Segregation at alloy surfaces
TL;DR: In this paper, a theory for segregation at alloy surfaces, where both the bond breaking and strain theories have been combined into one, is presented, and good agreement is obtained with Auger electron spectroscopy data on a Ni-Au system.
Abstract: We present a theory for segregation at alloy surfaces, where both the bond breaking and strain theories have been combined into one. The formulation can be applied to alloys of any concentration. In addition to it we present some ideas which should be considered while dealing with polycrystalline samples. Good agreement is obtained with Auger electron spectroscopy data on a Ni-Au system.
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TL;DR: In this article, the authors applied AES and LEED to the study of silicon surface segregation on Fe−3wt%Si single crystals between 400 and 900°C, and showed that the repelling of Si by C on the surface is mainly due to a site competition reaction, whereby the strong Si-C repulsive interaction plays a minor role.
Abstract: AES and LEED are applied to the study of silicon surface segregation on Fe−3wt%Si single crystals between 400 and 900°C. The variations of the Si coverage with time at a given temperature or with the temperature at equilibrium show a strong orientation dependence. For the (100) orientation, the diffusivity and segregation enthalpy of silicon on iron could be derived from the measurements. Lateral interactions between segregated atoms are better observed in the presence of a third element. The study of the Fe-Si-C ternary system thus confirmed the weakness of the Si-Si lateral interactions. It also showed that the repelling of Si by C on the surface is mainly due to a site competition reaction, whereby the strong Si-C repulsive interaction plays a minor role.
75 citations
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TL;DR: In this paper, the generalized surface free enthalpy is defined for any (equilibrium or nonequilibrium) segregation profile and its γ ∗ minimal value is connected with the segregation profile of the stable equilibrium state.
Abstract: First, it is argued that the surface free enthalpy and not the surface free energy is the important quantity. The generalized surface free enthalpy γ is defined for any (equilibrium or nonequilibrium) segregation profile and its γ ∗ minimal value is connected with the segregation profile of the stable equilibrium state. Then a calculational method is shown by which the surface free enthalpies of all solid chemical elements may be calculated for any temperature. Then the approximate calculation of other factors of surface segregation is outlined for binary alloys. Examples, in good agreement with the experimental information, are shown for a number of binary monophasic solid and liquid alloys. The problem of monotonie and alternating segregation profiles is also discussed.
66 citations
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TL;DR: This comprehensive review presents results of many such developments in this fast-growing field including endohedrally doped Al, Ga, and In clusters, and performs ab initio calculations to present updated results of the most stable atomic structures and fundamental electronic properties of the endohedral doped cage clusters.
Abstract: The discovery of carbon fullerene cages and their solids opened a new avenue to build materials from stable cage clusters as “artificial atoms” or “superatoms” instead of atoms. However, cage clust...
54 citations
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TL;DR: In this paper, the ground states of neutral and anionic ionic clusters were analyzed and it was shown that both neutral and charged ionic cluster prefer icosahedral structure, in agreement with previous calculations.
Abstract: First-principles calculations have been performed to study the ground states of both neutral and anionic ${\mathrm{Al}}_{12}X$ ($X=\mathrm{Si}$, Ge, Sn, Pb) clusters. We find that both neutral and charged ${\mathrm{Al}}_{12}\mathrm{Si}$ cluster prefer icosahedral structure, in agreement with previous calculations. However, each of ${\mathrm{Al}}_{12}X$ ($X=\mathrm{Ge}$, Sn, Pb), either neutral or anionic clusters, shows symmetry of ${\mathrm{C}}_{5v}$ with atom $X$ located on the cluster surface, contrary to the conclusion from the previous experimental work [Phys. Rev. B 65, 153404 (2002)].
46 citations
References
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01 Jan 1973
TL;DR: A complete revision of the work, Selected Values of Thermodynamic Properties of Metals and Alloys, by Hultgren, Orr, Anderson, and Kelley, published in 1963 by John Wiley and Sons, New York, is presented in this paper.
Abstract: : This volume, together with its companion, Selected Values of Thermodynamic Properties of the Elements, represents a complete revision of the work, Selected Values of Thermodynamic Properties of Metals and Alloys, by Hultgren, Orr, Anderson, and Kelley, published in 1963 by John Wiley and Sons, New York. The work should cover pertinent data available at the date printed on the first page of each system. Inspection will show that many or most of the selected values differ from the 1963 edition; many of the differences are substantial. This shows progress in measurement and, at the same time, hints of uncertainties still present.
2,732 citations
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TL;DR: In this article, the Electronic Structure of Primary Solid Solution in Metals (ESSPSS) in metals is discussed. But the structure of primary solid solutions is not discussed.
Abstract: (1954). Electronic structure of primary solid solutions in metals. Advances in Physics: Vol. 3, No. 12, pp. 446-507.
909 citations
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TL;DR: In this paper, the surface composition of binary alloys is determined by minimizing alloy surface free energy with respect to atom exchange between the surface and the bulk, using a pairwise bound model of the solid with a broken bond surface.
Abstract: The surface composition of binary alloys is determined by minimizing alloy surface free energy with respect to atom exchange between the surface and the bulk. The theory is developed using a pairwise bound model of the solid with a broken bond surface. Parametric predictions for the atom fraction in the first four atomic layers for ideal and regular alloy solutions are presented. The predictions are based on pure element vaporization enthalpies and alloy solution activity coefficients. The surface atom fraction is different from the bulk atom fraction for all bulk compositions. The alloy element with the lower heat of vaporization is enriched with respect to its bulk atom fraction. The effects of chemisorption of a foreign species and alloy particle size on surface composition are also quantified. The theory is in good agreement with existing data on nickel-copper surface compositions.
540 citations
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TL;DR: In this paper, a unified formalism of surface segregation was proposed for grain boundary segregation based on the reduction in lattice strain energy which accompanies the transfer of misfitting solute atoms from the lattice to the boundary.
Abstract: Previous models of surface segregation have generally been based on the assumption that a decrease in surface free energy constitutes the predominant driving force for the phenomenon. In contrast, grain boundary segregation models have been founded on the postulate that the major driving force for that phenomenon is the reduction in lattice strain energy which accompanies the transfer of misfitting solute atoms from the lattice to the boundary. These two concepts have been combined here into a single unified formalism of surface segregation. In addition, the temperature dependence of surface composition of both nickel-rich and gold-rich nickelgold alloys has been measured by Auger electron spectroscopy. Comparisons of the predictions of the combined formalism with the experimental results show excellent agreement between measured and calculated heats of adsorption (segregation). Furthermore, the present formalism provides estimates of the entropies of adsorption which can be used to explain apparent incompatibilities between the behavior of gold-rich and nickel-rich alloys.
351 citations