ABSTRACT
Alloys from the ternary Li-Al-Sn system have been investigated with respect to possible applications as negative electrode materials in Li-ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li13Sn5 binary compound. The ternary stannide, Li9Al4Sn5 (nonalithium tetraaluminium pentastannide; trigonal, P-3m1, hP18), crystallizes as a new structure type, which is an ordered variant of the binary Li13Sn5 structure type. One Li and one Sn site have -3m. symmetry, and all other atoms occupy sites of 3m. symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al4Sn5]m- polyanion.
ABSTRACT
Penta-zirconium copper tribismuth, Zr5CuBi3, crystallizes in the hexa-gonal Hf5CuSn3 structure type. The asymmetric unit contains two Zr sites (site symmetries 3.2 and m2m), one Cu site (site symmetry 3.m) and one Bi site (site symmetry m2m). The environment of the Bi atoms is a tetra-gonal anti-prism with one added atom and a coordination number (CN) of 9. The polyhedron around the Zr1 atom is a defective cubo-octa-hedron with CN = 11. The bicapped hexa-gonal anti-prism (CN = 14) is typical for Zr2 atoms. The Cu atom is enclosed in a eight-vertex polyhedron (octa-hedron with two centered faces). The metallic type of bonding was indicated by an analysis of the inter-atomic distances and electronic structure calculation data.
ABSTRACT
The quaternary thulium nickel/lithium distannide, TmNi1-x Li x Sn2 (x = 0.035), crystallizes in the ortho-rhom-bic LuNiSn2 structure type. The asymmetric unit contains three Tm sites, six Sn sites, two Ni sites and one Ni/Li site [relative occupancies = 0.895â (8):0.185â (8)]. Site symmetries are .m. for all atoms. The 17-, 18- and 19-vertex distorted pseudo-Frank-Kasper polyhedra are typical for all Tm atoms. Four Sn atoms are enclosed in a 12-vertex deformed cubo-octa-hedron, and another Sn atom is enclosed in a penta-gonal prism with three added atoms. A tricapped trigonal prism is typical for a further Sn atom. The coordination number for all Ni atoms and Ni/Li statistical mixtures is 12 (fourcapped trigonal prism [Ni/LiTm5Sn5]). Tm atoms form the base of a prism and Ni/Li atoms are at the centres of the side faces of an [SnTm6Ni/Li3] prism. These isolated prisms are implemented into three-dimensional-nets built out of Sn atoms. Electronic structure calculations using TB-LMTO-ASA suggest that the Tm and Ni/Li atoms form positively charged n[TmNi/Li] (m+) polycations which compensate the negative charge of 2n[Sn] (m-) polyanions. Analysis of the inter-atomic distances and electronic structure calculations indicate the dominance of a metallic type of bonding.
ABSTRACT
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.
ABSTRACT
New ternary dodecalithium dodecacopper tetradecaaluminium, Li(12)Cu(12.60)Al(14.37) (trigonal, R Ì 3m, hR39), crystallizes as a new structure type and belongs to the structural family that derives from binary Laves phases. The Li atoms are enclosed in 15- and 16-vertex and the Al3 atom in 14-vertex pseudo-Frank-Kasper polyhedra. The polyhedra around the statistical mixtures of (Cu,Al)1 and (Al,Cu)2 are distorted icosahedra. The electronic structure was calculated by the TB-LMTO-ASA (tight-binding linear muffin-tin orbital atomic spheres approximation) method. The electron localization function, which indicates bond formation, is mostly located at the Al atoms. Thus, Al-Al bonding is much stronger than Li-Al or Cu-Al bonding. This indicates that, besides metallic bonding which is dominant in this compound, weak covalent Al-Al interactions also exist.
ABSTRACT
The new ternary phase penta-terbium lithium tris-tannide, Tb(5)LiSn(3), crystallizes in the hexa-gonal Hf(5)CuSn(3) structure type, which is a 'filled' version of the binary RE(5)Sn(3) phases (Mn(5)Si(3)-type) (RE is rare earth). The asymmetric unit contains two Tb sites (site symmetries 3.2 and m2m), one Li site (site symmetry [Formula: see text].m) and one Sn site (site symmetry m2m). The 14-vertex Frank-Kasper polyhedra are typical for Li and Tb atoms. The environment of the Sn atom is a pseudo-Frank-Kasper polyhedron with a coordination number of 13 for the tin atom. One of the Tb atoms is enclosed in a 17-vertex polyhedron. The metallic type of bonding was indicated by an analysis of the inter-atomic distances.
ABSTRACT
The new ternary lithium copper aluminide, Li(12)Cu(16+x)Al(26-x) (x = 3.2), dodecalithium nonadecacopper tricosaaluminide, crystallizes in a new structure type with space group P4/mbm. Among nine independent atomic positions, two Al (one of which is statistically disordered with Cu) and three Li atoms have point symmetry m.2m, two statistically disordered Al/Cu atoms are in m.. sites, one Al atom is in a 4/m.. site and one Cu atom occupies a general site. The framework of Li(12)Cu(16+x)Al(26-x) consists of pseudo-Frank-Kasper polyhedra enclosing channels of hexagonal prisms occupied by Li atoms. The crystallochemical peculiarity of this new structure type is discussed in relation to the derivatives from Laves phases (LiCuAl(2) and Li(8)Cu(12+x)Al(6-x)) and to the well known CaCu(5) structure.
ABSTRACT
The new ternary lithium copper aluminide Li(8)Cu(12+x)Al(6-x) (x = 1.16) crystallizes in the P6(3)/mmc space group with six independent atom positions of site symmetries 3m. (Al/Cu mixture), 6m2 (Li atoms), 3m. (Al/Cu mixture and Li atoms) and .m. (Cu atoms). The compound is a derivative of the K(7)Cs(6) binary structure type and is related to the binary MgZn(2) Laves phase and the LiCuAl(2), MgCu(1.07)Al(0.93) and Mg(Cu(1-x)Al(x))(2) (x = 0.465) ternary Laves phases. The coordination polyhedra of the atoms in this structure are icosahedra (Cu atoms), slightly distorted icosahedra and bicapped hexagonal antiprisms (Al/Cu statistical mixture), and Frank-Kasper and distorted Frank-Kasper polyhedra (Li atoms). All interatomic distances indicate metallic type bonding.
