Nanoscale Effects on the Ionic Conductivity of Highly Doped Bulk Nanometric Cerium Oxide

Anselmi‐Tamburini, Umberto; Maglia, Filippo; Chiodelli, Guetano; Tacca, Alessandra; Spinolo, G.; Riello, Pietro; Bucella, Stefania; Munir, Zuhair A.

doi:10.1002/adfm.200500415

Cited by 77 publications

(65 citation statements)

References 45 publications

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“…2 The ability to prepare dense materials and maintain the nanostructure has provided the opportunity to determine heretofore unrecognized nanoscale effects in materials. 3,4 Of the more than 1000 papers on sintering by PECS published in the last decade, few have attempted to provide fundamental understanding of the process 5 and thus the reasons for its superiority over conventional means remain largely not well understood. A common explanation provided in many publications is the role of plasma, proposed to exist between powder particles during sintering.…”

Section: Introductionmentioning

confidence: 99%

Current effects on neck growth in the sintering of copper spheres to copper plates by the pulsed electric current method

Frei

Anselmi‐Tamburini

Munir

2007

Journal of Applied Physics

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The effect of a pulsed dc on the sintering of copper spheres to copper plates was investigated. It was shown that the current had a marked effect on neck growth between the spheres and the plates. The enhancement of sintering under the effect of the current was attributed to electromigration. Microstructural observations on fracture surfaces of necks formed under high currents showed considerable void formation. It was also observed that the current resulted in increased evaporation and the formation of bunched evaporation steps. Formation of these steps and their location relative to the neck were consistent with current density distributions. The results of this investigation provide direct evidence for the role of the current in the sintering in the pulse electric current sintering method.

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Section: Introductionmentioning

confidence: 99%

Current effects on neck growth in the sintering of copper spheres to copper plates by the pulsed electric current method

Frei

Anselmi‐Tamburini

Munir

2007

Journal of Applied Physics

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“…Furthermore, in contrast to spark plasma or hot isostatic pressure sintering, conventional sintering does not reduce the material and hence does not require an additional anneal in oxygen or air prior to electrical characterization. 18 For the measurement of electrical transport properties, metallic electrodes were applied to the opposing sides of the compact disk samples. For the 73 nm and 61 nm grain-sized samples sintered at 1000 and 950…”

mentioning

confidence: 99%

Ionic and Electronic Conductivity of Nanostructured, Samaria-Doped Ceria

Souza¹,

Chueh

Jung

et al. 2012

J. Electrochem. Soc.

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The ionic and electronic conductivities of samaria doped ceria electrolytes, Ce 0.85 Sm 0.15 O 1.925−δ , with nanometric grain size have been evaluated. Nanostructured bulk specimens were obtained using a combination of high specific-surface-area starting materials and suitable sintering profiles under conventional, pressureless conditions. Bulk specimens with relatively high density (≥92% of theoretical density) and low medium grain size (as small as 33 nm) were achieved. Electrical A.C. impedance spectra were recorded over wide temperature (150 to 650 • C) and oxygen partial pressure ranges (0.21 to 10 −31 atm). Under all measurement conditions the total conductivity decreased monotonically with decreasing grain size. In both the electrolytic and mixed conducting regimes this behavior is attributed to the high number density of high resistance grain boundaries. The results suggest a possible variation in effective grain boundary width with grain size, as well as a possible variation in specific grain boundary resistance with decreasing oxygen partial pressure. No evidence appears for either enhanced reducibility or enhanced electronic conductivity upon nanostructuring. The transport and redox properties of ceria have been studied extensively due to the suitability of this material to a wide range of applications including fuel cells (as both electrolyte 1, 2 and anode component [2][3][4][5] ) and catalytic convertors. 6 In recent years there have been observations of 'non-trivial' size effects in ceria in which nanostructuring results in dramatically enhanced conductivity, particularly for grain sizes of <30 nm.7 Concomitant with this change in transport properties is a dramatic increase in reducibility, manifest as a decrease in the standard enthalpy of the reduction reaction. 8 Although the details of the observations differ between authors, the grain boundary behavior of undoped ceria free of intergranular impurity phases is relatively well-explained in terms of a space-charge model. 7,9 In brief, due to inherent differences in the chemical bonding environment at grain boundaries and in the bulk, the grain boundary interface or core displays a charge imbalance between anionic and cationic species leading to an interfacial space-charge potential, φ 0 . This potential, in turn, causes a redistribution of mobile species in the near vicinity of the core, i.e., the space charge region. Inferred values of φ 0 in ceria are ∼0.3 to 0.7 V, and, being positive in sign, imply that vacancies are depleted, whereas electron concentrations, resulting from the Ce 4+ /Ce 3+ equilibrium, are enhanced in the space charge region. The width of the space-charge zone (the effective grain boundary thickness) typically falls between 1.2 and 6 nm. For microcrystalline materials, the consequence is that the grain boundaries serve to block the motion of the predominately mobile oxygen vacancies as they traverse the depletion region and migrate from one grain to the next. For nanocrystalline materials, because the volume fraction of gr...

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“…In several examples, the ionic conductivity increases for nanostructured materials such as CaF2-BaF2 fluoride ion conductors [14], CeO2 oxide ion conducting nanoceramics [15,16], and nanocrystalline LiNbO3 and LiTaO3 lithium ion conductors [17,18]. However, this is not straightforward since the ionic conductivity was found to decrease in other materials when the grain size is reduced [19].…”

Section: Introductionmentioning

confidence: 99%

“…The grain growth of the nanopowder is due to the conventional sintering which includes heating at high temperatures for long durations. Therefore, other innovative sintering techniques such as spark plasma sintering (SPS) could overcome these drawbacks and yield nanoceramic materials [15,16,[20][21][22][23]. SPS experiments, which are performed at a lower temperature and for short time duration (within few minutes) compared to conventional sintering, can successfully minimize grain coarsening during the sintering process that leads to successful fabrication of dense nanomaterials.…”

Section: Introductionmentioning

confidence: 99%

Lithium ionic conduction and relaxation dynamics of spark plasma sintered Li5La3Ta2O12 garnet nanoceramics

Ahmad¹

2016

Nano Online

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which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.In the present work, nanoceramics of Li5La3Ta2O12 (LLT) lithium ion conductors with the garnet-like structure are fabricated by spark plasma sintering (SPS) technique at different temperatures of 850°C, 875°C, and 900°C (SPS-850, SPS-875, and SPS-900). The grain size of the SPS nanoceramics is in the 50 to 100 nm range, indicating minimal grain growth during the SPS experiments. The ionic conduction and relaxation properties of the current garnets are studied by impedance spectroscopy (IS) measurements. The SPS-875 garnets exhibit the highest total Li ionic conductivity of 1.25 × 10−6 S/cm at RT, which is in the same range as the LLT garnets prepared by conventional sintering technique. The high conductivity of SPS-875 sample is due to the enhanced mobility of Li ions by one order of magnitude compared to SPS-850 and SPS-900 ceramics. The concentration of mobile Li+ ions, n c, and their mobility are estimated from the analysis of the conductivity spectra at different temperatures. n c is found to be independent of temperature for the SPS nanoceramics, which implies that the conduction process is controlled by the Li+ mobility. Interestingly, we found that only a small fraction of lithium ions of 3.9% out of the total lithium content are mobile and contribute to the conduction process. Moreover, the relaxation dynamics in the investigated materials have been studied through the electric modulus formalism.

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Nanoscale Effects on the Ionic Conductivity of Highly Doped Bulk Nanometric Cerium Oxide

Cited by 77 publications

References 45 publications

Current effects on neck growth in the sintering of copper spheres to copper plates by the pulsed electric current method

Current effects on neck growth in the sintering of copper spheres to copper plates by the pulsed electric current method

Ionic and Electronic Conductivity of Nanostructured, Samaria-Doped Ceria

Lithium ionic conduction and relaxation dynamics of spark plasma sintered Li5La3Ta2O12 garnet nanoceramics

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