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The intermetallic Al5Co2 is defined as a structurally complex material and is considered a low-order quasicrystalline approximant. A single crystal of Al5Co2(001) was obtained by the Czochralski method. The sample was characterized by X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and X-ray photoelectron diffraction (PED). The surface composition was also analyzed by XPS, indicating only Al and Co compounds. In the current research, the crystal structure was qualitatively analyzed using the LEED patterns for different incident beam energies indicating a (1 × 1) termination, also in accordance with some literature works. The structure study was performed by applying the standard software MSCD and showed a (1 × 1) pattern. In addition, four different termination models for this termination were tested. The reliability factor indicated that the best termination belongs to the Al-rich surface layer. [ABSTRACT FROM AUTHOR]

We report on the dynamics of a magnetic-field-driven antiferromagnetic-to-paramagnetic quantum phase transition in monocrystalline Ce3Al via transverse-field muon spin rotation (TF-µSR) experiments down to low temperature of ∼ 80 mK. The quantum phase transition is of a spin-flip type and takes place on the Ce–Al magnetic chains as a result of competition between the indirect exchange and the Zeeman interaction of the Ce moments with the external field, applied along the chain direction (also the direction of the antiferromagnetic axis). The Ce moments are not static at T → 0, but fluctuate in their direction due to the Heisenberg uncertainty principle. Upon applying the magnetic field sweep, the fluctuations exhibit the largest amplitude at the quantum critical point, manifested in a maximum of the muon transverse relaxation rate at the critical field. The quantum nature of fluctuations observed in the TF-µSR experiments is reflected in the temperature independence of the average local magnetic field component along the external magnetic field at the muon stopping site(s) and the muon transverse relaxation rate within the investigated temperature range 1.5 K–80 mK. Quantum fluctuations are fast on the muon Larmor frequency scale, τ 0 < 10–10 s. [ABSTRACT FROM AUTHOR]

Complex intermetallic compounds such as transition metal (TM) aluminides are promising alternatives to expensive Pd-based catalysts, in particular for the semi-hydrogenation of alkynes or alkadienes. Here, we compare the gas-phase butadiene hydrogenation performances of o-Al13Co4(100), m-Al13Fe4(010) and m-Al13Ru4(010) surfaces, whose bulk terminated structural models exhibit similar cluster-like arrangements. Moreover, the effect of the surface orientation is assessed through a comparison between o-Al13Co4(100) and o-Al13Co4(010). As a result, the following room-temperature activity order is determined: Al13Co4(100) < Al13Co4(010) < Al13Ru4(010) < Al13Fe4(010). Moreover, Al13Co4(010) is found to be the most active surface at 110°C, and even more selective to butene (100%) than previously investigated Al13Fe4(010). DFT calculations show that the activity and selectivity results can be rationalized through the determination of butadiene and butene adsorption energies; in contrast, hydrogen adsorption energies do not scale with the catalytic activities. Moreover, the calculation of projected densities of states provides an insight into the Al13TM4 surface electronic structure. Isolating the TM active centers within the Al matrix induces a narrowing of the TM d-band, which leads to the high catalytic performances of Al13TM4 compounds. [ABSTRACT FROM AUTHOR]

Following the recent determination of the Al3AuIr structure, a new ternary phase has been identified in the Al–Au–Ir phase diagram. It has a chemical composition Al9(Au;Ir)4 with an apparently low gold content. Its crystal structure has been determined with single‐crystal X‐ray diffraction. The new compound crystallizes in the tetragonal crystal system and has been successfully solved in space group I41/acd (Pearson symbol tI104) with lattice parameters a = 8.6339 (2) and c = 21.8874 (7) Å. Atomic environments are described as well as similarities with the BGa8Ir4 compound. The discovery of a new Al–Au–Ir intermetallic compound is described; its crystal structure resolution is described and the Au/Ir mixed occupancy is discussed. [ABSTRACT FROM AUTHOR]

Recently, non-noble intermetallic compounds have shown promising catalytic performances in the partial hydrogenation of alkynes and alkenes. In this work, the properties of γ-Al4Cu9(1 1 0) toward the gas-phase hydrogenation of butadiene were investigated at total pressures of 2-20 mbar and temperatures of 110-180 °C. The model catalyst is active and 100 % selective to butenes. Moreover, although less active than Al13Fe4(0 1 0), which was evaluated previously for the same reaction, it is more selective and more stable. The combination of catalytic tests with pre- and postreaction Auger electron spectroscopy measurements and comparative tests with Cu(1 1 0) shows that Cu governs the reaction on γ-Al4Cu9(1 1 0). However, the lower activity of the (more Cu-rich) sputtered Al4Cu9 surface with respect to the annealed one and the differences between Al4Cu9 and Cu surfaces in terms of butene isomer distribution, butene conversion kinetics, and sensitivity to poisons, demonstrate the unique character of the intermetallic compound. [ABSTRACT FROM AUTHOR]

A new ternary phase with a composition of Al3AuIr has been found in the Al-rich area of the Al-Au-Ir system. Differential thermal analysis indicates a melting point of 990 °C, and single-crystal X-ray diffraction measurements reveal that this ternary phase adopts a Ni2Al3 structure type (space group P...m1) with a = 4.2584(5) Å and c = 5.1991(7) Å. This compound is isostructural to the Al3Cu1.5Co0.5 phase also found in the Al-rich part of the Al-Cu-Co ternary diagram. Experimental evidence combined with ab initio calculations point toward an Al3AuIr phase stabilized by a Hume-Rothery mechanism. Quantum chemical calculations indicate two-center and multicenter interactions in the Al3AuIr phase. Layered distribution of two-center interactions separated by regions with four- and five-center bonds suggests a preferential cleavage of the material at puckered planes perpendicular to the [001] direction. [ABSTRACT FROM AUTHOR]

For the first time, to the best of our knowledge, a realistic approach for deriving an estimate by superior values of the surface energy of complex metallic alloys based on aluminium is proposed. It turns out that the surface energy of quasicrystals lies in the range 0.5–0.8 J/m2, in contrast to pure aluminium (1.15 J/m2) orλ-Al13Fe4(2.0 J/m2) andω-Al7Cu2Fe (2.2 J/m2) intermetallics. [ABSTRACT FROM AUTHOR]

The results of an investigation of the electronic structure of the valence band of various Al-based complex intermetallic alloys, carried out using the X-ray emission spectroscopy technique, are presented and discussed. It is shown that the electronic structure results from an interplay between covalency and repulsive interactions that contributes to the formation of a pseudo-gap at the Fermi level in the Al electronic distributions. [ABSTRACT FROM AUTHOR]