Volodymyr Pavlyuk

New Ternary Germanides La4Mg5Ge6 and La4Mg7Ge6: Crystal Structure and Chemical Bonding

The synthesis, structural characterization, and chemical-bonding peculiarities of the two new polar lanthanum-magnesium germanides La(4)Mg(5)Ge(6) and La(4)Mg(7)Ge(6) are reported. The crystal structures of these intermetallics were determined by single-crystal X-ray diffraction analysis. The La(4)Mg(5)Ge(6) phase crystallizes in the orthorhombic Gd(4)Zn(5)Ge(6) structure type [Cmc2(1), oS60, Z = 4, a = 4.5030(7) Å, b = 20.085(3) Å, c = 16.207(3) Å, wR2 = 0.0451, 1470 F(2) values, 93 variables]. The La(4)Mg(7)Ge(6) phase represents a new structure type with a monoclinic unit cell [C2/m, mS34, Z = 2, a = 16.878(3) Å, b = 4.4702(9) Å, c = 12.660(3) Å, β = 122.25(3)°, wR2 = 0.0375, 1466 F(2) values, 54 variables]. Crystallographic analysis together with linear muffin-tin orbital band structure calculations reveals the presence of strongly bonded 3D polyanionic [Mg-Ge] networks balanced by positively charged La atoms in both stoichiometric compounds. The La(4)Mg(5)Ge(6) compound is related to Zintl phases, showing a prominent density of states pseudogap at the Fermi level. A distinctive feature of the La(4)Mg(5)Ge(6) structure is the presence of Ge-Ge covalent dumbbells; in La(4)Mg(7)Ge(6), the higher Mg content generates a polyanionic network consisting exclusively of Mg-Ge heterocontacts. Nevertheless, the frameworks of the two phases are structurally similar, as is highlighted in this work.

Phase equilibria and crystal structure of compounds in the Fe-Zn-Sb system at 570 K

Abstract By means of X-ray structural analysis, the isothermal section of the Fe–Zn–Sb phase diagram at 570 K has been built. Two ternary compounds have been found. The FeZnSb 2 compound crystallized in the NiAs structure type, and the FeZnSb compound in the MgAgAs structure type. The crystal structure of FeSb 2 (FeS 2 structure type) has been refined by single crystal diffraction.

Crystal structure of the new compound Ce3Pt23Ge11

Abstract The crystal structure of the compound Ce3Pt23Ge11 has been determined by X-ray analysis of a single crystal (Enraf-Nonius CAD-4 autodiffractometer, Mo Kα radiation, 276 independent reflections, R-factor 0.0735 in isotropic approximation). This structure has been found to belong to a new structural type: space group F 4 3m, a = 17.1833(9) A , Z = 8 . The coordination polyhedra of the cerium atoms are compressed cubes, those of platinum have eight or 10 apexes and those of germanium are either trigonal prisms with an additional atom or cubes. The magnetic properties of Ce3Pt23Ge11 at low temperatures (4–100 K) were investigated. A diffuse magnetic phase transition at around 10 K was detected.

Li(Al 1– z Zn z ) alloys as anode materials for rechargeable Li-ion batteries

The cycling behavior of anode materials based on alloys from the Li(Al 1– z Zn z ) continuous solid solution has been studied. The performance of the most promising composition Li(Al 0.8 Zn 0.2 ) was tested in half-cells against metallic Li with three different electrolytes and in full Li-ion cells against a V 2 O 5 cathode. The underlying structure evolution during cycling and the most relevant fatigue mechanisms are elucidated by x-ray diffraction, nuclear magnetic resonance, and x-ray photoelectron spectroscopy, and reveal a loss of mobile Li due to the ongoing formation of solid electrolyte interfaces. An enhanced stability for Li(Al 1– z Zn z ) electrodes with z ˜0.2 results from a peculiar microstructure due to the decomposition of Al and Zn in the Li-poor state and their intermixing in the Li-rich state.

Anti-Mackay Polyicosahedral Clusters in La-Ni-Mg Ternary Compounds: Synthesis and Crystal Structure of the La43Ni17Mg5New Intermetallic Phase

The crystal structure of the complex La(43)Ni(17)Mg(5) ternary phase was solved and refined from X-ray single crystal diffraction data. It is characterized by a very large unit cell and represents a new structure type: La(43)Ni(17)Mg(5) - orthorhombic, Cmcm, oS260, a = 10.1895(3), b = 17.6044(14), c = 42.170(3) A, Z = 4, wR1 = 0.0598, wR2 = 0.0897, 4157 F(2) values, 176 variables. The crystal structures of the La-rich La-Ni-Mg intermetallic phases La(4)NiMg, La(23)Ni(7)Mg(4), and La(43)Ni(17)Mg(5) have been comparatively analyzed. The constitutive fragments of these structures are binary polyicosahedral core-shell clusters of Mg(4)La(22) and Mg(5)La(24) compositions together with binary polytetrahedral clusters of nickel and lanthanum atoms. The structures of the Mg-La clusters are described in detail as a unique feature of the analyzed intermetallic phases; the dodecahedral Voronoi polyhedra are proposed as a useful tool to characterize polyicosahedral clusters. The arrangements of the building units in the studied phases show some regularities; particularly the i(4)3, i(5)3 and L-i(4) units, made up of polyicosahedral clusters and analogous to the Kreiner i(3) and L units, are proposed as structural blocks.

Structure Refinement of Orthorhombic MnAl3

Structure refinement on a crystal of composition Mn 3 Al 10 were performed in space groups Pnma and Pn2 1 a (standard setting Pna2 1 ). The space group Pnma was found to be correct.

Lanthanum tetrazinc, LaZn4

The structure of lanthanum tetrazinc, LaZn(4), has been determined from single-crystal X-ray diffraction data for the first time, approximately 70 years after its discovery. The compound exhibits a new structure type in the space group Cmcm, with one La atom and two Zn atoms occupying sites with m2m symmetry, and one Zn atom occupying a site with 2.. symmetry. The structure is closely related to the BaAl(4), La(3)Al(11), BaNi(2)Si(2) and CaCu(5) structure types, which can be presented as close-packed arrangements of 18-vertex clusters, in this case LaZn(18). The kindred structure types contain related 18-vertex clusters around atoms of the rare earth or alkaline earth metal.

Polymorphism of Li2Zn3

Crystal structures of low- and high-temperature modifications of the binary phase Li(2)Zn(3) were determined by single-crystal X-ray diffraction techniques. The low-temperature modification is a disordered variant of Li(5)Sn(2), space group R\bar 3m (No. 166). The high-temperature modification crystallizes as an anti-type to Li(5)Ga(4), space group P\bar 3m1 (No. 164). Two polymorphs can be described as derivative structures to binary Li(5)Ga(4), Li(5)Sn(2), Li(13)Sn(5), Li(8)Pb(3), CeCd(2) and CdI(2) phases which belong to class 2 with the parent W-type in Krypyakevichs classification. All atoms in both polymorphs are coordinated by rhombic dodecahedra (coordination number CN = 14) like atoms in related structures. The Li(2)Zn(2.76) (for the low-temperature phase) and Li(2)Zn(2.82) (for the high-temperature phase) compositions were obtained after structure refinements. According to electronic structure calculations using the tight-binding-linear muffin-tin orbital-atomic spheres approximations (TB-LMTO-ASA) method, strong covalent Sn-Sn and Ga-Ga interactions were established in Li(5)Sn(2) and Li(5)Ga(4), but no similar Zn-Zn interactions were observed in Li(2)Zn(3).

Ce20Mg19Zn81: a new structure type with a giant cubic cell

Icosacerium nonadecamagnesium henoctacontazinc, Ce(20)Mg(19)Zn(81), synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F\overline{4}3m, a = 21.1979 (8) A] and represents a new structure type among the technologically important family of ternary rare earth-transition metal-magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have \overline{4}3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce(20)Mg(19)Zn(81) structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+Zn(4)+Zn(4)+Zn(12)+Ce(6)), B (Mg+Zn(12)+Ce(4)+Zn(24)+Ce(4)), C (Zn(4)+Zn(12)+Mg(6)) and D (Zn(4)+Zn(4)+Mg(12)+Ce(6)), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic-type bonding.

Crystal structure of the compound Ce7Pd4Ge2

Abstract The crystal structure of the compound Ce 7 Pd 4 Ge 2 has been determined by X-ray analysis of a single crystal (Dartch autodiffractometer, Mo Kα radiation, 1116 independent reflections, reliability factor R = 0.0491 in the anisotropic approximation). This structure has been found to belong to a new structural type: space group P2 1 /n, a = 9.315(2) A , b = 12.277(7) A , c = 12.698(3) A , β = 114.31(2)° , Z = 4. The coordination polyhedra of the cerium atoms have 15 and 17 apexes, those of palladium are trigonal prisms with three additional atoms and a tetragonal antiprism with one additional atom, and those of germanium are trigonal prisms with three additional atoms.