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Semiconducting SnSe, an analog of black phosphorus, recently attracted great scientific interest due to a disputed report of a large thermoelectric figure of merit, which has not been reproduced subsequently. Here we concentrate on the low-temperature ground state. To gain a better understanding of the system, we present magneto-transport properties in high-quality single crystals of as-grown, lightly doped SnSe down to liquid helium temperatures. We show that SnSe behaves as a p-type doped semiconductor in the vicinity of a metal-insulator transition. Electronic transport at the lowest temperatures is dominated by the hopping mechanism. Negative magnetoresistance at low fields is well described by antilocalization, while positive magnetoresistance at higher fields is consistent with the shrinkage of localized impurity wavefunctions. At higher temperatures, a dilute metallic regime is realized where elusive T2 and B2 resistivity dependence is observed, posing a challenge to theoretical comprehension of the underlying physical mechanism.

The unfilled skutterudite ${\mathrm{CoSb}}_{3}$ is a small-gap semiconductor which was predicted to be close to a strain-induced transition to a topological-insulator phase passing through a topological quantum critical point. As a starting point to strain measurements, the aim of this work is to characterize the electronic structure of as-grown samples. Two types of samples, one grown in Sb flux and the other by an inclined rotary Bridgman technique, are compared based on structural properties, resistivity, Hall effect, and magnetization. All samples appear metallic with small growth-dependent hole doping. Measurements of quantum oscillations in magnetization and angle-dependent electronic transport confirm the calculated band structure at ambient pressure. The Fermi surface consists of a single spherical sheet at the $\mathrm{\ensuremath{\Gamma}}$ point, and the purest samples grown by the Bridgman technique have a Fermi energy lying 25 meV below the valence-band edge. Band-structure calculations provide an accurate description of the experimental results. Hence, this compound is suitable for an investigation of topological states under strain.

Combining inelastic neutron and x-ray scattering with atomic scale simulation, we report on a comprehensive study of the lattice dynamics and its relationship with the low thermal conductivity of the o-${\mathrm{Al}}_{13}{\mathrm{Co}}_{4}$ phase, a periodic approximant (about 100 atoms per cell) to a decagonal quasicrystal. The obtained experimental data, phonon lifetimes, and temperature-independent lattice thermal conductivity can only be fully described by molecular dynamics simulations, using oscillating pair potential, when the disorder of 12 Al sites is properly taken into account. Our results pave the way for a detailed understanding of materials where structural complexity and local disorder are at play.

The crystal structure of the complex intermetallic phase o-Al13Co4 was first investigated in 1994, but some open questions still remained. The new refinement of the crystal structure using high-resolution X-ray diffraction data resulted in a much more complex model including a large number of split positions (space group Pnm21, a = 8.1590(6) Å, b = 12.349(1) Å, c = 14.453(1) Å). The model is interpreted in terms of local violation of the translational symmetry, which is confirmed by HRTEM and HRSTEM investigations. Chemical bonding between two partial structures in o-Al13Co4 - three-dimensional framework and linear Co–Al–Co groups in cages of the latter – along with the stacking faults (local twinning) are discussed as possible reasons for such an extended disorder. Previous article in issue

The intermetallic phase FeGa3 belongs to the rare examples of substances with transition metals where semiconducting behavior is found. The necessary electron count of 17 ve/fu can be formally derived from eight Fe-Ga and one Fe-Fe two-center-two-electron bond. The situation is reminiscent of the well-known Fe2(CO)9 scenario, where a direct Fe-Fe two-center-two-electron bond was shown to not be present. Fe-Fe interaction in FeGa3 and its substitution variants represents the crucial point for explanation of electronic, thermal transport, and optical properties of this material. Chemical bonding analysis in position space of FeGa3 and Fe2(CO)9 on the basis of the topology of the electron localizability indicator distribution, QTAIM atoms, two- and three-center delocalization indices, domain natural orbitals, IQA analysis, and an evaluation of the Fe-Fe dissociation energy yields a complete picture of the partially compensated Fe-Fe bond, which is nevertheless strong enough to be of decisive importance. Structural reinvestigation of differently synthesized single crystals leads to the composition Fe1+ xGa3 (0 ≤ x ≤ 0.018), where the additional Fe atoms are predicted from DFT/PBE calculations to yield a magnetic moment of about 2 μB/Fe2 atom and metallic in-gap states. Accompanying magnetization and ESR measurements are consistent with this picture.

The atomic structure of a 0.2 atom % Pt-doped complex metallic alloy, monoclinic Al13Fe4, was investigated using a single crystal prepared by the Czochralski method. High-angle annular dark-field scanning transmission electron microscopy showed that the Pt atoms were dispersed as single atoms and substituted at Fe sites in Al13Fe4. Single-crystal X-ray structural analysis revealed that the Pt atoms preferentially substitute at Fe(1). Unlike those that have been reported, Pt single atoms in the surface layers showed lower activity and selectivity than those of Al2Pt and bulk Pt for propyne hydrogenation, indicating that the active state of a given single-atom Pt site is strongly dominated by the bonding to surrounding Al atoms.

Sb-based compounds such as CoSb 3 and FeSb 2 are interesting materials for thermoelectric applications. Their single crystal growth can be achieved from high-temperature solutions that are strongly enriched in Sb. In Bridgman growth using closed ampoules, effective mixing of the solution is an important prerequisite in order to minimize the high risk of liquid inclusion formation. We have successfully grown inclusion-free single crystal of CoSb 3 and FeSb 2 by rotating the ampoule in a Bridgman-type crystal growth set-up being inclined by 75° with respect to the vector of gravity. Numerical modelling as well as experimental growth studies have demonstrated the strong influence of forced convection that is achieved by this modified directional solidification technique called Inclined Rotary Bridgman method.

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., Graphical abstract

Intermetallic compounds have proved to be interesting alternatives to heterogeneous catalysts prepared from pure noble metals or their alloys. As to study their intrinsic properties, to determine the crystalline structures of specific surfaces and finally to understand elementary processes of heterogeneous catalysis, single crystals of these intermetallics are needed. Inspired by the recent discovery of Ga–Ni catalysts for carbon dioxide reduction to methanol, we have grown for the first time cm3-size single crystals of trigonal Ga3Ni2. We report in detail on the synthesis and Czochralski growth from high-temperature solution using Ga as native solvent. Inclusion formation of Ga-rich fluid proved to be the most severe problem that was minimized by using an extremely low pulling rate down to 25 µm/h.

In order to obtain the local charge disturbance around substituted Ge atom in a prototype system of ferromagnetic quantum criticality, FeGa3−xGex, we have measured 69,71Ga Nuclear Quadrupole Resona...

Intermetallic compounds in the binary Ga-Pd system have proved to be superior as catalysts in the semi-hydrogenation of acetylene. Partial substitution of Ga by Sn even increases the activity. In order to study elementary processes of catalytic reactions, well-oriented surfaces of single-crystalline slaps are needed, i.e. single crystal growth is a prerequisite. For the first time, solid/liquid equilibria including the solid solutions Ga1−xSnxPd and Ga1−xSnxPd2 were studied. Based on these findings single crystal growth of the two solid solution series succeeded using the Czochralski method from (Ga,Sn)-rich solutions. Inclusion-free single crystals of a few cm3 in size could be obtained. Due to different crystal structures of the end members, Sn substitution in Ga1−xSnxPd is restricted to x ≈ 0.15 in the cubic phase. Although a complete solid solution range for Ga1−xSnxPd2 has been reported by Armbruster et al. (2018), mixed crystals of the 1:2 phase can be grown from a native ternary melt only up to approx. x = 0.54 due to missing solid/liquid equilibria at a higher ratio of Sn substitution for Ga.

The intermetallic phase FeGa

Background In a routine handling of a catalyst material, exposure to air can usually not be avoided. For noble metal catalysts that are resistant to oxidation, this is not an issue, but becomes important for intermetallic catalysts composed of two or more non-noble chemical elements that possess much different standard enthalpies of the oxide formation. The element with higher affinity to oxygen concentrates on the surface in the oxide form, whereas the element with lower affinity sinks into the subsurface region. This changes the number of active sites and the catalytic performance of the catalyst. We have investigated the instability of the surface composition to oxidation of the Ga3Ni2 noble metal-free intermetallic compound, a new catalyst for the CO2 reduction to CO, CH4 and methanol. Methods The instability of the oxidized Ga3Ni2 surface composition to different heating–annealing conditions was studied by X-ray photoelectron spectroscopy (XPS), used to determine the elemental composition and the chemical bonding in the near-surface region. The dispersion of active sites available for the chemisorption of H2 and CO on the Ga3Ni2 catalyst surface was determined by H2 and CO temperature-programmed desorption. CO2 conversion experiments were performed by using the catalyst material reduced in hydrogen at temperatures of 300 and 600 °C. Results XPS study of the Ga3Ni2 surface subjected to different heating–annealing conditions has revealed that the concentration of Ga at the oxidized surface is strongly enhanced and the concentration of Ni is strongly depleted with respect to the values in the bulk. By annealing the surface at 600 °C in ultra-high vacuum, the oxides have evaporated and thermal diffusion of atoms near the surface has partially reconstructed the surface composition towards the energetically more favorable bulk value, whereas annealing at a lower temperature of 300 °C was ineffective to change the surface composition. Catalytic tests were in agreement with the XPS results, where an increased CO2 conversion for the catalyst reduced with hydrogen at a higher temperature followed an increased Ni/Ga surface concentration ratio. Conclusions The instability of the active surface chemical composition to oxidation in air must be taken into account when considering noble metal-free intermetallic catalysts as alternatives to the conventional catalysts based on noble metals. Ga3Ni2 and other Ga–Ni intermetallic compounds are good examples of binary intermetallic catalysts, whose catalytic performance is strongly affected by exposure to the air.

The atomic structure of a 0.2 atom % Pt-doped complex metallic alloy, monoclinic Al

Intermetallic compound GaPd 2 is a highly selective catalyst material for the semi-hydrogenation of acetylene. We have determined anisotropic electronic, thermal and magnetic properties of a GaPd 2 monocrystal along three orthogonal orthorhombic directions of the structure. By using 69 Ga and 71 Ga NMR spectroscopy, we have determined the electric-field-gradient tensor at the Ga site in the unit cell and the Knight shift, which yields the electronic density of states (DOS) at the Fermi energy e F . The DOS at e F was determined independently also from the specific heat. To see the change of electronic properties of the GaPd 2 phase on going from the bulk material to the nanoparticles morphology, we have synthesized GaPd 2 /SiO 2 supported nanoparticles and determined their electronic DOS at e F from the 71 Ga NMR spin-lattice relaxation rate. The electronic DOS of the GaPd 2 was also studied theoretically from first principles. All results are compared to the chemically related compound GaPd. The active–site-isolation concept for an increased catalytic selectivity is discussed in relation to the GaPd 2 and GaPd structures.

International audience; We report the adsorption of lead adatoms on the pseudo-10-fold Al13Fe4(0 1 0) surface using low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). For the submonolayer regime, Pb adatoms remain highly mobile across the surface at 300K. STM analysis indicates the formation of irregularly shaped islands of monoatomic height. The latter do not coalesce with increasing coverage. At 0.95 MLE coverage, the LEED patterns are consistent with a pseudomorphic growth of the adatoms. This is confirmed by STM measurements which reveal local motifs qualitatively similar to those observed on the clean Al13Fe4(0 1 0) surface, i.e. prior to dosing. Apart from the absence of plasmons, the XPS measurements of Pb 4f and Al 2s core levels are comparable to those observed for the Pb/Al(1 1 1) system.

The intermetallic semiconductor FeGa

The atomic structure of the Al13Ru4(010) approximant surface, investigated for annealing temperatures ranging from 873 K to 1143 K, can be described by pentagonal motifs and vacancies. It exhibits an atypical surface reconstruction which manifests itself in real space by well-separated stripes running about 10○ off the [001] direction. Their mutual ordering is drastically improving at high annealing temperature. This is simultaneously accompanied by a filling of the pentagonal hollow sites present in the stripes with atoms or groups of atoms. We provide evidence that these unidirectional features are of true surface origin. The bulk electronic density of states calculated within the density functional theory framework matches the experimental valence band spectra. In addition to step edges, molecular adsorption reveals that stripes are initially the most reactive sites, leading to anisotropic island growth.

The intermetallic semiconductor FeGa$_{3}$ acquires itinerant ferromagnetism upon electron doping by a partial replacement of Ga with Ge. We studied the electron spin resonance (ESR) of high-quality single crystals of FeGa$_{3-x}$Ge$_x$ for $x$ from 0 up to 0.162 where ferromagnetic order is observed. For $x = 0$ we observed a well-defined ESR signal, indicating the presence of pre-formed magnetic moments in the semiconducting phase. Upon Ge doping the occurrence of itinerant magnetism clearly affects the ESR properties below $\approx 40$~K whereas at higher temperatures an ESR signal as seen in FeGa$_{3}$ prevails independent on the Ge-content. The present results show that the ESR of FeGa$_{3-x}$Ge$_x$ is an appropriate and direct tool to investigate the evolution of 3d-based itinerant magnetism., Comment: 12 pages, 7 figures

Thermoelectric materials as energy harvesters are a hot spot in research community due to their ability to directly convert waste heat into electrical energy. The efficiency of thermoelectric materials is determined by the dimensionless figure of merit ZT. For high thermoelectric conversion efficiency large Seebeck coefficient, large electrical conductivity and low thermal conductivity are required. Unfortunately, last two requirements are often hard to realize simultaneously in the same material because charge carriers usually carry heat efficiently as well. Thus systems with relatively low charge carrier concentration are usually good thermoelectrics. In those systems phonons are dominant heat conducting channel and their contribution can be further reduced through material architecturing. But, it was recently reported that SnSe in single crystalline form, exhibits high thermoelectric figure of merit (2.6 at 973 K) mainly due to its intrinsic extremely low thermal conductivity [1]. This makes SnSe one of the most promising thermoelectric materials. Although physical properties of SnSe above room temperature are well investigated, there are very few studies of low-temperature single-crystalline phase [2]. Motivated to determine the possible origins of these remarkable properties, we measured thermoelectric properties of SnSe down to low temperatures. Here we present investigation of anisotropic thermoelectric transport properties of SnSe at low temperatures, along the three crystallographic directions. We find that the thermal conductivity features a pronounced umklapp maximum near 12K. Our results indicate that the lattice thermal conductivity of single-crystalline SnSe at room temperature is higher than this reported in the literature [1]. We further discuss possible reasons for the differences observed between our results and those previously obtained by Zhao et al. [1]. Wei et al. have reported that the lower densities of the samples measured by Zhao et al. (5.4 g/cm3) may be correlated with the lower thermal conductivity values of their samples (our sample density is close to theoretical density of 6.18 g/cm3) [3]. This implies that their reported thermal conductivities are not intrinsic to high quality SnSe single crystal. Possible routes for optimizing low- temperature thermoelectric efficiency will be discussed. [1] Zhao, L. D., Lo, S. H., Zhang, Y., Sun, H., Tan, G., Uher, C., Wolverton, C., Dravid, V. P., Kanatzidis, M. G. (2014). Nature 508, 373. [2] Ibrahim, D., Vaney, J.-B., Sassi, S., Candolfi, C., Ohorodniichuk, V., Levinsky, P., Semprimoschnig, C., Dauscher A., Lenoir, B. (2017). Appl. Phys. Lett. 110, 032103. [3] Wei, P.C., Bhattacharya, S., He, J., Neeleshwar, S., Podila, R., Chen, Y.Y., Rao, A. M. (2016). Nature 539, E1-E2.

Quite recently intermetallic compounds have been investigated as catalysts for heterogeneous catalysis as they can be highly active regarding a specific reaction and often show advantages in selectivity and long-term stability. The intermetallic phase InPd (CsCl structure type) is considered to be a possible catalyst for methanol steam reforming. Single crystals are needed to study the basic processes of catalysis. Using the Czochralski technique, InPd single crystals were grown from In-rich solutions as to reduce the vapor pressure of In. The crystals show some unusual rough surface morphology and gradients concerning the main components composition. By adjusting the growth parameters like growth temperature and growth rate we succeeded to get inclusion-free single crystals.

Single crystal growth of the intermetallic compounds GaPd 2 , GaPd, and Ga 7 Pd 3 is described for the first time. These phases have recently been explored as highly selective heterogeneous catalysts in the semi-hydrogenation of acetylene. Well-oriented single-crystalline surfaces are needed to perform fundamental studies on catalytic processes. The three Ga–Pd phases were grown using the Czochralski method from Ga-rich solutions. Thermodynamic properties of the Ga–Pd system determine very different growth temperatures reaching from less than 460 °C for Ga 7 Pd 3 to about 1200 °C for GaPd 2 . Avoiding mother liquid inclusion formation proved to be the key problem that could be solved by pulling rates sometimes as low as 25 µm/h and forced convection by high crystal rotation rates. In the last grown part of GaPd 2 crystals decomposition into GaPd 2 /Ga 3 Pd 5 lamellas occurred which can be explained either by spinodal decomposition or by nucleation caused by the GaPd 2 stability region that becomes narrower with decreasing temperatures.

Two symmetrically nonequivalent silicon carbide (SiC) substrate orientations, (0001) Si-terminated and $$(000\overline{1} )$$ C-terminated, were used in the physical vapour transport growth of bulk aluminium nitride (AlN) single crystals. The crystals grown on Si-faces always exhibit an Al-polar growth surface. AlN growth on $$(000\overline{1} )$$ C-terminated surfaces of the SiC substrates was performed to obtain N-polar growth surfaces. An abrupt interface was observed between the AlN crystal and the C-face substrate which is in contrast to the growth on Si-faces where hexagonally shaped SiC hillocks are formed. The growth on C-faces is usually dominated by multi-site nucleation. Applying similar supersaturation conditions that led to step-flow growth on Si-faces to the C-faces resulted in a spiral growth mode, even on highly off-oriented substrates. The obtained broad X-ray diffraction rocking curves of such samples (full-width at half-maximum ≈380 arcsec) indicate the presence of more misfit dislocations and significant misfit stress. In addition, polarity inversion is observed in C-face grown crystals. Though the structural properties of the crystals grown on C-face are inferior to that of the crystals grown on Si-face, the incorporation of unintentional Si impurity was found to be lower (

The atomic structure and composition of a catalyst's surface have a major influence on its performance regarding activity and selectivity. In this respect, intermetallic compounds are promising future catalyst materials, as their surfaces exhibit small and well-defined ensembles of active metal atoms. In this study, the active adsorption sites of the 3-fold-symmetric surfaces of the PdGa interrnetallic compound were investigated in a combined experimental and computational approach using CO as a test molecule. The PdGa(111) and (-1-1-1) surfaces exhibit very similar electronic structures, but have Pd sites with very different, well-defined atomic coordination and separation. They thereby serve as prototypical model systems for studying ensemble effects on bimetallic catalytic surfaces. Scanning tunneling microscopy and Fourier transform infrared spectroscopy show that the CO adsorption on both surfaces is solely associated with the topmost Pd atoms and Ga acts only as an inactive spacer. The different local configurations of these Pd atoms dictate the CO adsorption sites as a function of coverage. The experimental results are corroborated by density functional theory and illustrate the site separation and ensemble effects for molecular adsorption on intermetallic single crystalline surfaces.

Single crystal growth and characterization of the binary semiconducting compound FeGa3 and its Ge‐substitute FeGa3–xGex are reported. Whereas there have been several investigations on the thermoelectric properties based on small samples grown by the flux method, this study is the first approach using the Czochralski growth technique from well‐oriented single‐crystalline seeds. Problems and solutions of the growth of cm3‐size single crystals are discussed in detail. Ge segregation in FeGa3–xGex is described by a segregation coefficient lower than unity which leads to an axially increasing Ge content along the pulling direction. Consequences with respect to lattice parameter changes and thermoanalytic measurements are reported.

The single crystal deformation behaviour of orthorhombic Al13Co4 hasbeen studied below the brittle-ductile transition temperature observedin bulk material from room temperature to 600 degrees C, usingindentation, microcompression and transmission electron microscopy. Atroom temperature, slip occurred most easily by dislocation motion on the(0 0 1)[0 1 0] slip system, as observed in the ductile regime at hightemperatures. However, as the temperature was increased towards 600degrees C, the slip pattern changed to one consisting of linear defectsrunning perpendicular to the loading axis. Serrated flow was observed atall temperatures, although at 600 degrees C the magnitude of theserrations decreased. Anomalous yielding behaviour was also observedabove 226 degrees C, where both the yield and the 2\% flow stressincreased with temperature, almost doubling between 226 and 600 degreesC. It has been suggested that this might arise due to the increasingstability of orthorhombic Al13Co4 with respect to the monoclinic formwith increasing temperature. This is shown to be consistent with thetheoretical predictions that exist.

The oxidation of the Al4(Cr, Fe) quasicrystal approximant has been studied using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM data indicate that the initial oxidation on the (1 0 0) surface proceeds in a highly ordered fashion. Oxygen preferentially adsorbs onto the surface of terraces, and step edges remain intact. The STM images show ordered stripes after initial oxidation. XPS data indicate that only Al is oxidised, with at least two oxidation states present. The Cr and Fe peaks remain unchanged. The oxidation of Al, rather than Cr or Fe, is consistent with the enthalpies of formation for each oxide. The stripes visible on the STM images are therefore identified to be the initial stages of aluminium oxide formation. XPS performed after higher O2 exposure indicates that the (1 0 0) termination shows hindered Al oxide film thickness growth rates compared to the (0 1 0) and (0 0 1) surfaces.

Czochralski growth of cm size decagonal AlCoNi single crystals from Al-rich high-temperature solutions is described using native seeds oriented parallel to all symmetrically different crystal directions. Morphological observations allow first hints with respect to anisotropic growth rates. But only classical detachment experiments according to the original idea of Jan Czochralski reveal quantitative results of kinetically limited growth rates. Geometric conditions of wetted plane interfaces as well as aspects of constitutional supercooling affect the detachment experiments. Thus, in only one specific orientation of the decagonal quasicrystal quantitative data for the maximum growth rate could be obtained.

A comprehensive study of the BaF2–Ba3(BO3)2 phase diagram has revealed a significant difference between the two intermediate phases Ba5(BO3)3F and Ba7(BO3)4−y F2+3y . The latter exhibited (BO3)3− ↔ 3F− anionic substitution which, unusually, strongly influences the solidus temperature. A comparison of the Ba5(BO3)3F and Ba7(BO3)4−y F2+3y crystal structures, along with consideration of other compounds demonstrating (BO3)3− ↔ 3F− isomorphism, allows for the disclosure of the mechanism of (BO3)3− ↔ 3F− heterovalent anionic substitution in fluoride borates via [(BO3)F]4− tetrahedral groups being replaced by four fluoride anions. No exception to this mechanism has been discovered among all known phases with (BO3)3− ↔ 3F− substitution.

$^{71}\mathrm{Ga}$ NQR, magnetization, and specific-heat measurements have been performed on polycrystalline Ge-doped ${\mathrm{FeGa}}_{3}$ samples. A crossover from an insulator to a correlated local moment metal in the low-doping regime and the evolution of itinerant ferromagnet upon further doping is found. For the nearly critical concentration at the threshold of ferromagnetic order, ${x}_{C}=0.15, ^{71}(1/{T}_{1}T)$ exhibits a pronounced ${T}^{\ensuremath{-}4/3}$ power law over two orders of magnitude in temperature, which indicates three-dimensional quantum critical ferromagnetic fluctuations. Furthermore, for the ordered $x=0.2$ sample (${T}_{C}\ensuremath{\approx}6$ K), $^{71}(1/{T}_{1}T)$ could be fitted well in the frame of Moriya's self-consistent renormalization theory for weakly ferromagnetic systems with $1/{T}_{1}T\ensuremath{\sim}\ensuremath{\chi}$. In contrast to this, the low-doping regime nicely displays local moment behavior where $1/{T}_{1}T\ensuremath{\sim}{\ensuremath{\chi}}^{2}$ is valid. For $T\ensuremath{\rightarrow}0$, the Sommerfeld ratio $\ensuremath{\gamma}=(C/T)$ is enhanced $(70\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/\mathrm{mole}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{2}$ for $x=0.1)$, which indicates the formation of heavy $3d$ electrons.

Magneto-transport properties of single crystal SnSe thermoelectric

Bulk AlN single crystals (3 mm thick and 1 in. diameter) were hetero-epitaxially grown on (0001) 6H–SiC substrates by the sublimation method. Double-crystal x-ray diffraction and micro-Raman results confirm the good crystallinity as well as structural homogeneity of the grown crystals. The presence of low-angle grain boundaries was observed by x-ray diffraction rocking curve analysis and also supported by defect-selective etching analysis. The estimated defect density of the 3 mm thick crystals is about (5–8)×10 5 cm −2 . 3D-microstructures with different morphology were observed on the as-grown crystal surfaces and were interpreted to be originated from screw dislocations. These screw dislocations are decorated by carbon impurities as evidenced by micro-Raman spectroscopic measurements. SiC incorporation in the grown crystals was found to be fairly low with 4 mol% at 2 mm distance from the interface and varies slightly between different sub-grains.

Scratching the surface: The high selectivity of PdGa catalysts towards the partial hydrogenation of acetylene was previously attributed to the separation of Pd atomic sites at the surfaces. The atomic structures of PdGa surfaces are determined by means of a combined experimental and computational approach allowing investigation of the catalytic dissociation of hydrogen. The two opposite (111) and {{\left( {\bar 1\bar 1\bar 1} \right)}} surfaces show a very different arrangement of catalytic centers.

Aluminium nitride (AlN) bulk single crystals were grown on off-oriented4H-SiC substrates by the sublimation method. High-quality crystals withabout 25 mm in diameter and up to 5 mm in thickness were obtained withan optimized growth process. The crystals show hexagonal symmetry withwell developed 510 (1) over bar16 side facets. Confocal-Ramanspectroscopy and double-crystal X-ray diffraction rocking curve(DCXRD-RC) measurements confirm the high structural quality of the growncrystals. In Raman spectroscopy, the full-width at half maximum (FWHM)of E-2(high) phonon mode decreases from 40 cm(-1) for thin layers (800mu m) to 22 cm(-1) for a 5 mm thick crystal, showing the improvement inquality with thickness. The DCXRD rocking curve FWHM obtained for a 5mmthick crystal is about 120 arcsec. A basal plane bending of 100 arcsecis observed by rocking curve measurements while scanning 17 mm of thesample’s diameter. Two kinds of growth modes namely, step flow growthand spiral growth modes were observed under similar growth conditions.This may be attributed to a slight variation of super-saturation in thegas phase. In both cases, a single active hexagonal growth centre isformed. As-grown surfaces have been found to be always Al-polar. Wetchemical etching revealed both, threading type and basal-planedislocations (BPD) on the surfaces of the samples with total etch pitdensities (EPDs) in the range of 8 x 10(5)-1 x 10(6) cm(-2). (C) 2011WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim

The intermetallic PdGa is a highly selective and potent catalyst in the semihydrogenation of acetylene, which is attributed to the surface stability and isolated Pd atom ensembles. In this context PdGa single crystals of form B with (111) orientation were investigated by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), X-ray photoelectron diffraction (XPD), and low-energy electron diffraction (LEED) to study the electronic and geometric properties of this surface. UPS and thermal desorption spectroscopy (TDS) were used to probe the chemisorption behavior of CO. The PdGa(111) surface exhibits a (1 × 1) LEED and a pronounced XPD pattern indicating an unreconstructed bulk-truncated surface. Low-temperature STM reveals a smooth surface with a (1 × 1) unit cell. No segregation occurs, and no impurities are detected by XPS. The electronic structure and the CO adsorption properties reveal PdGa(111) to be a bulk-truncated intermetallic compound with Pd-Ga partial covalent bonding.

1-inch diameter, (0001)-plane AlN single crystals were grown on 6H-SiC substrates by the sublimation method. With the optimised growth conditions, 1-3 mm thick, yellow-coloured crystals with smooth c -facet and good structural properties were obtained. X-ray diffraction rocking curves show a full width at half maximum (FWHM) value of about 100 arcsec. The crystal surface exhibits 3D-microstructures with different morphologies as observed by laser scanning microscopy. All these structures reflect the hexagonal symmetry. The origin of these structures was further investigated by atomic force microscopy and an overlapping double growth spiral was observed in the middle of these structures that is attributed to a dislocation core. Green colouration observed in some of the grown crystals was analysed with the electron probe microanalysis and the results infer that more incorporation of carbon may be the cause. Further a high silicon content of up to 5.5 wt\% was observed at the top layer of 3 mm thick green-coloured crystals whereas 3 wt\% were measured for the yellow-coloured ones. The distribution of Si is uniform over the entire diameter of the crystals. Yellowish crystals show improved structural properties compared to the greenish ones. The FWHM value and the peak positions of Raman phonon modes represent a high crystalline quality and also confirm that the crystals are relaxed from stress. Raman micro-mapping analysis indicates the presence of small, localized tensile stress on the growth spiral region, whereas this is not observed at smooth areas of the crystal surface without spirals. Uniform E 2(high) FWHM and phonon intensity over the entire mapped area further prove that the grown crystals are structurally very homogeneous.

Complex metallic phases in the Al-Cr-Fe system are considered to beinteresting because of their enhanced resistance against corrosion.Single crystal growth of the Al(4)(Cr,Fe) and Al(13)(Fe,Cr)(4) phases,which is a prerequisite for detailed studies is presented herein for thefirst time. Along with their binary end members Al(4)Cr and Al(13)Fe(4)growth of cm(3)-size crystals was achieved by using the Czochralskimethod from Al-rich solutions at temperatures of approximately 1000degrees C. Special emphasis is put on the refinement of the Al-richcorner of the ternary phase diagram in determining the 1000 degrees Cequilibria between the incongruent melts and the corresponding ternarysolid solutions. Our findings confirm earlier data on the existenceregion of Al(13)(Fe,Cr)(4), but significantly differ from those withrespect to the so called Al(4)(Cr, Fe) phase. It is shown that theexistence region of Al(4)(Cr,Fe) decomposes into four regions ofstructurally different phases depending on the Cr/Fe ratio. Binarymu-Al(4)Cr crystallizes in the hexagonal space group P6(3)/mmc and candissolve only up to about 1 At-\% iron. More Fe-rich alloys crystallizein the orthorhombic space group Cmcm (about 2 At-\% iron) or Immm(containing between 3 and about 6 At-\% iron). For crystals containingabout 7 At-\% iron the structure belongs to the space group R (3) overbar. The grown single crystals were characterized by electron probemicroanalysis revealing only weak segregation effects. The structuralperfection of the orthorhombic phase was studied using X-ray topographywith the Lang technique. Significant anisotropic properties of thisphase allow to discuss structural similarities with decagonalquasicrystals.

Al-based complex metallic alloys (CMAs) are crystalline intermetallic phases characterised by very complex crystal lattices, showing intriguing surface properties such as low wetting, low friction and hardness which include, for the Al–Cr–Fe system, high corrosion resistance. However, their passivation mechanisms (nm-thick oxide layer formation) still need to be understood in relation with localised corrosion susceptibility. New single phases were therefore characterised by electrochemical Microcell technique. The chromium cations in the oxide proved to play a significant role in stabilising the passive layer at low pH. Corrosion resistance of single- and polycrystalline samples was first compared by means of inductively coupled plasma mass spectrometer (ICPMS) analysis during immersion. Higher dissolution rates have been measured for the low Cr containing (12.5 at%) polycrystals compared to the single crystals. The resistance to localised corrosion attack of the single crystals in an aggressive 0.01 M HCl + 1 M NaCl solution at pH 2 was high, with an anisotropic behaviour of the anodic breakdown potential related to the grain orientation. The orthorhombic (0 0 1) termination with higher Cr/Al atoms ratio formed a passive layer with increased resistance against pitting. Ageing of the samples and the formation of surface Al oxy-hydroxide appeared to decrease the pitting corrosion resistance.

The Hall coefficient RH in monoclinic Y-Al-Ni-Co, orthorhombic Al13Co4 and monoclinic Al13Fe4 and Al13(Fe, Ni)4 single crystals has been investigated for all combinations of the electrical current and magnetic field directions and in the temperature interval from 90 to 370 K. In all three intermetallics, which belong to the Al13TM4 (TM = transition metal) class of approximants to the decagonal quasicrystals, the Hall coefficient exhibits well defined anisotropy. RH is positive hole-like or zero for the magnetic field parallel to the plane that corresponds to the quasiperiodic plane in decagonal (d) quasicrystals, and is negative electron-like or zero for the magnetic field perpendicular to this plane. The only exeption is RH in Al13Fe4 for the field parallel to the stacking direction, which changes the sign from positive to negative value with the increase of temperature. The results for the anisotropy of RH are correlated to the anisotropy of RH in d-Al-Ni-Co and d-Al-Cu-Co quasicrystals and a brief overview of the theoretical results is presented.

We compare the growth of a Bi thin film on the ten-fold surface of the decagonal Al-Ni-Co quasicrystal at different substrate temperatures and fluxes using scanning tunneling microscopy (STM) and l...

Single crystal growth of PdGa which is a highly selective catalyst for the semi-hydrogenation of acetylene is reported for the first time. Bridgman as well as Czochralski methods were used starting from off-stoichiometric or congruent melting compositions. While Bridgman growth always resulted in polycrystalline ingots with individual grains restricted to a few millimeters in size, using the Czochralski technique from Ga-rich solutions allowed the growth of PdGa single crystals of several cubic centimeters.