Crystal structure of incommensurate ηʺ-Cu1.235Sn intermetallic

The crystallographic parameters of the incommensurately ordered phase ηʺ of the composition Cu1.235Sn are reported. This phase belongs to the group of ordered Ni2In/NiAs-type phases, with a NiAs-type arrangement Cu(1)Sn and additional Cu(2) atoms partially occupying trigonal-bipyramidal interstices in an ordered fashion, leading to the formula Cu(1)Cu(2)0.235Sn = Cu1.235Sn. The structure model, afterward refined on the basis of powder X-ray diffraction data, has been derived on the basis of the slightly Cu-poorer commensurately ordered η′-Cu6Sn5 (=Cu1.2Sn) phase but also on previously reported commensurate structure models η8-Cu1.25Sn and η4+1-Cu1.243Sn derived from selected area electron diffraction data. In line with a recent work (Leineweber, Wieser & Hügel, Scr. Mater. 2020, 183, 66–70), the incommensurate ηʺ phase is regarded as a metastable phase formed upon partitionless ordering of the η high-temperature phase with absent long-range ordering of the Cu(2) atoms. The previously described η8 and η4+1 superstructure are actually of the same phase, and the corresponding superstructure models can be regarded as approximant structures of the ηʺ phase.The refined structure model is described in 3+1 dimensional superspace group symmetry C2/c(q10-q3)00 with a unit cell of the average structure with lattice parameters of aav = 4.21866(3) Å, bav = 7.31425(5) Å, cav = 5.11137(3) Å and bav = 90.2205(5)° and a unit cell volume V = 157.717(2) Å3. The modulation vector is with q1 = 0.76390(4), q3 = 1.51135(5), and governs the spatial modulation of the occupancy of the Cu(2) atoms described by a Crenel function. The occupational ordering is accompanied by displacive modulations of the atoms constituting the crystal structure, ensuring reasonable interatomic distances on a local level. In particular, the spatial requirements of pairs of edge-sharing Cu(2)Sn5 trigonal bipyramids (Cu(2)2Sn8) lead to a measurable splitting of some fundamental reflections in the powder diffraction data. This splitting is considerable smaller in η′-Cu1.20Sn, which lacks such pairs due to the lower Cu content.

Metal-rich tellurides PdTe1−xBix as functional materials: Catalytic behavior in the Fischer–Tropsch synthesis and bonding analysis

A series of solid solutions in the PdTe–PdBi system with general formula [Formula: see text]Bix ([Formula: see text], 0.5, 0.67) with the structure based on the NiAs type were synthesized by a high-temperature ampoule technique. These compounds, along with their parent binaries, PdTe and PdBi, were tested as promoters for the standard Co/Al2O3 catalytic system in the Fischer–Tropsch synthesis. It is shown that the addition of PdTe and [Formula: see text]Bix to the standard catalyst increases both yield and selectivity with respect to the liquid phase. At the same time, the addition of PdBi does not only improve catalytic activity, but also slightly inhibits it. Another positive effect of the PdTe and [Formula: see text]Bix addition is the shift in the conversion products toward the diesel and wax fractions. Chemical bonding analysis in orbital and direct space indicates that the addition of Bi to PdTe might increase the localized bonding.

Ultrastable lithium–sulfur batteries with outstanding rate capability boosted by NiAs-type vanadium sulfides

A new type of vanadium sulfide (V2S3) was used for high-performance lithium–sulfur batteries.

Stability and magnetism of FeN high-pressure phases

We have studied the formation and stability of high-pressure iron mono-nitride phases, and in particular a new magnetic phase with a NiAs-type structure.