Monotonous concentration profile and reconstruction at Pt80Fe20(111): LEED study of a catalyst

Beccat, P.; Gauthier, Yves; Baudoing-Savois, R.; Bertolni, J.C.

doi:10.1016/0039-6028(90)90069-k

Cited by 75 publications

(41 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…4, I show the similar off-stoichiometric effect at the ͑111͒ surface of ordered Pt 3 Fe. Here, the surface of the Pt-rich alloy is completely covered by Pt while the surface composition of the Fe-rich alloy should be stoichiometric, at least at temperatures well below the order-disorder transition temperature of 1400 K. These results are partially confirmed by several experimental investigations 14,15 which have established that the ͑111͒ surface of ordered Pt 80 Fe 20 is almost entirely covered by Pt atoms. Unfortunately, no other compositions of this ordered alloy have been investigated.…”

supporting

confidence: 74%

Surface composition of ordered alloys: An off-stoichiometric effect

Ruban

2002

Phys. Rev. B

View full text Add to dashboard Cite

supporting

confidence: 74%

Surface composition of ordered alloys: An off-stoichiometric effect

Ruban

2002

Phys. Rev. B

View full text Add to dashboard Cite

“…All potentials in this paper are, however, referenced to the reversible hydrogen electrode potential (RHE) at the same temperature (calibrated from hydrogen oxidation reaction [13]) in the same electrolyte; argon, oxygen and hydrogen were bubbled through a glass frit (Air Products, 5N8 purity [18] and Pt x Rh 1-x (hkl) [19;20] alloys all exhibit compositional oscillations of alloying components in the first three atomic layers. For most (111) and (100) crystals, the outermost layer of the clean, annealed surfaces are pure Pt, which we shall call hereafter the "skin" structure, with Pt depletion in the second layer.…”

Section: Electrochemical Measurementsmentioning

confidence: 99%

Surface segregation effects in electrocatalysis: kinetics of oxygen reduction reaction on polycrystalline Pt 3 Ni alloy surfaces

Stamenković

Schmidt

Ross

et al. 2003

Journal of Electroanalytical Chemistry

345

292

View full text Add to dashboard Cite

Effects of surface segregation on the oxygen reduction reaction (ORR) have been studied on a polycrystalline Pt 3 Ni alloy in acid electrolyte using ultra high vacuum (UHV) surface sensitive probes and the rotating ring disk electrode (RRDE) method. Preparation, modification and characterization of alloy surfaces were done in ultra high vacuum (UHV). Depending on the preparation method, two different surface compositions of the Pt 3 Ni alloy are produced: a sputtered surface with 75 % Pt and an annealed surface (950 K ) with 100 % Pt. The latter surface is designated as the "Pt-skin" structure, and is a consequence of surface segregation, i.e., replacement of Ni with Pt atoms in the first few atomic layers. Definitive surface compositions were established by low energy ion scattering spectroscopy (LEISS). The cyclic voltammetry of the "Pt-skin" surface as well as the pseudcapacitance in the hydrogen adsorption/desorption potential region is similar to a polycrystalline Pt electrode. Activities of ORR on Pt 3 Ni alloy surfaces were compared to polycrystalline Pt in 0.1M HClO 4 electrolyte for the observed temperature range of 293 < T < 333 K. The order of activities at 333 K was: "Pt-skin" > Pt 3 Ni (75% Pt) > Pt with the maximum catalytic enhancement obtained for the "Pt-skin" being 4 times 1 that for pure Pt. Catalytic improvement of the ORR on Pt 3 Ni and "Pt-skin" surfaces was assigned to the inhibition of Pt-OH ad formation (on Pt sites) versus polycrystalline Pt. Production of H 2 O 2 on both surfaces were similar compared to the pure Pt. Kinetic analyses of RRDE data confirmed that kinetic parameters for the ORR on the Pt 3 Ni and "Pt-skin" surfaces are the same as on pure Pt: reaction order, m=1, two identical Tafel slopes, activation energy, ≈ 21-25 kJ/mol. Therefore the reaction mechanism on both Pt 3 Ni and "Pt-skin" surfaces is the same as one proposed for pure Pt i.e. 4e -reduction pathway.

show abstract

“…The fact agrees with the Pt segregation tendency previously observed and calculated in FePt. [9][10][11][12][13][35][36][37][38][39] The data show that We perform a comparison between the most-outer-layer surface segregation energies of Ag, Au, and Cu in L1 0 -FePt and those in pure Fe or Pt as previously calculated with the Korringa-Kohn-Rostoker atomic sphere and local density approximation ͑KKR-ASA-LDA͒ method. 40,41 For this task, we restrict Eq.…”

mentioning

confidence: 94%

First principles study of Ag, Au, and Cu surface segregation in FePt-L1

Chepulskii

Curtarolo

2010

Applied Physics Letters

View full text Add to dashboard Cite

Doping FePt nanoparticles could be a possible approach to achieve high L1 0 order and magnetic anisotropy. To address stability, first-principles studies of surface segregation of dilute Ag/Au/Cu solutes at and near the ͑001͒/͑100͒/͑111͒ surfaces of FePt-L1 0 are performed. It is found that a strong surface segregation tendency at first outer layer is present in all the cases. For Cu, segregation is less than half of Ag and Au. Ag and Cu segregate to Fe sites at surfaces and preferentially substitute for Fe in the bulk, whereas Au substitutes for Fe at surfaces and for Fe and Pt in the bulk. © 2010 American Institute of Physics. ͓doi:10.1063/1.3522652͔In the past decade, FePt nanoparticles have been extensively investigated in view of possible future applications as an ultrahigh-density information-storage medium and highperformance permanent magnets. [1][2][3][4][5][6] The critical issue for information-storage application is the presence of magnetic anisotropy offering sufficiently large thermal stability. In FePt, a high magnetic anisotropy is guaranteed by an ordered L1 0 phase. However, experimental observations 4-6 have shown a difficulty in obtaining a high degree of L1 0 order in FePt nanoparticles annealed at T Շ 600°C with diameter less than ϳ4 nm. The phenomenon has been explained with size, kinetic, and surface segregation effects. [7][8][9][10][11][12][13] One of the possible approaches to achieve high L1 0 order and a correspondingly high magnetic anisotropy is by doping FePt nanoparticles with a third element. 1,3 Atomic species such as Ag, [14][15][16][17][18][19][20] Au,17,[19][20][21][22][23][24][25] and Cu 25-27 have been previously tested. To follow this approach, it is imperative to determine whether dopants concentrate inside the particle cores or segregate at the surfaces. In the latter case, the additional surface vacancies generated by the atoms rearranging on the surface during segregation upon annealing might increase Fe and Pt mobilities and help the particles to reach their L1 0 equilibrium. 16,21,27 Moreover, modeling and explaining surface segregation phenomena are important to understand catalysis, oxidation, and corrosion in nanostructured systems with high surface to volume ratio.In this letter, we study the segregation of dilute Ag, Au, and Cu solutes on and near the ͑001͒, ͑100͒, and ͑111͒ surfaces of FePt crystals with perfect L1 0 order ͑directions are defined with respect to Ref. 9͒. The results can also be used to draw conclusions regarding surface segregation in FePt nanocrystals with ͑001͒ and ͑111͒ facets such as cubes, tetrahedrons, octahedrons, cubeoctahedrons, truncated cubes, and the truncated octahedrons experimentally observed. [28][29][30] We consider ͑001͒, ͑100͒, and ͑111͒ slabs with perfect L1 0 order. For the ͑100͒ and ͑111͒ cases we choose the systems to have eight layers, while for the ͑001͒ slabs we consider nine layers ͑see Fig. 1 of Ref. 9͒. The vacuum thickness between the periodic replica of the slabs is fixed at ϳ12 Å. One substitutional impurity of ...

show abstract

Monotonous concentration profile and reconstruction at Pt80Fe20(111): LEED study of a catalyst

Cited by 75 publications

References 12 publications

Surface composition of ordered alloys: An off-stoichiometric effect

Surface composition of ordered alloys: An off-stoichiometric effect

Surface segregation effects in electrocatalysis: kinetics of oxygen reduction reaction on polycrystalline Pt 3 Ni alloy surfaces

First principles study of Ag, Au, and Cu surface segregation in FePt-L1

Contact Info

Product

Resources

About