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Oxidation of the two-phase Nb/Nb5Si3 composite: The role of energetics, thermodynamics, segregation, and interfaces
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10.1063/1.4773447
/content/aip/journal/jcp/138/1/10.1063/1.4773447
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/1/10.1063/1.4773447
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Figures

Image of FIG. 1.
FIG. 1.

The structure models of bulk Nb5Si3 (a) and the Nb5Si3(001) surface with terminations of NbSi, Nb, Si, and Nb, which are denoted as Nb5Si3(001)-NbSi (b), Nb5Si3(001)-Nb1 (c), Nb5Si3(001)-Si (d), and Nb5Si3(001)-Nb2 (e), respectively.

Image of FIG. 2.
FIG. 2.

The structure models of the Nb(001)/Nb5Si3(001) interface: (a) Nb(001)/Nb5Si3(001)-NbSi, (b) Nb(001)/Nb5Si3(001)-Nb1, (c) Nb(001)/Nb5Si3(001)-Si, and (d) Nb(001)/Nb5Si3(001)-Nb2.

Image of FIG. 3.
FIG. 3.

Surface energies of Nb(110), Nb5Si3(110), Nb5Si3(111), and Nb5Si3(001) with different terminations as functions of the chemical potential of Nb. Nb5Si3(001)-NbSi, Nb5Si3(001)-Nb1, Nb5Si3(001)-Si, and Nb5Si3(001)-Nb2 denote the Nb5Si3(001) surface with terminations of NbSi, Nb, Si, and Nb, respectively. The vertical line indicates the position of the crossing point.

Image of FIG. 4.
FIG. 4.

Binding energies of oxygen on the clean Nb(110) and Nb5Si3(001)-Si surfaces at the most stable adsorption site as functions of the oxygen coverage in a range of 0 < Θ ≤ 1.

Image of FIG. 5.
FIG. 5.

Three-dimensional surface phase diagram for the oxygen-adsorbed two-phase composite system, O-Nb/Nb5Si3, as functions of μ Nb and μ O, respectively. The 3D SPD contains the surface energies of the most stable O-Nb(110) and O-Nb5Si3(001) systems. 2O, 3O, and 4O represent adsorption of two, three, and four oxygen atoms on the Nb(110) or Nb5Si3(001) surface, corresponding to the oxygen coverage of 0.50, 0.75, and 1.0 ML, respectively. The surface energies of the O-Nb(110) surfaces are always lower than that of O-Nb5Si3(001) surfaces under O-rich conditions.

Image of FIG. 6.
FIG. 6.

Surface energies of the most stable oxygen-covered Nb(110) and Nb5Si3(001) surfaces as functions of μ O under (a) extreme Nb-poor condition and (b) extreme Nb-rich condition. (c) Two-dimensional surface phase diagram for the O/Nb5Si3(001) system in terms of μ Nb and μ O. The extreme Nb-poor and extreme Nb-rich conditions correspond to the minimum and maximum values of μ Nb in (c), respectively. 1O, 2O, 3O, and 4O represent the adsorption of one, two, three, and four oxygen atoms on the Nb(110) or Nb5Si3(001) surface, respectively.

Image of FIG. 7.
FIG. 7.

(a) Oxygen binding energies (per oxygen atom) in bulk Nb and bulk Nb5Si3 at the most stable binding sites as functions of oxygen concentration. (b) Average oxygen binding energies at the most stable adsorption sites of the Nb(110) surface forming the surface oxide as a function of oxygen coverage for the oxygen coverage of 1 < Θ 2. The average binding energies of oxygen adsorption on Nb(110) at 1.00 ML and 2.00 ML are also plotted in (a) for comparison.

Image of FIG. 8.
FIG. 8.

(a) Interface formation energies of Nb(001)/Nb5Si3(001) with different interface terminations as functions of the chemical potential of Nb. Upon optimization, Nb/Nb5Si3(001)-Nb1 and Nb/Nb5Si3(001)-NbSi have the same structure, and Nb/Nb5Si3(001)-Nb2 and Nb/Nb5Si3(001)-Si share the same interfacial structure. (b) Oxygen binding energies (per oxygen atom) in the Nb(001)/Nb5Si3(001)-Nb1 and -Nb2 interface systems at the most stable local sites as functions of the distance between the oxygen atom and the interface. The vertical dashed line in (b) denotes the corresponding interface position of the Nb1 and Nb2 layers.

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/content/aip/journal/jcp/138/1/10.1063/1.4773447
2013-01-07
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Oxidation of the two-phase Nb/Nb5Si3 composite: The role of energetics, thermodynamics, segregation, and interfaces
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/1/10.1063/1.4773447
10.1063/1.4773447
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