Tim Dinges

Lithium-Transition Metal-Tetrelides – Structure and Lithium Mobility

Abstract Lithium-transition metal (T)-tetrelides (tetr.= C, Si, Ge, Sn, Pb) are an interesting class of materials with greatly differing crystal structures. The transition metal and tetrel atoms build up covalently bonded networks which leave cavities or channels for the lithium atoms. Depending on the bonding of the lithium atoms to the polyanionic network one observes mobility of the lithium atoms. The crystal chemistry, chemical bonding, 7Li solid state NMR, and the electrochemical behavior of the tetrelides are reviewed herein.

Synthesis and structure of Li8Rh7Sn8 and Li1.23Rh1.77Sn

Abstract The stannides Li8Rh7Sn8 and Li1.23Rh1.77Sn were synthesized from the elements in sealed niobium ampoules. The structures were refined on the basis of single crystal X-ray diffractometer data: MnCu2Al type (Heusler phase), Fm-3m, a = 615.5(4) pm, wR2 = 0.0319, 106F2 values, 6 variables for Li1.23Rh1.77Sn and P-3m1, a = 894.4(4) pm, c = 1107.3(4) pm, wR2 = 0.0600, 1287F2 values, 48 variables for Li8Rh7Sn8 which crystallizes with a new structure type. The rhodium site in Li1.23Rh1.77Sn shows Rh/Li mixing. The structure of Li8Rh7Sn8 contains two pronounced structural motifs. Layers of edge-sharing RhSn6 octahedra alternate with layers of six-membered rings of corner-sharing SnRh4 tetrahedra in UDUDUD orientation. The [Rh7Sn8]δ– polyanionic network is characterized by covalent rhodium-tin bonding.

Growth of NaBr in the 5-5 Structure Type on LiNbO3: A Feasibility Study

The feasibility of growing alkali halides in the hypothetical 5-5 structure type on a specially prepared substrate of LiNbO3 has been investigated. The highest degree of steering towards this structure is achieved by growing NaBr on a LiNbO3 (001)-surface, where the outermost layer of oxygen atoms is followed by a layer of niobium atoms. The kinetic stability, against transition into the rock salt structure, of the 5-5 structure grown on the substrate is enhanced compared to the bulk 5-5 phase, but the 5-5 structure will nevertheless still be metastable compared to the rock salt structure type that constitutes the thermodynamically stable bulk phase of NaBr under standard conditions

Li13.7Rh8Si18.3 – A Non-Centrosymmetric Variant of the R-Phase Structure

The silicide Li13.7Rh8Si18.3 was synthesized from the elements in a sealed niobium ampoule at 1370 K followed by slow cooling. The sample was studied by powder and single-crystal X-ray diffraction. Li13.7Rh8Si18.3 crystallizes with a non-centrosymmetric occupancy variant of the R-phase structureMg32( Al, Zn)49: I23, a = 1306.9(2) pm, wR2 = 0.0447, 1286 F2 values, and 53 variables. Striking structural motifs of the Li13.7Rh8Si18.3 structure are M12 icosahedra and M60 buckyball-type clusters (M = Si + Rh), both partially built up from mixed-occupied sites. Graphical Abstract Li13.7Rh8Si18.3 – A Non-Centrosymmetric Variant of the R-Phase Structure

TaRhGe with TiNiSi-type Structure

The new germanide TaRhGe was prepared from the elements by arc-melting and subsequent annealing at 1020 K for 10 days. TaRhGe crystallizes with the TiNiSi-type structure, space group Pnma, Z = 4, oP12, a = 640.2(2), b = 383.2(2), c = 741.7(2) pm, wR2 = 0.0550, 432 F2 values, 20 parameters. The structure consists of a three-dimensional [RhGe] network of distorted RhGe4/4 tetrahedra with Rh-Ge distances ranging from 244 to 250 pm. The tantalum atoms are coordinated within this network by two folded and mutually tilted Rh3Ge3 hexagons. TaRhGe is Pauli-paramagnetic and shows no superconducting transition down to 3 K Graphical Abstract TaRhGe with TiNiSi-type Structure