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Size-dependent phase diagrams of metallic alloys: A Monte Carlo simulation study on order-disorder transitions in Pt-Rh nanoparticles

Pohl, Johan and Stahl, Christian and Albe, Karsten (2012):
Size-dependent phase diagrams of metallic alloys: A Monte Carlo simulation study on order-disorder transitions in Pt-Rh nanoparticles.
In: Beilstein Journal of Nanotechnology, Beilstein Institut, pp. 1-11, 3, [Online-Edition: http://www.beilstein-journals.org/bjnano/single/articleFullT...],
[Article]

Abstract

Nanoparticles of Pt–Rh were studied by means of lattice-based Monte Carlo simulations with respect to the stability of ordered D022- and 40-phases as a function of particle size and composition. By thermodynamic integration in the semi-grand canonical ensemble, phase diagrams for particles with a diameter of 7.8 nm, 4.3 nm and 3.1 nm were obtained. Size-dependent trends such as the lowering of the critical ordering temperature, the broadening of the compositional stability range of the ordered phases, and the narrowing of the two-phase regions were observed and discussed in the context of complete size-dependent nanoparticle phase diagrams. In addition, an ordered surface phase emerges at low temperatures and low platinum concentration. A decrease of platinum surface segregation with increasing global platinum concentration was observed, when a second, ordered phase is formed inside the core of the particle. The order–disorder transitions were analyzed in terms of the Warren–Cowley short-range order parameters. Concentration-averaged short-range order parameters were used to remove the surface segregation bias of the conventional short-range order parameters. Using this procedure, it was shown that the short-range order in the particles at high temperatures is bulk-like.

Item Type: Article
Erschienen: 2012
Creators: Pohl, Johan and Stahl, Christian and Albe, Karsten
Title: Size-dependent phase diagrams of metallic alloys: A Monte Carlo simulation study on order-disorder transitions in Pt-Rh nanoparticles
Language: English
Abstract:

Nanoparticles of Pt–Rh were studied by means of lattice-based Monte Carlo simulations with respect to the stability of ordered D022- and 40-phases as a function of particle size and composition. By thermodynamic integration in the semi-grand canonical ensemble, phase diagrams for particles with a diameter of 7.8 nm, 4.3 nm and 3.1 nm were obtained. Size-dependent trends such as the lowering of the critical ordering temperature, the broadening of the compositional stability range of the ordered phases, and the narrowing of the two-phase regions were observed and discussed in the context of complete size-dependent nanoparticle phase diagrams. In addition, an ordered surface phase emerges at low temperatures and low platinum concentration. A decrease of platinum surface segregation with increasing global platinum concentration was observed, when a second, ordered phase is formed inside the core of the particle. The order–disorder transitions were analyzed in terms of the Warren–Cowley short-range order parameters. Concentration-averaged short-range order parameters were used to remove the surface segregation bias of the conventional short-range order parameters. Using this procedure, it was shown that the short-range order in the particles at high temperatures is bulk-like.

Journal or Publication Title: Beilstein Journal of Nanotechnology
Volume: 3
Publisher: Beilstein Institut
Uncontrolled Keywords: Monte Carlo simulation; nanoparticles; nanothermodynamics; phase diagram; Pt-Rh; thermodynamics
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 21 Mar 2012 09:40
Official URL: http://www.beilstein-journals.org/bjnano/single/articleFullT...
Identification Number: doi:10.3762/bjnano.3.1
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