A new ternary derivative of the Laves phases in the Mg-Co-Ga system.

Crystal structures of MgCoGa, Mg0.74CoGa0.52 and Mg0.49CoGa0.15 phases from the Mg-Co-Ga system were investigated using single-crystal diffraction. These structures belong to the family of so-called Laves phases. Hexagonal MgCoGa crystallizes as a disordered phase within the MgZn2 structure type. The orthorhombic structure of Mg0.74CoGa0.52 is a distortion variant of MgZn2 and URe2 structure type, and the structural relation is demonstrated in terms of a Bärnighausen formalism group-subgroup transformation scheme. The structure of trigonal phase Mg0.49CoGa0.15 is strongly disordered, as is shown by the presence of adjacent atomic sites which cannot be occupied simultaneously. In Mg0.49CoGa0.15, two subcells (A and B) were obtained in a ratio of 9:1. Subcell A is closely related to MgZn2-type.

New cubic cluster phases in the Mg-Ni-Ga system.

The crystal structure of new Mg9Ni6Ga14 and Mg3Ni2Ga compounds were investigated by single-crystal diffraction. Both structures can be described as three-core-shell cluster compounds. In the Mg6Ni9Ga14 structure, the [Ni6Ga6] icosahedron is encapsulated within the [Mg20] dodecahedron, which is again encapsulated within a [Ni18Ga42] fullerene-like truncated icosahedron, thus the three core-shell cluster [Ni6Ga6@Mg20@Ni18Ga42] results. In the Mg3Ni2Ga structure, the [Mg6] octahedron is encapsulated within the [Ni12Ga6] flattened icosahedron in vertices of which there are 12 nickel atoms, and six lateral edges are centered by gallium atoms, which in turn is encapsulated within a [Mg36] pseudo-rhombicuboctahedron with 12 additional atoms centering the lateral faces; thus for Mg3Ni2Ga the three-shell cluster is [Mg6@Ni12Ga6@Mg36].

A new monoclinic structure type for ternary gallide MgCoGa2.

The crystal structure of MgCoGa2 (magnesium cobalt digallide) was solved by direct methods and refined in two space groups as P21/c (standard choice) and P21/n (non-standard choice). The refined lattice parameters for the standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 8.0264 (3) Šand ß = 125.571 (3)°, and for the non-standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 6.5464 (2) Šand ß = 94.217 (3)°. All parameters for MgCoGa2 refined to R1 = 0.027 and wR2 = 0.042 using 594 reflections. The crystal structure peculiarities of this compound are discussed. Particular attention has been given to relationships with other similar structures, such as YPd2Si and Fe3C. Crystallographic analysis, together with linear muffin-tin orbital electronic structure calculations, reveals the presence of three-dimensional polyatomic nets with partial covalent bonding between the Ga atoms.

Li4Ge2B as a new derivative of the Mo2B5 and Li5Sn2 structure types.

Binary and multicomponent intermetallic compounds based on lithium and p-elements of Groups III-V of the Periodic Table are useful as modern electrode materials in lithium-ion batteries. However, the interactions between the components in the Li-Ge-B ternary system have not been reported. The structure of tetralithium digermanium boride, Li4Ge2B, exhibits a new structure type, in the noncentrosymmetric space group R3m, in which all the Li, Ge and B atoms occupy sites with 3m symmetry. The title structure is closely related to the Mo2B5 and Li5Sn2 structure types, which crystallize in the centrosymmetric space group R-3m. All the atoms in the title structure are coordinated by rhombic dodecahedra (coordination number = 14), similar to the atoms in related structures. According to electronic structure calculations using the tight-binding-linear muffin-tin orbital-atomic spheres approximation (TB-LMTO-ASA) method, strong covalent Ge-Ge and Ge-B interactions were established.

Grown from lithium flux, the ErCo5Si(3.17) silicide is a combination of disordered derivatives of the UCo5Si3 and Yb6Co30P19 structure types.

A ternary hexaerbium triacontacobalt enneakaidecasilicide, ErCo5Si(3.17), crystallizes as a combination of disordered variants of the hexagonal UCo5Si3 (P63/m) and Yb6Co30P19 (P6) structure types and is closely related to the Sc6Co30Si19 and Ce6Rh30Si19 types. The Er, Co and three of the Si atoms occupy sites of m.. symmetry and a fourth Si atom occupies a site of -6.. symmetry. The environment of the Er atom is a 21-vertex pseudo-Frank-Kasper polyhedron. Trigonal prismatic coordination is observed for the Si atoms. The Co atoms are enclosed in heavily deformed cuboctahedra and 11-vertex polyhedra. Crystallochemistry analysis and the data from electronic structure calculations (TB-LMTO-ASA) suggest that the Er atoms form positively charged cations which compensate the negative charge of the [Co12Si9](m-) polyanions.

The Ce2Li0.39Ni1.61Si2 structure as a new derivative of the AlB2 family.

A new quaternary dicerium lithium/nickel disilicide, Ce2Li0.39Ni1.61Si2, crystallizes as a new structure type of intermetallic compounds closely related to the AlB2 family. The crystal-chemical interrelationships between parent AlB2-type, BaLiSi, ZrBeSi and the title compound are discussed using the Bärnighausen formalism. Two Ce atoms occupy sites of 3m. symmetry. The remainder, i.e. Ni, mixed Ni/Li and Si atoms, occupy sites of -6m2 symmetry. The environment of the Ce atom is an 18-vertex polyhedron and the Ni, Ni/Li and Si atoms are enclosed in tricapped trigonal prisms. The title structure can be assigned to class No. 10 (trigonal prism and its derivatives) according to the Krypyakevich classification scheme [Krypyakevich (1977). In Structure Types of Intermetallic Compounds. Moscow: Nauka]. The electronic structure of the title compound was calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA). Metallic bonding is dominant in this compound. The strongest interactions are Ni-Si and Ce-Si.

Tm2.22Co6Sn20 and TmLi2Co6Sn20 stannides as disordered derivatives of the Cr23C6 structure type.

A new ternary dithulium hexacobalt icosastannide, Tm2.22Co6Sn20, and a new quaternary thulium dilithium hexacobalt icosastannide, TmLi2Co6Sn20, crystallize as disordered variants of the binary cubic Cr23C6 structure type (cF116). 48 Sn atoms occupy sites of m.m2 symmetry, 32 Sn atoms sites of .3m symmetry, 24 Co atoms sites of 4m.m symmetry, eight Li (or Tm in the case of the ternary phase) atoms sites of -3 symmetry and four Tm atoms sites of m3m symmetry. The environment of one Tm atom is an 18-vertex polyhedron and that of the second Tm (or Li) atom is a 16-vertex polyhedron. Tetragonal antiprismatic coordination is observed for the Co atoms. Two Sn atoms are enclosed in a heavily deformed bicapped hexagonal prism and a monocapped hexagonal prism, respectively, and the environment of the third Sn atom is a 12-vertex polyhedron. The electronic structures of both title compounds were calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA). Metallic bonding is dominant in these compounds, but the presence of Sn-Sn covalent dumbbells is also observed.

Terbium (lithium zinc) distannide, TbLi(1-x)Zn(x)Sn(2) (x = 0.2).

The new terbium (lithium zinc) distannide, TbLi(1-x)Zn(x)Sn(2) (x = 0.2) crystallizes in the ortho-rhom-bic CeNiSi(2) structure type with space group Cmcm and Pearson symbol oS16. Of the four independent 4c atom positions (m2m site symmetry), three are fully occupied by individual atoms (two by Sn and one by Tb atoms) and the fourth is occupied by Li and Zn atoms with a statistical distribution. The Tb coordination polyhedron is a 21-vertex pseudo-Frank-Kasper polyhedron. One Sn atom is enclosed in a tricapped trigonal prism, the second Sn atom is in a cubocta-hedron and the statistically distributed (Li,Zn) site is in a tetra-gonal anti-prism with one added atom. Electronic structure calculations were used for the elucidation of reasons for and the ability of mutual substitution of lithium and transition metals. Positive charge density was observed around the rare earth atom and the Li and Zn atoms, the negative charge density in the proximity of the Sn atoms.

Redetermination of LaZn(5) based on single crystal X-ray diffraction data.

The crystal structure of the already known binary title compound LaZn(5) (lanthanum penta-zinc) (space group P6/mmm, Pearson symbol hP6, CaCu(5) structure type) has been redetermined from single-crystal X-ray diffraction data. In contrast to previous determinations based on X-ray powder data [Nowotny (1942). Z. Metallkd.34, 247-253; de Negri et al. (2008). Inter-metallics, 16, 168-178], where unit-cell parameters and assignment of the structure type were reported, the present study reveals anisotropic displacement parameters for all atoms. The crystal structure consists of three crytallographically distinct atoms. The La atom (Wyckoff site 1a, site symmetry 6/mmm) is surrounded by 18 Zn atoms and two La atoms. The coordination polyhedron around one of the Zn atoms (Wyckoff site 2c, site symmetry -6m2) is an icosa-hedron made up from three La and nine Zn atoms. The other Zn atom (Wyckoff site 3g, site symmetry mmm) is surrounded by four La and eight Zn atoms. Bonding between atoms is explored by means of the TB-LMTO-ASA (tight-binding linear muffin-tin orbital atomic spheres approximation) program package. The positive charge density is localized around La atoms, and the negative charge density is around Zn atoms, with weak covalent bonding between the latter.