3D phase diagrams and the thermal stability of two-component Janus nanoparticles: effects of size, average composition and temperature

Taranovskyy, Andriy; Tomán, János J.; Gajdics, Bence; Erdélyi, Zoltán

doi:10.1039/d0cp06695h

Cited by 6 publications

(8 citation statements)

References 52 publications

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“…It was shown that the equilibrium compositions of the phases in Janus nanoparticles change with both the particle’s size and average composition. This means that the use of 3D phase diagrams is required bimetallic nanoparticles . Furthermore, the shape of the phase diagram depended on the interface structure of the two-phase nanoparticle.…”

Section: Introductionmentioning

confidence: 99%

Effect of Size on the Formation of Solid Solutions in Ag–Cu Nanoparticles

2023

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Modern technologies stimulate the quest for multicomponent nanosized materials with improved properties, which are ultimately defined by the atomic arrangement and interphase interactions in the nanomaterial. Here, we present the results of the experimental study of the formation of solid solutions in Ag−Cu nanoparticles in a wide size and temperature range using in situ TEM techniques. The Ag−Cu nanoparticles with a eutectic ratio of components were formed on an amorphous carbon film by the physical vapor deposition technique. Electron diffraction, HAADF-STEM imaging, energy-dispersive X-ray spectroscopy, chemical element mapping, and electron energy loss spectral imaging were used for the characterization of mixing patterns and composition of phases in AgCu nanoparticles down to the atomic level. As a result, we constructed the solid-state part of the Ag−Cu phase diagram for nanoparticles with a size down to 5 nm. We found a highly asymmetric behavior of the solvus lines. Thus, the content of Cu in Ag gradually increased with a size reduction and reached the ultimate value for our configuration of 27 wt % Cu at a nanoparticle size below ∼8 nm. At the same time, no Cu-rich solid solution was found in two-phase AgCu nanoparticles, irrespective of the size and temperature. Moreover, a quasi-homogeneous solid solution was revealed in AgCu nanoparticles with a size smaller than 8 nm already at room temperature. A size dependence of the terminal temperature T term , which limits the existence of AgCu alloy nanoparticles in a vacuum, was constructed. Evaporation of the AgCu phase with the composition of 86 wt % Ag was observed at temperatures above T term . We show the crucial role of the mutual solubility of components on the type of atomic mixing pattern in AgCu nanoparticles. A gradual transition from a Janus-like to a homogeneous mixing pattern was observed in Ag−Cu nanoparticles (28 wt % Cu) with a decrease in their size.

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Section: Introductionmentioning

confidence: 99%

Effect of Size on the Formation of Solid Solutions in Ag–Cu Nanoparticles

2023

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“…We should note that the lever rule is not applicable to nanophase separation diagrams, similarly to a case of melting transitions. , The rule, related to conservation of the elemental atom numbers in the NP, does work for the complementary and less familiar “solubility diagrams”, presenting the equilibrium compositions of the two separated nanophases. , (For macrosystems the two types of diagrams coincide.) In the present case of the Pd–Ir core, average compositions vs temperature have been chosen and obtained by using the site concentrations of the Pd-rich and Ir-rich nanophases (e.g., shown above in Figure a; this choice differs from the solubility definition using maximal and minimal site concentrations). Compared to the bulk alloy, the computed solubility diagrams (Figure a) reveal enhanced miscibility (also observed for Au–Rh), which increases with the NP size decrease.…”

Section: Resultsmentioning

confidence: 99%

“…33,13 (For macrosystems the two types of diagrams coincide.) In the present case of the Pd−Ir core, average compositions vs temperature have been chosen and obtained by using the site concentrations of the Pd-rich and Ir-rich nanophases (e.g., shown above in Figure 6a; this choice differs from the solubility definition using maximal and minimal site concentrations 33 ). Compared to the bulk alloy, the computed solubility diagrams (Figure 10a) reveal enhanced miscibility (also observed for Au−Rh 2 ), which increases with the NP size decrease.…”

Section: Resultsmentioning

confidence: 99%

“…41,48 The rule, related to conservation of the elemental atom numbers in the NP, does work for the complementary and less familiar "solubility diagrams", presenting the equilibrium compositions of the two separated nanophases. 33,13 (For macrosystems the two types of diagrams coincide.) In the present case of the Pd−Ir core, average compositions vs temperature have been chosen and obtained by using the site concentrations of the Pd-rich and Ir-rich nanophases (e.g., shown above in Figure 6a; this choice differs from the solubility definition using maximal and minimal site concentrations 33 ).…”

Section: Resultsmentioning

confidence: 99%

“…Vibrational entropy contributions to the thermal stability of the separated nanophases were usually ignored in those and other studies. , The present study demonstrates that a destabilizing effect can be quite significant, in agreement with general conclusions made earlier regarding bulk alloys . Furthermore, solubility diagrams are typically absent in the NP literature, and predictions of the size dependence of the transition temperature T nano , namely, phase diagrams for several nanosizes, are quite rare. In those studies involving several NP sizes, a possible finite-size scaling law of the critical temperature T C nano was not inspected (except for the case of fcc rectangular nanoparticles studied by us recently).…”

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confidence: 99%

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The Thermal Stability of Asymmetric Separated Configurations inside Alloy Nanoparticles: Atomic-Scale Modeling of Pd–Ir Nanophase Diagrams

Polak

Rubinovich

2022

ACS Nano

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Compared to alloy bulk phase diagrams, the experimental determination of phase diagrams for alloy nanoparticles (NPs), which are useful in various nanotechnological applications, involves significant technical difficulties, making theoretical modeling a feasible alternative. Yet, being quite challenging, modeling of separation nanophase diagrams is scarce in the literature. The task of predicting comprehensive nanophase diagrams for Pd−Ir face-centered cubic-based three cuboctahedra is facilitated in this study by combining the computationally efficient statistical-mechanical Free-energy Concentration Expansion Method, which includes short-range order (SRO) with coordination-dependent bond-energy variations as part of the input and with rotationally symmetric site grouping for extra efficiency. This nanosystem has been chosen mainly because of the very small atomic mismatch that simplifies the modeling, e.g., in the assessment of vibrational entropy contributions based in this work on fitting to the Pd−Ir experimental bulk critical temperature. This entropic effect, together with SRO, leads to significant destabilization of low-T Quasi-Janus (QJ) asymmetric configurations of the NP core, which transform to symmetric partially mixed nanophases. First-order and second-order intracore transitions are predicted for dilute and intermediate-range compositions, respectively. Caloric curves computed for the former case yield the NP-size dependent transition latent heat, and in the latter case critical temperatures exhibit a specific scaling behavior. The computed separation diagrams and intracore solubility diagrams reflect enhanced elemental mixing in smaller QJ nanophases. In addition to these diagrams, the revealed near-surface compositional variations are likely to be pertinent to the utilization of Pd−Ir NPs, e.g., in catalysis.

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On the size- and shape-dependence of integral and partial molar Gibbs energies, entropies, enthalpies and inner energies of solid and liquid nano-particles

Kaptay

2024

J Mater Sci

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In this paper the size- and shape dependences of 8 different integral and partial molar thermodynamic quantities are derived for solid and liquid nano-phases, starting from the fundamental equation of Gibbs: i) The integral molar Gibbs energies of nano-phases and the partial molar Gibbs energies of components in those nano-phases, ii) The integral molar enthalpies of nano-phases and the partial molar enthalpies of components in those nano-phases, iii) The integral molar entropies of nano-phases and the partial molar entropies of components in those nano-phases, and iv). The integral molar inner energies of nano-phases and the partial molar inner energies of components in those nano-phases. All these 8 functions are found proportional to the specific surface area of the phase, defined as the ratio of its surface area to its volume. The equations for specific surface areas of phases of different shapes are different, but all of them are inversely proportional to the characteristic size of the phase, such as the diameter of a nano-sphere, the side-length of a nano-cube or the thickness of a thin film. Therefore, the deviations of all properties discussed here from their macroscopic values are inversely proportional to their characteristic sizes. The 8 equations derived in this paper follow strict derivations from the fundamental equation of Gibbs. Only the temperature dependent surface energy of solids and surface tension of liquids will be considered as model equations to simplify the final resulting equations. The theoretical equations are validated for the molar Gibbs energy against the experimental values of liquidus temperatures of pure lead. The theoretical equations for the molar enthalpy are validated i). Against the experimental values of dissolution enthalpy differences between nano- and macro cobalt particles in the same liquid alloy and ii). Against the size dependent melting enthalpy of nano-indium particles. In this way, also the theoretical equations for the molar entropy and molar inner energy are validated as they are closely related to the validated equations for the molar Gibbs energy and molar enthalpy.

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3D phase diagrams and the thermal stability of two-component Janus nanoparticles: effects of size, average composition and temperature

Abstract: Determining binary phase diagrams for nanoparticles proves to be a very difficult task regardless if it is tried either by computer simulations, theoretical considerations or experiments. In this work, using...

Cited by 6 publications

References 52 publications

Effect of Size on the Formation of Solid Solutions in Ag–Cu Nanoparticles

Effect of Size on the Formation of Solid Solutions in Ag–Cu Nanoparticles

The Thermal Stability of Asymmetric Separated Configurations inside Alloy Nanoparticles: Atomic-Scale Modeling of Pd–Ir Nanophase Diagrams

On the size- and shape-dependence of integral and partial molar Gibbs energies, entropies, enthalpies and inner energies of solid and liquid nano-particles

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