements in a Ca/Li melt leads to the formation of two new arsenide hydride phases. The predominant phase Ca14As6X7 (X = C4–, N3–, H–) exhibits a new tetragonal structure type in the space group P4/mbm (a = 15.749(1) A, c = 9.1062(9) A, Z = 4, R1 = 0.0150). The minor phase LiCa3As2H also has a new structure type in the orthorhombic space group Pnma (a = 11.4064(7) A, b = 4.2702(3) A, c = 11.8762(8)A, Z = 4, R1 = 0.0135). Both phases feature hydride and arsenide anions separated by calcium cations. The red color of these compounds indicates they should be charge-balanced. DOS calculations on LiCa3As2H confirm a band gap of 1.4 eV; UV–vis spectroscopy on Ca14As6X7 shows a band gap of 1.6 eV. Single-crystal neutron diffraction studies were necessary to determine the mixed occupancy of carbon, nitrogen, and hydrogen anions on the six light-element sites in Ca14As6X7; these data indicated an overall stoichiometry of Ca14As6C0.445N1.135H4.915.

The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) Å, b = 6.094(5) Å, c = 8.903(8) Å (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments.

Reactions of CaH2 with group 13 metals in a 1:1 Ca/Li flux mixture produce Ca54In13B4–xH23+x (2.4 < x < 4). This compound has a complex new structure [Im3, a = 16.3608(6) A, Z = 2] which can be viewed as a body-centered cubic array of Bergman-related clusters that are composed of a central indium atom surrounded by an icosahedron of 12 calcium atoms; hydride ions cap each face, forming a pentagonal dodecahedron that is further surrounded by a calcium shell. These In@Ca12@H20@Ca30 clusters are surrounded by a disordered calcium indium hydride network. Indium is not completely reduced by the flux; the structure features ionic hydride regions and metallic calcium indium regions, confirmed by electronic structure calculations and 1H and 115In solid-state NMR spectroscopy. This compound can therefore be viewed as a “subhydride”, akin to the alkali metal suboxides that feature ionic oxide clusters surrounded by metallic regions.

Four new intermetallic phases R3-δFeAl4-xMgxSi2 (R = Yb, Dy) and R3-δFeAl4-xMgxGe2 (R = Er, Y) were synthesized in Mg/Al (1:1 mol ratio) molten flux. These phases have a new structure type in tetragonal space group P4/mbm (a = 13.3479(9) A, c = 4.0996(3) A, Z = 4, and R1 = 0.0176 for Yb2.77FeAl3.72Mg0.28Si2). The structure features iron in trigonal prismatic coordination by aluminum atoms. The prisms share trigonal faces to form chains running along the c-axis, similar to the chains seen in several related structures, including that of the previously reported competing phases R5Mg5Fe4Al12Si6 (R = Gd, Dy, and Y). Occupancies of Mg, Al, and Si sites in Yb2.77FeAl3.72Mg0.28Si2 were determined by single crystal X-ray and neutron diffraction, bond length analysis, and comparison to atom positions and bond lengths in the isostructural germanides. Electronic structure calculations indicate these phases are polar intermetallics with pseudogaps near the Fermi level. The magnetic properties of these phases are dete...

The intermetallic Nd 8 Co 4− x Al x Ge 2 C 3 ( x ≈0.65) was prepared from reaction of germanium and carbon in Nd/Co eutectic flux in an alumina crucible. This phase exhibits a new structure type in orthorhombic space group Pbcm , with unit cell parameters a =8.001(1) A, b =11.696(2) A, c =15.020(3) A ( Z =4; R 1 =0.0234). The structure features germanium-centered neodymium clusters Ge@Nd 9 which share faces to form layers separated by zigzag chains of cobalt atoms capped by carbon. Density of states calculations confirm that this compound is metallic, and indicate that the cobalt should not have a magnetic moment. This is supported by magnetic susceptibility measurements which show a low temperature ferromagnetic ordering at T C =50 K due to the Nd 3+ ions. Magnetization field dependence studies on single crystals indicate this compound is a strong ferromagnet with large anisotropy; the Nd 3+ magnetic moments align along the a -axis.

The intermetallic compounds Ln6Co5Ge1.80Al2.20 (Ln: Pr, Nd) are prepared by reactions of Ge and Al in a reactive Ln/Co flux (alumina crucible, 950 °C, 12 h, annealing at 650 °C for 84 h).

New carbide Zintl phases Ca(11)E(3)C(8) (E = Sn, Pb) were grown from reactions of carbon and heavy tetrelides in Ca/Li flux. They form with a new structure type in space group P2(1)/c (a = 13.1877(9)Å, b = 10.6915(7)Å, c = 14.2148(9)Å, β = 105.649(1)°, and R(1) = 0.019 for the Ca(11)Sn(3)C(8) analog). The structure features isolated E(4-) anions as well as acetylide (C(2)(2-)) and allenylide (C(3)(4-)) anions; the vibrational modes of the carbide anions are observed in the Raman spectrum. The charge-balanced nature of these phases is confirmed by DOS calculations which indicate that the tin analog has a small band gap (E(g)0.1 eV) and the lead analog has a pseudogap at the Fermi level. Reactions of these compounds with water produce acetylene and allene.

R(33)Fe(14-x)Al(x+y)B(25-y)C(34) (R = La or Ce; x ≤ 0.9; y ≤ 0.2) and R(33)Fe(13-x)Al(x)B(18)C(34) (R = Ce or Pr; x0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im3m (a = 14.617(1) Å, Z = 2, R(1) = 0.0155 for Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34), and a = 14.246(8) Å, Z = 2, R(1) = 0.0142 for Ce(33)Fe(13)B(18)C(34)). Their structures can be described as body-centered cubic arrays of large Fe(13) or Fe(14) clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and Mössbauer data show that the boron-centered Fe(14) clusters in Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce(3+/4+) valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce(33)Fe(13)B(18)C(34) indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T(C) = 180 K is due to magnetic moments on the Fe(13) clusters.

Recent work on the growth of complex oxides in salt fluxes is reviewed. Single crystals of Cs0.33MoO3, CsFe(MoO4)2 and the new phase, Cs2Mo0.65O0.21Cl5.44, have been grown from the reaction of metal oxides Fe2O3, MoO3 and molybdenum powder in a eutectic CsCl/NaCl flux. Cs0.33MoO3 is one of the known molybdenum bronzes, featuring mixed valent molybdenum ions. CsFe(MoO4)2 has a layered KAl(MoO4)2 structure, which consists of infinite slabs of corner-sharing MoO4 and FeO6 polyhedra separated by layers of Cs+ cations. Cs2Mo0.65O0.21Cl5.44 forms with a new structure type (orthorhombic, Cmcm, a = 7.434(1) A, b = 17.330(3) A, c = 8.074(1) A, Z = 4) which is comprised of isolated [Mo(O/Cl)Cl5] octahedra embedded in a distorted CsCl matrix. Magnetic susceptibility measurements indicate antiferromagnetic ordering for both CsFe(MoO4)2 (T N = 4.5 K) and Cs2Mo0.65O0.21Cl5.44 (T N = 7 K).

Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1 Mg/Al mixed flux produce well-formed crystals of R(5)Mg(5)Fe(4)Al(x)Si(18-x) (x ≈ 12). These phases have a new structure type in tetragonal space group P4/mmm (a = 11.655(2) Å, c = 4.0668(8) Å, Z = 1 and R(1) = 0.0155 for the Dy analogue). The structure features two rare earth sites and one iron site; the latter is in monocapped trigonal prismatic coordination surrounded by silicon and aluminum atoms. Siting of Al and Si was investigated using bond length analysis and (27)Al and (29)Si MAS NMR studies. The magnetic properties are determined by the R elements, with the Gd and Dy analogues exhibiting antiferromagnetic ordering at T(N) = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic behavior with varying field.

Reactions of germanium in calcium/lithium flux yield crystals of new complex hydrides, with hydrogen incorporated either inadvertently due to traces of hydride contaminants in the flux metals, or deliberately by the addition of CaH2 as a reactant. The new germanide hydride Zintl phase LiCa7Ge3H3 crystallizes in the orthorhombic space group Pnma [a = 9.8599(2) A, b = 13.7716(3) A, c = 8.7430(2) A; Z = 4; R1 = 0.0195]. The structure features isolated Ge4– anions surrounded by calcium ions, and hydride anions in octahedral sites defined by Ca and Li ions. Another product thatappears in these reactions was found to form from incorporation of both oxide and hydride impurities. This phase,LiCa11Ge3OHx (x ≈ 4) forms in the tetragonal space group P42/nmc [a = 15.832(2) A, c = 13.694(2) A; Z = 8; R1 = 0.0350]. In addition to isolated Ge4– and octahedral H– anions, the structure also features incorporation of oxide anions in octahedral sites.

The intermetallic compound Co{sub 7+x}Zn{sub 3-x}Sn{sub 8} (-0.2 Co{sub 7+x}Zn{sub 3-x}Sn{sub 8} grows from reaction of cobalt in Zn/Sn eutectic flux. > Varying Co in reaction stoichiometry yields Cmcm subcell or Pnma supercell structure. > Co{sub 7+x}Zn{sub 3-x}Sn{sub 8} structural building blocksmore » similar to those in CoSn binary phase. > Co{sub 7+x}Zn{sub 3-x}Sn{sub 8} forms from reaction of CoSn in the Zn/Sn flux.« less

Crystals of La21−δMn8M7C12 (M = main group elements Ge/Al, Sn, Sb, Te, Bi) were synthesized in La/Ni eutectic flux. The structure features tetrahedral manganese clusters edge-capped by carbon atoms, Mn4C6, embedded into a nonmagnetic La/M network. The structures were determined from single-crystal X-ray diffraction (La21Mn8Ge6.2Al0.8C12, Fm3m; a = 16.2259(3) A; Z = 4; R1 = 0.022). While most of the La21Mn8M7C12 analogues are completely ordered, the M = Te compound features partial occupancy of one of the La sites, and the M = Ge analogue exhibits mixed Ge/Al occupancy on one of the M sites. La21−δMn8M7C12 with M = Sn, Sb, Te, Bi are paramagnets, but the susceptibility of La21Mn8Ge6.2Al0.8C12 exhibits ZFC-FC divergence at T1 ≈ 6 K and an additional feature at T2 ≈ 3 K. Such behavior is indicative of frustration of antiferromagnetically coupled manganese magnetic moments within the Mn4 tetrahedra. AC susceptibility measurements confirm the presence of two cusps at T1 and T2; however, no frequency dependenc...

Crystals of the ternary La{sub 11}(MnC{sub 6}){sub 3} and new quaternary carbide La{sub 14}Sn(MnC{sub 6}){sub 3} phases were grown from La/Ni eutectic flux and their structures were determined by means of X-ray single crystal diffraction. La{sub 11}(MnC{sub 6}){sub 3} is a new superstructure variant of La{sub 3.67}MnC{sub 6} (previously reported disordered subcell: P6{sub 3}/m; a{sub 0}=8.806 A; c{sub 0}=5.329 A, Z=2). The superstructure (R3-bar ; a={radical}3a{sub 0}=15.2649(9) A; c=3c{sub 0}=16.013(1) A, Z=6; R{sub 1}=0.022) is realized by complete ordering of the La chains within the columns of face-sharing carbon octahedra, with alternating La-La distances leading to R-centering and enlargement of the unit cell. The structure of the quaternary carbide La{sub 14}Sn(MnC{sub 6}){sub 3} (P6-bar ; a=8.756(1) A; c=10.483(2) A, Z=1; R{sub 1}=0.026) is closely related to that of La{sub 11}(MnC{sub 6}){sub 3} with part of the MnC{sub 6} units replaced by Sn atoms. The structure and precise composition of La{sub 14}Sn(MnC{sub 6}){sub 3} can be derived from that of La{sub 11}(MnC{sub 6}){sub 3} by taking into account the extent of this substitution and variation in lanthanum siting in the chain of carbon octahedra. Band structure calculations indicate both phases are metallic; the La{sub 11}(MnC{sub 6}){sub 3} phase is stabilized bymore » the ordering of La atoms which induces a pseudogap at E{sub F}. -- La{sub 11}(MnC{sub 6}){sub 3} with fully ordered superstructure and a new carbide La{sub 14}Sn(MnC{sub 6}){sub 3} were obtained from La/Ni eutectic flux. Display Omitted« less

Single crystals of a new reduced vanadate phase, Cs(5)FeV(5)O(13)Cl(6), have been grown from the reaction of metal oxides V(2)O(5) and Fe(2)O(3) in the presence of a metal reducing agent in a eutectic CsCl/NaCl flux. This compound adopts a tetragonal structure (P4/nmm, a = 10.943(3) A, c = 10.535(4) A, Z = 2) that consists of reduced vanadate layers separated by ionic layers comprised of [FeCl(6)](3-) anions and Cs(+) cations. There are two distinct vanadium sites in the structure of this compound; V(4+) is in square pyramidal configuration, and V(5+) has a tetrahedral coordination environment. The (51)V NMR Knight shift and the magnetic susceptibility data indicate the delocalization of the unpaired electron of vanadium. Ferrimagnetic ordering is observed at 5 K.