Surface Segregation on Manganese Doped Ceria Nanoparticles and Relationship with Nanostability

Wu, Longjia; Dey, Sanchita; Gong, Mingming; Liu, Feng; Castro, Ricardo H. R.

doi:10.1021/jp508663p

Cited by 67 publications

(81 citation statements)

References 46 publications

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“…The smaller grain size for the lanthanum doped sample already suggests a thermodynamic effect of the dopant on the surface energy of the nanoparticles, as recently proposed. 41 The nanoparticles were subjected to SPS for densification and high densities were achieved (;95% of theoretical value). XRD patterns after densification are also presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

et al. 2015

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Nanocrystalline ceramics offer interesting and useful physical properties attributed to their inherent large volume fraction of grain boundaries. At the same time, these materials are highly unstable, being subjected to severe coarsening when exposed at moderate to high temperatures, limiting operating temperatures and disabling processing conditions. In this work, we designed highly stable nanocrystalline yttria stabilized zirconia (YSZ) by targeting a decrease of average grain boundary (GB) energy, affecting both driving force for growth and mobility of the boundaries. The design was based on fundamental equations governing thermodynamics of nanocrystals, and enabled the selection of lanthanum as an effective dopant which segregates to grain boundaries and lowers the average energy of YSZ boundaries to half. While this would be already responsible for significant coarsening reduction, we further experimentally demonstrate that the GB energy decreases continuously during grain growth caused by the enrichment of boundaries with dopant, enhancing further the stability of the boundaries. The designed composition showed impressive resistance to grain growth at 1100°C as compared to the undoped YSZ and opens the perspective for similar design in other ceramics.

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Section: Resultsmentioning

confidence: 99%

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

et al. 2015

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“…14,22,24 Because no phase separation occurred, or parallel reactions, the released heat was attributed to the change in GB area during the characteristic exothermic peak. GB areas (GBA) were calculated using a tetrakaidecahedral grain shape and a grain size distribution determined by SEM 22,25,26 using the equation…”

Section: Calorimetric Measurement and Grain Growth Studymentioning

confidence: 99%

Direct measurements ofquasi-zero grain boundary energies in ceramics

Nafsin

Castro

2016

J. Mater. Res.

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Nanocrystalline bulk materials (also called nanograined materials) are intrinsically unstable due to the excess grain boundary (GB) free energies. Dopants designed to segregate to boundaries have been proposed to lower excess GB energies, increasing stability against coarsening and enabling nanostructure features to survive high temperature processing and operational environments. It has been theoretically proposed that the GB energy of a material can eventually become zero as a function of dopant concentration, signifying negligible driving force for growth-an infinitely stable nanomaterial. In this work we use ultrasensitive microcalorimetry to experimentally measure the absolute GB energy of gadolinium-doped nanocrystalline zirconia as a function of grain size and show that the energy can indeed reach a quasi-zero energy state (;0.05 J/m 2 ) when a critical GB dopant enrichment is achieved. This thermodynamic condition leads to unprecedented coarsening resistance, but is a temperature dependent function; since increasing temperatures deplete the GB as the dopant dissolves back in the crystalline bulk.

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“…Nanoceramics can only be manufactured when the precursor powders are nanosized and smaller than the desired final size for the nanoceramic. One strategy that has been successfully used to obtain ceramic nanopowders is the use of additives that are segregated at the interfaces (GBs and surfaces) and reduce the interfaces energy, reducing the driving force for particle growth . If additive segregation at the interfaces occurs in nanoscale crystalline domains, the thermodynamic effects of segregation are more evident than those in coarser materials owing to the higher interface density …”

Section: Introductionmentioning

confidence: 99%

“…However, the separation of the kinetic and thermodynamic contributions is difficult with the addition of additives to the material, which are usually seen as physical barriers reducing the GB mobility and are mostly studied as kinetic phenomena. With the advancements of calorimetric techniques for the measurement of the interface energy of nanoparticles, it is possible to show that the surface energy does not remain constant with an increase in the doping content; thus, the nanostability is partially attributed to thermodynamic effects …”

Section: Introductionmentioning

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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Surface Segregation on Manganese Doped Ceria Nanoparticles and Relationship with Nanostability

Cited by 67 publications

References 46 publications

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

Direct measurements ofquasi-zero grain boundary energies in ceramics

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

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Surface Segregation on Manganese Doped Ceria Nanoparticles and Relationship with Nanostability

Cited by 67 publications

References 46 publications

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

Direct measurements ofquasi-zero grain boundary energies in ceramics

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

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Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation