Search

The novel composition – TiFe1.3Os3.9B2.8 – is the first quaternary phase of the NbRuB structure type. The layer‐like structure consists of boron (mixed with 8 % Fe) dumbbells in the same layer as osmium atoms, some sites with mixed occupancies. The second layer has isolated boron, osmium/titanium (51 % Os) and iron atoms. The presence of iron enables the study of magnetism as Fe‐chains are present, with intra‐ and interchain distances of 3.02 Å and 5.76 Å, respectively. Density functional theory (DFT) predicts magnetic ordering to be likely with the antiferromagnetic ground state only 13 meV more favorable than the ferromagnetic state. This discovery opens the possibilities of studying various quaternary compositions in the superconducting NbRuB structure type. [ABSTRACT FROM AUTHOR]

Polycrystalline samples and single crystals of the new metal-rich boride V1+ xNb1- xIrB2 ( x ≈ 0.1), were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-ray diffraction and EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase adopts the Mo2IrB2-type structure (space group Pnnm, no. 58) with the lattice parameters a = 7.301(7) Å, b = 9.388(9) Å and c = 3.206(5) Å. It is the first quaternary representative of Mo2IrB2-type structure. The structure contains zigzag B4-fragments with boron-boron distances of 1.83-1.85 Å. The electronic density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron-boron interactions are observed in the zigzag B4-fragment and two significantly different Ir-B interactions are observed in the new phase and the prototype Mo2IrB2. [ABSTRACT FROM AUTHOR]

We present the first bulk synthesis of Ti3Co5B2, which was realized by arc-melting a Co-rich elemental mixture. Our X-ray diffraction studies revealed a Ti/Co mixed occupancy on one of two possible Ti sites suggesting a phase width with x = 0-0.52 in Ti3- xCo5+ xB2. Moreover, we studied experimentally and theoretically the isoelectronic substitution of Ti and Co by their respective higher homologues (Zr/Rh and Hf/Ir). Surprisingly, Ti3Co5B2-type phase was obtained only for the Hf/Ir combination (single crystal analysis of Hf3Ir5B2), whereas for Zr/Rh a perovskite-like phase (ZrRh3Bx) was discovered instead. We found that small but crucial differences (atomic radius ratio and electronegativity difference) between elements of the same group in the periodic Table are responsible for the unexpected trend deviation. This finding is supported by DFT calculations of the free energy of formation. [ABSTRACT FROM AUTHOR]

Recent research on van der Waals (vdW) metal chalcogenides electrocatalysts for the hydrogen evolution reaction (HER) has been devoted to finding new catalysts with active basal planes. Here, we report on experimental and theoretical investigations of the HER activity of a recently discovered iron‐rich vdW spintronic material, Fe5Ge2Te2 (FG2T) in alkaline media (1 M KOH). We show that a densified electrode of FG2T requires an overpotential of only −90.5 mV to drive a current density of 10 mA/cm2. Free energy calculations of hydrogen adsorption using density functional theory (DFT) proved that the numerous sites present on the hexagonal Te layer are more active than those found in the recently proposed Fe3GeTe2 (FGT) catalyst, supporting higher activity for the new Fe‐richer catalyst. Like in FGT, XPS analysis has found that a thin oxide layer covers the active FG2T layers, suggesting the real active surface to be a hybrid FG2T/oxide layer. These results strengthen the idea of continued screening of iron‐based vdW materials to replace the non‐abundant platinum group electrocatalysts toward HER and other electrocatalytic processes. [ABSTRACT FROM AUTHOR]

The intermetallic compound CaAu2Al2, and the members of the solid solutions SrAu2- xAl2+ x (0 ≤ x ≤ 0.33) and Ba3Au5+ xAl6- x ( x = 0, 0.14, 0.49) were synthesized from the elements in sealed tantalum ampoules. The Ca compound crystallizes with the orthorhombic ThRu2P2 type structure, whereas the targeted SrAu2Al2 was found to form a solid solution according to SrAu2- xAl2+ x. For the Ba system no 'BaAu2Al2' was found, however, Ba3Au5+ xAl6- x was discovered to crystallize in the monoclinic space group C2/ c with its own structure type. The samples were investigated by powder X-ray diffraction and their crystal structures were refined on the basis of single-crystal X-ray diffraction data. All compounds were characterized furthermore by susceptibility measurements. The crystallographic aluminum sites of CaAu2Al2 and Ba3Au5Al6 can be differentiated by 27Al solid state NMR spectra on the basis of their different electric field gradients, in agreement with theoretical calculations. The electron transfer from the alkaline earth metals and the aluminum atoms onto the gold atoms was investigated by X-ray photoelectron spectroscopy (XPS) classifying these intermetallics as aurides, in full agreement with the calculated Bader charges. [ABSTRACT FROM AUTHOR]