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[Display omitted] • A straightforward first-principles based method is proposed to determine the average electron band structure of disordered solids using supercell approach. • The average band gap and average effective mass of electron/hole in different valleys have been calculated for a number of alloys. • The method has the potential to explain and predict the experimental observations. • The method can be used to investigate the role of order/disorder in electronic properties of imperfect solids in one, two and three dimensions. In this paper, a straightforward first-principles based method is proposed to determine the average effective electron band structure of disordered solids using supercell approach and plane-wave basis. Calculations have been done by determining the expectation values of the supercell Hamiltonian in a primitive-cell-periodic basis. The formulation and implementation details are presented and discussed. Also, it is shown that, in the cases with small differences in bonding characteristics at atomic-scale resolution, the weighted average bands are almost continuous. Therefore, it is possible to calculate the average effective band gap and average effective mass of electron/hole in different valleys. Analysis of the results for a number of disordered compounds shows that the proposed technique has the potential to explain and predict the experimental observations. This method is a promising tool for the study of the role of order/disorder in the electronic properties of random alloys and 2D and 3D imperfect materials. [ABSTRACT FROM AUTHOR]

Thanks to a dedicated modelling of intensities, the depth sensitivity of X-ray photoemission is used to probe the segregation profile of aluminium at the (110), (100) and (111) low index surfaces of the body-centred Fe 0.85 Al 0.15 random alloy. Sputtered surface composition is close to the nominal bulk one, thus excluding preferential sputtering. Surface enrichment in aluminium upon annealing starts at around 700 K before reaching a stationary state above 1000 K. The average surface composition is close to Fe 0.5 Al 0.5 , corresponding to the B 2 CsCl structure of the phase diagram. The impacted depth, that is in the range of 2.5–3.5 nm, is quite significant. Although not evidenced previously in surface science conditions at FeAl single crystal surfaces, it is qualitatively in agreement with the segregation at grain boundaries and shear planes of Al-alloyed steels. This segregation tendency is rationalized through ab initio calculations. Unlabelled Image • Severe aluminium segregation above 700 K at the surfaces of bcc Fe 0.85 Al 0.15 • Photoemission determination of the concentration profile in a random alloy • Nanometer deep impacted layer with a Fe 0.5 Al 0.5 composition • Ab initio modelling of segregation trends [ABSTRACT FROM AUTHOR]

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (1 1 0) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900  K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5  nm that run along the [ 0 0 1 ] B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements. [ABSTRACT FROM AUTHOR]

Bimetallic nanoparticle catalysts of PtRh supported on carbon were synthesized using an electron beam irradiation reduction method. The PtRh nanoparticle catalysts were composed of particles 2–3 nm in size, which were well dispersed on the surface of the carbon support nanoparticles. Analyses of X-ray diffraction and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy revealed that the PtRh nanoparticles have a randomly alloyed structure. The lattice constant of the PtRh nanoparticles showed good correlation with Vegard's law. These results are explained by the radiochemical formation process of the PtRh nanoparticles. Catalytic activities of PtRh/C nanoparticles for ethanol oxidation reaction were found to be higher than those obtained with Pt/C. [ABSTRACT FROM AUTHOR]

Abstract: When a mixture of H2PdCl4 and AgNO3 was co-reduced by ascorbic acid in aqueous solution in the presence of CTAB as a surfactant, aside from irregular shapes of Pd–Ag alloy particles, new cubic Pd–Ag alloy nanocrystals were prepared. The transmission electron microscopic (TEM)–energy dispersed X-ray spectroscopic (EDS) data at the atomic level suggest that Pd–Ag cubic alloys surrounded by {100} facets consist of substitutional solid solution and the arrangement of the solute Ag atoms is random. The Ag atomic content in Pd–Ag alloy must be less than ≈22% for preservation of the cubic structure. Optical properties of Pd–Ag alloys were characterized by observing the extinction spectra in the ultraviolet(UV)–visible(vis) range. [Copyright &y& Elsevier]

Abstract: Au–Pd bimetallic nanoparticles supported on carbon particles were synthesized by reduction of precursor ions in an aqueous solution irradiated with a high energy electron beam. The composition of the samples was analyzed by the inductively coupled plasma atomic emission spectrometry (ICP-AES), and the morphology of the samples was observed by the transmission electron microscope (TEM). TEM micrographs indicated that Au–Pd particles of ca. 5-nm were well dispersed on the surface of carbon particles of ca. 30-nm without any serious agglomeration. Addition of citric acid to the initial solution and high pH were found to be effective for formation of random alloy structure in the resultant bimetallic nanoparticles. The change in the bimetallic structure from core–shell to random alloy was identified by techniques of the X-ray diffraction (XRD) and the extended X-ray absorption fine structure (EXAFS). [Copyright &y& Elsevier]

• The (100) surface is the most stable surface for the random Al x Ti 1 - x N alloys. • Ti segregation to the surface is enhanced at high Al concentrations. • This helps explain the formation of a lamella structure in industrial coatings. • N vacancy segregation to the surface is similarly enhanced at high Al concentrations. The (100), (110) and (111) surface energies of random Al x Ti 1 - x N alloys with homogeneous concentration profile are determined in first-principles calculations. The (100) surface has the lowest energy of 1.25 J/m2 in the case of TiN and 1.32 J/m2 for cubic AlN and exhibit very little concentration dependence. The (110) and (111) surfaces have much higher energy for all the compositions. The segregation energies of Ti and Al were obtained for the (100) surface of pure TiN and cubic AlN as well as Al 0.5 Ti 0.5 N and Al 0.9 Ti 0.1 N random alloys. In the latter case, we have used two different methods: direct averaging of the substitution energies with respect to the local environment of the substitution site and the cluster expansion technique (CLE). We find that the segregation of Ti is favorable in the whole concentration range of random Al x Ti 1 - x N alloys. However, it is weak in almost the whole concentration range except in the Al-rich alloys: Al 0.9 Ti 0.1 N and cubic AlN. The strengthening of the surface segregation of Ti in the latter case is related to the sharp increase in phase separation tendency in Al x Ti 1 - x N alloys at compositions close to pure AlN. The increased tendency for Ti segregation close to pure AlN helps explain the formation of a lamella structure in industrially important Al x Ti 1 - x N coatings. As for nitrogen vacancies, their segregation energies are relatively small in the whole concentration range, but for pure AlN where they exhibit strong preference for the surface. The latter is obviously connected with the fact that cubic AlN has a high degree of ionic bonding and a vacancy creation on the nitrogen sublattice is highly energetically unfavorable, especially in the bulk due to a larger number of Al-N ionic bonds. [ABSTRACT FROM AUTHOR]

Magnetic properties of the (0 0 1) surface of pure vanadium and disordered binary Mo–V alloys have been investigated from the first-principles by means of the LMTO-GF-CPA technique, the fixed spin moment method, and the direct exchange Monte-Carlo statistical mechanics simulations. The binary alloys, as well as pure constituent metals, are nonmagnetic in the bulk. However, we have shown that the (1 0 0) surface of uniformly random and segregated Mo–V alloys is magnetic. The magnetism of the V monolayer on the Mo(0 0 1) surface has also been studied. In particular, the surface relaxation effect has resulted in a reduction of the magnetic moments for V atoms, but the surface magnetism is still present in the system. Including of semi-core states as valence ones does not alter this conclusion. [Copyright &y& Elsevier]