Enhanced Electrical Conductivity and Nonstoichiometry in Nanocrystalline CeO2-x

1995 ◽  
Vol 400 ◽  
Author(s):  
E.B. Lavik ◽  
Y.-M. Chiang ◽  
I. Kosacki ◽  
H.L. Tuller
Keyword(s):  
Electrical Conductivity ◽  
Grain Size ◽  
Oxygen Vacancy ◽  
Electronic Conductivity ◽  
Boundary Resistance ◽  
Low Energy ◽  
Coarse Grained ◽  
Size Dependent ◽  
Nanocrystalline Ceria ◽  
Defect Sites

AbstractDense nanocrystalline CeO2-x. of ∼10 nm grain size exhibits enhanced, PO2-dependent electronic conductivity indicative of intrinsic nonstoichiometric behavior under conditions where coarse-grained counterparts are extrinsic. The enthalpy of reduction is lowered by over 2.4 eV per oxygen vacancy. The nanocrystals also exhibit greatly reduced grain boundary resistance, attributed to grain-size-dependent segregation. We propose that interface doping by selected low energy defect sites dominates the defect and transport properties of nanocrystalline ceria, and possibly other nanocrystalline compounds.

Electrical Conductivity of Pure and Doped Nanocrystalline Cerium Oxide

1996 ◽  
Vol 457 ◽  
Author(s):  
E. B. Lavik ◽  
Y.-M. Chiang
Keyword(s):  
Heat Treatment ◽  
Electrical Conductivity ◽  
Grain Size ◽  
Interfacial Area ◽  
Low Energy ◽  
Direct Proportion ◽  
Treatment Conditions ◽  
Defect Sites ◽  
Interface Reduction ◽  
The Relationship

ABSTRACTWe have previously shown that dense nanocrystalline CeO2−x of approximately 10 nm grain size exhibits enhanced electrical conductivity and an enthalpy of reduction that is more than 2.4 eV lower than that for conventional ceria [1, 2]. These effects were attributed to preferential interface reduction. In this work, we investigated the relationship between interfacial area, heat treatment conditions, and conductivity by varying the grain size of dense samples through annealing at various temperatures. It is shown that the conductivity does not scale in direct proportion to interfacial area. Moderate temperature (700 °C) anneals which change the grain size by only a few nanometers reduce the conductivity by three orders of magnitude. It is suggested that atomistic relaxation occurs at the interfaces, and eliminates many low energy defect sites.

Grain Size and Chemical Composition Effects on the Grain Boundary Resistance of Ceria

2002 ◽  
Vol 730 ◽  
Author(s):  
Xiao-Dong Zhou ◽  
Harlan U. Anderson ◽  
Wayne Huebner
Keyword(s):  
Electrical Conductivity ◽  
Grain Size ◽  
Grain Boundary ◽  
Boundary Resistance ◽  
Impedance Spectra ◽  
Total Resistance ◽  
Boundary Area ◽  
Oxygen Ions ◽  
Composition Effects ◽  
Increasing Temperature

AbstractStudies related to the effects of grain size (30nm – 5.0μm) on the electrical conductivity of undoped CeO2 and Ce0.90Gd0.10O1.95 were performed. A series of impedance spectra as a function of temperature and grain size were analyzed. It was found that the ratio of the grain boundary resistance to the total resistance became lower with decreasing grain size, increasing temperature or increasing Gd content. For the case of Gd doped CeO2, the source of the grain boundary resistance may be due to the trapping of oxygen ions in the grain boundary area.

scholarly journals Development of Cube Texture in Coarse Grained Copper

1990 ◽  
Vol 12 (1-3) ◽  
pp. 37-46 ◽  
Author(s):  
M. Sindel ◽  
G. D. Köhlhoff ◽  
K. Lücke ◽  
B. J. Duggan
Keyword(s):  
Grain Size ◽  
Size Effects ◽  
Cube Texture ◽  
Rolling Texture ◽  
Rolling Reduction ◽  
Coarse Grained ◽  
Oriented Growth ◽  
Size Dependent ◽  
Deformation Textures ◽  
Oriented Material

Cube oriented deformed material has been detected in the rolling texture measured on edge sections of heavily rolled coarse grained copper. The level of intensity is low, and seems to be independent of rolling reduction over the range 93–98%. Recrystallization textures show an increasing strength of Cube with rolling reduction. The evidence is consistent with the idea that Cube nuclei are created by a mechanism similar to that proposed by Dillamore and Katoh, and the strength of the recrystallized Cube texture depends on oriented growth. Prior grain size effects are briefly examined and it is shown that deformation textures are less sharp in large grain size compared with small grain sized copper at similar strains. It is likely that the effect of grain size on cube texture formation arises from grain size dependent texture changes in the vicinity of the deformed Cube oriented material.

scholarly journals Comparison of the electrical conductivity of bulk and film Ce1–xZrxO2–δ in oxygen-depleted atmospheres at high temperatures

2021 ◽  
Author(s):  
Iurii Kogut ◽  
Carsten Steiner ◽  
Hendrik Wulfmeier ◽  
Alexander Wollbrink ◽  
Gunter Hagen ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
High Temperatures ◽  
Ionic Conduction ◽  
Electronic Conductivity ◽  
Oxygen Storage ◽  
Coarse Grained ◽  
Reducing Conditions ◽  
Partial Pressures ◽  
Microstructural Effects ◽  
Defect Interactions

AbstractFeaturing high levels of achievable oxygen non-stoichiometry δ, Ce1−xZrxO2−δ solid solutions (CZO) are crucial for application as oxygen storage materials in, for example, automotive three-way catalytic converters (TWC). The use of CZO in form of films combined with simple manufacturing methods is beneficial in view of device miniaturization and reducing of TWC manufacturing costs. In this study, a comparative microstructural and electrochemical characterization of film and conventional bulk CZO is performed using X-ray diffractometry, scanning electron microscopy, and impedance spectroscopy. The films were composed of grains with dimensions of 100 nm or less, and the bulk samples had about 1 µm large grains. The electrical behavior of nanostructured films and coarse-grained bulk CZO (x > 0) was qualitatively similar at high temperatures and under reducing atmospheres. This is explained by dominating effect of Zr addition, which masks microstructural effects on electrical conductivity, enhances the reducibility, and favors strongly electronic conductivity of CZO at temperatures even 200 K lower than those for pure ceria. The nanostructured CeO2 films had much higher electrical conductivity with different trends in dependence on temperature and reducing atmospheres than their bulk counterparts. For the latter, the conductivity was dominantly electronic, and microstructural effects were significant at T < 700 °C. Nanostructural peculiarities of CeO2 films are assumed to induce their more pronounced ionic conduction at medium oxygen partial pressures and relatively low temperatures. The defect interactions in bulk and film CZO under reducing conditions are discussed in the framework of conventional defect models for ceria.

scholarly journals Фазовый состав, микроструктура и электропроводность твердых электролитов HfO_2-R-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- (R=Sc, Y, Ho, Er, Tm, Yb, Lu)

2020 ◽  
Vol 62 (1) ◽  
pp. 145
Author(s):  
А.Н. Мещерских ◽  
А.А. Кольчугин ◽  
Б.Д. Антонов ◽  
Л.А. Дунюшкина
Keyword(s):  
Electrical Conductivity ◽  
Grain Size ◽  
Hafnium Oxide ◽  
Solid Oxide ◽  
Coarse Grained ◽  
Solid Oxide Electrolyte ◽  
Fluorite Type ◽  
Cubic Structure ◽  
Type Lattice ◽  
Oxide Electrolyte

The effect of the addition of 11 mol % R2O3 (R = Sc, Y, Ho, Er, Tm, Yb, Lu) on the phase and elemental composition, microstructure, and electrical conductivity of hafnium oxide was studied. When all additives, with the exception of scandium, are introduced into HfO2, solid solutions with a cubic structure such as fluorite are formed. The HfO2-Sc2O3 sample is an Hf7Sc2O17 phase having a fluorite-type lattice with rhombohedral distortions that undergoes reversible changes in the cubic structure at a temperature of ~ 760 ° C. It has been established that the nature of the dopant practically does not affect the microstructure of the HfO2-R2O3 ceramics; all samples are coarse-grained with a grain size of up to 10 μm. It was shown that the conductivity of HfO2-R2O3 samples is determined by the volume of grains. The most promising materials for use as a solid oxide electrolyte are HfO2-Tm2O3 and HfO2-Yb2O3, in which high conductivity is combined with structural stability.

Revisiting the passivation of stainless steels and other passive CRAs

2018 ◽  
Vol 106 (1) ◽  
pp. 107 ◽  
Author(s):  
Jean- Louis Crolet
Keyword(s):  
Electrical Conductivity ◽  
Metal Ions ◽  
Base Metal ◽  
Stainless Steels ◽  
Electronic Conductivity ◽  
Transport Processes ◽  
General Knowledge ◽  
Inorganic Polymers ◽  
Faraday Cage

All that was said so far about passivity and passivation was indeed based on electrochemical prejudgments, and all based on unverified postulates. However, due the authors’ fame and for lack of anything better, the great many contradictions were carefully ignored. However, when resuming from raw experimental facts and the present general knowledge, it now appears that passivation always begins by the precipitation of a metallic hydroxide gel. Therefore, all the protectiveness mechanisms already known for porous corrosion layers apply, so that this outstanding protectiveness is indeed governed by the chemistry of transport processes throughout the entrapped water. For Al type passivation, the base metal ions only have deep and complete electronic shells, which precludes any electronic conductivity. Then protectiveness can only arise from gel thickening and densification. For Fe type passivation, an incomplete shell of superficial 3d electrons allows an early metallic or semimetallic conductivity in the gel skeleton, at the onset of the very first perfectly ordered inorganic polymers (- MII-O-MIII-O-)n. Then all depends on the acquisition, maintenance or loss of a sufficient electrical conductivity in this Faraday cage. But for both types of passive layers, all the known features can be explained by the chemistry of transport processes, with neither exception nor contradiction.

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