Sabine Haag

On the crystal structure of Ba8Ni6N7, a low valency nitridon1ccolate with infinite helical [Ni-N] zigzag chains

Abstract Ba8Ni6N7 was prepared from mixtures (pressed pellets) of BaNiN and Ba3N2 (molar ratio 1:1) at 800 °C under nitrogen. The crystal structure was determined by single-crystal X-ray diffraction ( C2 c ; a = 948.7(4) pm, b = 1657.8(6) pm, c = 1213.7(7) pm; β = 107.05(5)°; Z = 4). The rather complex new structure type is generated by distorted nitrogen coordination octahedra (NBa6, NBa4Ni2(cis) and NBa4Ni2(trans)) which share common edges as well as common corners. Barium is in a threefold (trig, planar) and a fourfold (distorted tetrahedral) nitrogen environment. Nickel (nearly linear coordination, N-Ni-N angle: 162.4(5)°–176.4(4)dg) and nitrogen (distance Ni[2]-N[6]: 175.6(10)–181.0(14) pm) are arranged to form infinite helical [Ni-N] zigzag chains which run parallel to the c ∗ direction.

Ternäre Nitride des Lithiums mit den Elementen Cr, Mo und W / Ternary Lithium Nitrides with Elements Cr, Mo and W

The ternary compounds were prepared by reaction of the transition metals with Li3N melt under nitrogen. The crystal structures of Li6MeN4 (P42/nmc, Z = 2; Me = Mo: a = 667.3(1) pm, c = 492.5(3) pm; Me = W: a = 667.9(1) pm, c = 492.7(1) pm) and Li15Cr2N9 (P4/ncc, Z = 4; a = 1023.3(5) pm, c = 938.9(7) pm) can be described as fluorite-type superstructures with the lithium and transition metal atoms in tetrahedral holes of the nearly fcc nitrogen arrangement and with an ordered distribution of defects within the cation substructure. In addition, the ternary system Li–Cr–N contains the compound Li6CrN4 with a crystal structure which is not quite clear at present, but which shows close relations to the structures of Li6MeN4 (Me = Mo, W). The previously reported compounds Li9MeN5 (Me = Cr, Mo, W) have not been observed during this study. The respective Cr compound in fact is a nitride-oxide (nitride-imide) of composition Li14Cr2N8(O,NH) with a crystal structure (P3̄, Z = 1, a = 579.9(1) pm, c = 826.3(6) pm) also showing a fluorite-type superstructure.

The filamentary growth of metals

Abstract One-dimensional structures are starting to have impact in modern technological device design. A brief history of the fabrication of metal structures in such geometries is presented. At the dawn of modern science, in 1574, a recipe was published for the formation of “metallic grass”. This ancient recipe is reintroduced into modern technology using physical vapor deposition techniques to grow nanowhiskers. Defects in dewetting layers on various substrates are proven to act as nucleation sites for the whisker growth. This general approach is shown for Cu, Ag and Co nanostructures. The whiskers are of perfect crystal structure, devoid of defects and flaws and freestanding on the substrates. A phenomenological but energetically justified growth model is presented. The unique mechanical stability of these structures is shown by bending experiments. The theoretical limit of the mechanical strength is reached reproducibly.

Concentration and Strain Fields inside a Ag/Au Core-Shell Nanowire Studied by Coherent X-ray Diffraction

Three-dimensional coherent diffraction patterns of an isolated, single-crystalline Ag/Au core-shell nanowire were recorded at different X-ray beam energies close to the Au LIII absorption edge. Two-dimensional slices of the three-dimensional diffraction pattern, with the diffraction vector oriented perpendicular to the wire axis, were investigated in detail. In reciprocal space, facet streaks with thickness fringes were clearly observed in the two-dimensional diffraction patterns, from which the shape and size of the corresponding cross sections of the nanowire could be revealed. Comparison with simulated diffraction patterns exhibited the coherency strain field in the nanowire. During in situ annealing at temperatures which would lead to significant intermixing by volume diffusion in bulk material, according to literature data, a core-shell morphology was preserved; that is, intermixing in the nanowire was pronouncedly decelerated compared to bulk diffusion.