Thermodynamic Stability of SnO<sub>2</sub>Nanoparticles: The Role of Interface Energies and Dopants

Chang, Chi-Hsiu; Gong, Mingming; Dey, Sanchita; Liu, Feng; Castro, Ricardo H. R.

doi:10.1021/jp512969k

Cited by 44 publications

(86 citation statements)

References 40 publications

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“…The segregation energetics for nanoxides have been calculated using the Langmuir‐Mclean approach (Equation ) to determine the heat of segregation, as proposed by Chang et al This calculation employs the surface and GB excess obtained via selective lixiviation, as described previously

\frac{x_{j}}{1 - x_{j}} = \frac{x_{b}}{1 - x_{b}} \exp (\frac{normalΔ H_{j}^{seg}}{RT}) with j = S or GB

…”

Section: Resultsmentioning

confidence: 99%

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

et al. 2019

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Manufacturing nanoceramics is challenging owing to the instability of the grain size resulting from the high driving force toward growth associated with the interfaces. Nanometric ceramics of some oxides have exceptional mechanical and optical properties, eg, magnesium aluminate spinel (MgAl 2 O 4 ). The production of these fully conformed ceramics requires a precursor powder, which generally contains sintering-promoting additives. Li salts are typically used as sintering promoters for MgAl 2 O 4 , but the interface stability associated with the segregation of the additive is poorly understood. In this study, MgAl 2 O 4 samples containing 0-2.86 mol% Li ions were synthesized via a simultaneous-precipitation method in an ethylic medium and subsequently calcined at 800°C in air. The nanopowders exhibited only the MgAl 2 O 4 phase, and the crystallite size was determined by the Li 2 O concentration. The crystallite size was changed via the chemical modification of the interfaces by the segregation of Li ions. The solubility in the bulk material was very low at the fabrication temperature, and small amounts of Li ions saturated the bulk material and segregated to the grain boundaries (GBs), significantly stabilizing the grain-grain interface compared with the surface. The resulting powder was then aggregated further owing to the initial stage of sintering. The surface excess obtained via the selective lixiviation method confirmed that the segregation to the GBs was greater than that to the surface. Energetics calculations confirmed these results, indicating a high enthalpy of segregation at the GBs (ΔH segr GB = −52.0 kJ∕mol) compared with that at the surfaces (ΔH segr s = −31.5 kJ/mol). The enthalpy of segregation together with theinterface excess allowed us to estimate the reduction in the interface energy with Li + segregation of 0.8% to the surface and 11.2% to the GBs. The Li + segregation to the surfaces started by Al 3+ substitution, and for powders with ≥1.8 mol% Li ions, Mg +2 was preferentially substituted at the surfaces.

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\frac{x_{j}}{1 - x_{j}} = \frac{x_{b}}{1 - x_{b}} \exp (\frac{normalΔ H_{j}^{seg}}{RT}) with j = S or GB

…”

Section: Resultsmentioning

confidence: 99%

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

et al. 2019

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“…These parameters and corresponding methodologies of measurement have been described in our previous work. 20 3. RESULTS AND DISCUSSION 3.1.…”

Section: Methodsmentioning

confidence: 99%

“…This is consistent with previous simulations 20 and reinforces the fact that particles tend to aggregate by collision, which is in good agreement with many literature reports that mentioned the difficulty of obtaining purely isolated nanoparticles without any organic agent capping. 37,20 The next OA step (ΔH exs ii−iv ) shows roughly 30% of the total energy decrease during OA. This value suggests only moderate driving force for grain reorientation.…”

Section: Methodsmentioning

confidence: 99%

Energetics of Oriented Attachment of Mn-Doped SnO₂ Nanoparticles

2015

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Growth of nanoparticles by oriented attachment (OA) can occur in electrolyte solutions, in vacuum, or even in air. The energy change in this event is determined by the difference between the excess interface energies of the free nanoparticles and the arrangement with attached grains. Therefore, low energy boundaries (highly coherent) are more likely to attach, and after attachment, atomic rearrangement will allow crystals to effectively grow by coalescing two or more grains. However, if the energy of the boundary formed by attachment is low but the activation energy for coalescence is high, it is possible for the system to enter a metastable state that disables nanocrystals' growth (enabling design of growth resistant nanocrystals). In this work, we test this hypothesis in manganese-doped SnO 2 nanoparticles in the absence of organic agents. We observe that manganese dramatically lowers the energies of (noncoherent) grain boundaries of SnO 2 , which enhances nanostability and slows grain growth due to the increased activation energy for OA.

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“…Today, it is well‐known that the interface energy of crystalline solids mainly depends on the structure, crystallographic direction, and surface chemical composition . Considering the chemical composition and type of interfaces, two main extrinsic phenomena are fundamental to the surface energy: gas adsorption for the solid‐gas interface (surface) and segregation of impurities for both solid‐solid interface (grain boundary) and surface …”

Section: Introductionmentioning

confidence: 99%

“…However, the interpretation was only performed for the grain‐boundary segregation in dense materials. Castro et al presented a complete description of manganese ion segregation to the surface and grain boundary of porous SnO 2 nanoparticles and its effect on the interface energies . They measured the surface and grain‐boundary energies using a combination of two methods: water adsorption microcalorimetry and high‐temperature drop solution calorimetry, and they obtained the heat of segregation by estimating the surface excess .…”

Section: Introductionmentioning

confidence: 99%

Surface and grain‐boundary excess of ZnO‐doped SnO₂ nanopowders by the selective lixiviation method

2017

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The primary characteristic of nanopowders is the high surface area and consequently high fraction of atoms on the interfaces, which changes the energy of the system. The additive distribution in the nanopowder interfaces is a fundamental aspect to control the energy, particle size, and final properties of nanopowders. In this work, the surface excess was determined using a selective lixiviation method, where a low‐water‐soluble oxide, SnO2, was used as the matrix, and a high‐water‐soluble oxide, ZnO, was used as the additive. The X‐ray photoelectron spectroscopy (XPS) analysis confirmed that ZnO segregated on SnO2 surfaces. However, after acid lixiviation the same analysis showed an undetectable surface concentration of ZnO. The evaluation of the nanostructure change and surface composition enables us to calculate the heat of segregation for the grain boundary (ΔHsegnormalgb=−47.2kJ·mol−1) and surface (ΔHsegnormals=−36.4kJ·mol−1) and the interface energy reduction because of segregation. At low‐ZnO concentrations, the additive solubilizes in the bulk and promotes particle growth. However, the segregation to the grain boundary and surface determines the relative stability of each interface, which promotes hard agglomeration and particle size stabilization at intermediated ZnO amounts. At high‐ZnO concentrations, the surface segregation stabilizes the solid‐gas interface and decreases the agglomeration and final particle size.

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Thermodynamic Stability of SnO₂Nanoparticles: The Role of Interface Energies and Dopants

Cited by 44 publications

References 40 publications

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Energetics of Oriented Attachment of Mn-Doped SnO₂ Nanoparticles

Surface and grain‐boundary excess of ZnO‐doped SnO₂ nanopowders by the selective lixiviation method

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Thermodynamic Stability of SnO2Nanoparticles: The Role of Interface Energies and Dopants

Cited by 44 publications

References 40 publications

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

Energetics of Oriented Attachment of Mn-Doped SnO2 Nanoparticles

Surface and grain‐boundary excess of ZnO‐doped SnO2 nanopowders by the selective lixiviation method

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Thermodynamic Stability of SnO₂Nanoparticles: The Role of Interface Energies and Dopants

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Energetics of Oriented Attachment of Mn-Doped SnO₂ Nanoparticles

Surface and grain‐boundary excess of ZnO‐doped SnO₂ nanopowders by the selective lixiviation method