Shape effect on the size and dimension dependent order–disorder transition temperatures of bimetallic alloys

Jiang, Xiaobao; Jiang, Man; Zhao, Ming

doi:10.1016/j.physb.2011.08.093

Cited by 10 publications

(8 citation statements)

References 26 publications

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“…Alam et al proposed that T C is linear with the square of the order parameter; therefore, partial ordering may lead to a decrease of T C . The present variation tendency of T C also agrees with other predictions. − Figure shows the size dependence of the ordering enthalpy and ordering entropy for FePt NPs, while both the ordering enthalpy and ordering entropy decrease with a decrease of the particle size. However, the shape effect is different from the size effect; i.e., the ordering enthalpy increases but the ordering entropy decreases with an increase of the shape factor.…”

Section: Resultssupporting

confidence: 91%

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Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles

Li¹,

Huang³

et al. 2012

J. Phys. Chem. C

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On the basis of our previous work, the Debye model has been generalized for the size- and shape-dependent order–disorder transition and surface order–disorder transition of FePt nanoparticle (NPs) by considering the configuration entropy. The ordering temperature of FePt NPs decreases with a decrease of the particle size for a specific shape and decreases with a decrease of the shape factor at fixed size. The particle size is the dominant factor while the shape is the secondary one in affecting the transition. The ordering process starts from the surface and then propagates to the core, indicating the order–disorder transition is a surface-dominant process. To induce ordering, the annealing temperature should be lower than the surface ordering temperature, which suggests our calculation can be used to determine the highest annealing temperature. The calculation results also suggest that, at a small size and low temperature, the ordered NPs are stable but, at a large size and high temperature, the disordered NPs are stable. The present predictions agree well with the available literature data.

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Section: Resultssupporting

confidence: 91%

“…Miyazaki et al identified the critical size of the ordering of FePt NPs as 1.5–2 nm, below which no ordering occurs. There are also many other studies showing similar results for the order–disorder transition of bimetallic NPs. − …”

Section: Introductionsupporting

confidence: 55%

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles

Li¹,

Huang³

et al. 2012

J. Phys. Chem. C

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“…Concerning the temperature dependence of ordered phases, Jiang et al [17] showed a shape and size effect on the disorder-order temperatures for the Pd3Au1, Pd1Au3 and the Pd1Au1 phases of supported metal particles. Brückner et al [18] addressed the changes in the particle morphology of supported PdAu catalysts for VAM formation at 155°C -190°C in order to explore reasons for catalyst deactivation.…”

mentioning

confidence: 99%

Dynamic Self-Organization of Supported Pd/Au Catalysts during Vinyl Acetate Synthesis

2013

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It is known that vinyl acetate monomer synthesis over bimetallic Pd 1 Au 1 catalysts is highly structurally sensitive and that these structures are dynamically formed and disintegrated in reactant gas atmosphere. Here we show via a combination of bulk and surface sensitive methods that independent of their nominal composition, Pd/Au bimetallic particles undergo marked reconstruction and phase partition during vinyl acetate synthesis. While temperature-induced reorganization of SiO 2 -supported Pd x Au y particles leads to all three thermodynamically metastable phases, i.e., Pd 3 Au, Pd 1 Au 1 , PdAu 3 , with mainly Au-enriched surface compositions, the reactive atmosphere induces selectively the formation of the Pd 1 Au 1 phase and separated Pd particles. The Pd in the Pd 1 Au 1 has higher specific activity and selectivity than the sole Pd nanoparticles, exemplifying the importance of changing its electronic nature. As the Pd 1 Au 1 phase dominates the catalytic activity, novel tailored catalysts could be produced, limiting the presence of dispersed Pd.

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“…Technically the ordering temperature is related to the melting temperature via equation (16), but not all melting models discuss this relationship. Of the two models presented, only model one, reference [49], discusses the ordering transition. In addition to this reference, Li [65] generalized the Bragg-Williams model to include size and shape effects by considering edge and corner atoms, making the model valid for small (∼ 1 nm) dimensions, even though it is not certain that such small particles are ordered.…”

Section: Resultsmentioning

confidence: 99%

“…For monometallic components A (corresponding to x = 1) or B (corresponding to x = 0) and with bond length h from Table 1 we have from Jiang's model [49]:…”

Section: Methodsmentioning

confidence: 99%

Size, shape, and compositional effects on the order–disorder phase transitions in Au–Cu and Pt–M (M = Fe, Co, and Ni) nanocluster alloys

Kaatz

Bultheel

2018

Nanotechnology

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Au-Cu and Pt-M (M = Fe, Co, and Ni) nanocluster alloys are currently being investigated world-wide by many researchers for their interesting catalytic and nanophase properties. The low temperature behavior of the phase diagrams is not well understood for alloys with nanometer sizes and shapes. We consider two models for low temperature ordering in the phase diagrams of Au-Cu and Pt-M nanocluster alloys. These models are valid for sizes ∼5 nm and approach bulk values for sizes ∼20 nm. We study the phase transitions in nanoclusters with cubic, octahedral, and cuboctahedral shapes, covering the compositions of interest. These models are based on studying the melting temperatures in nanoclusters using the regular solution, mixing model for alloys. From our data, experiments on nanocubes about 5 nm in size, of stoichiometric AuCu and PtM composition, could help differentiate between the models. Dispersion data shows that for the three shapes considered, octahedra have the highest percentage of surface atoms for the same relative diameter. We summarize the effects of structural ordering on the catalytic activity and suggest a method to avoid sintering during annealing of Pt-M alloys.

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Shape effect on the size and dimension dependent order–disorder transition temperatures of bimetallic alloys

Cited by 10 publications

References 26 publications

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles

Dynamic Self-Organization of Supported Pd/Au Catalysts during Vinyl Acetate Synthesis

Size, shape, and compositional effects on the order–disorder phase transitions in Au–Cu and Pt–M (M = Fe, Co, and Ni) nanocluster alloys

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Shape effect on the size and dimension dependent order–disorder transition temperatures of bimetallic alloys

Cited by 10 publications

References 26 publications

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe0.5Pt0.5 Nanoparticles

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe0.5Pt0.5 Nanoparticles

Dynamic Self-Organization of Supported Pd/Au Catalysts during Vinyl Acetate Synthesis

Size, shape, and compositional effects on the order–disorder phase transitions in Au–Cu and Pt–M (M = Fe, Co, and Ni) nanocluster alloys

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Product

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Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles

Modeling the Size- and Shape-Dependent Surface Order–Disorder Transition of Fe_0.5Pt_0.5 Nanoparticles