The grain boundary effect in heavily doped cerium oxide

Tschöpe, Andreas; Kilassonia, S.; Birringer, R.

doi:10.1016/j.ssi.2004.07.052

Cited by 141 publications

(182 citation statements)

References 20 publications

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“…71 This makes comparison of absolute values to other samples difficult, even if they have the same composition. Trends for the different materials should nevertheless be the same, therefore it can be used as a sensitive indicator for changes of the defect chemistry at the grain boundaries.…”

Section: Resultsmentioning

confidence: 99%

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

Neuhaus¹,

Dolle²,

Wiemhöfer³

2018

J. Electrochem. Soc.

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The effect of addition of transition metal oxides on the charge transport of commercially available Gd-doped ceria (Ce 0.9 Gd 0.1 O 2-δ ) was assessed with special emphasis on the electronic partial conductivity. The samples were doped by adding 2, 4 or 6 cat% of CoO 3/4 or FeO 2/3 , or 2 mol% of the transition metal oxides V 2 O 5 , MnO 2 , and CuO, respectively. It was found that even small amounts of transition metal oxides severely change the partial electronic conductivity of ceria while the majority oxygen ion conductivity was only mildly affected: for high oxygen ion conductivity, Fe or Mn oxide addition as well as small amounts of Co oxide are beneficial, as especially the grain boundary conductivity is slightly increased. Addition of V or Cu oxide in contrast increases the minority charge carrier conductivity of electrons and thus enhances the mixed ionic-electronic conductivity. For Co oxide addition, an increasing electronic conductivity with decreasing oxygen partial pressure from 10 −8 to 10 −4 bar at temperatures below 600 • C indicates the changing redox state of Co from divalent at low oxygen partial pressures to trivalent under ambient oxygen partial pressure.

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Section: Resultsmentioning

confidence: 99%

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

Neuhaus¹,

Dolle²,

Wiemhöfer³

2018

J. Electrochem. Soc.

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“…6 This increase in the electronic conductivity was attributed to a decrease in the energy required for the reduction of nanometer size cerium oxide, as compared to coarsened bulk ceramics. These results have been confirmed in numerous reports on ceramics 7 and thin films 8,9 and are now commonly explained in the context of the "space charge model" of grain and grain boundary behavior, as discussed by Tuller,10,11 Tschope et al, 7 and Kim and Maier. 12 The charged defect species which are expected to accumulate at the grain boundary regions to reduce the overall system energy are charge compensated by bulk ionic and electronic defects, leading to a region of space charge which affects the material's transport properties.…”

supporting

confidence: 77%

The Oxygen Permeation Properties of Nanocrystalline CeO[sub 2] Thin Films

Brinkman

Takamura

Tuller

et al. 2010

J. Electrochem. Soc.

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The measurement of oxygen flux across nanocrystalline cerium oxide ͑CeO 2 ͒ thin films at intermediate temperature ͑650-800°C͒ is presented. Porous ceria support substrates were fabricated by sintering with carbon additions. The final dense film was deposited from an optimized sol-gel solution resulting in a mean grain size of 50 nm, which displayed oxygen flux values of up to 0.014 mol/cm 2 s over the oxygen partial pressure range from air to helium gas used in the measurement at 800°C. The oxygen flux characteristics confirm mixed ionic and electronic conductivities in nanocrystalline ceria films and demonstrate the role of size dependent materials properties as a design parameter in functional membranes for oxygen separation.

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“…(c) It is well known that grain boundaries in ceria-based ceramic materials show different defect chemistry as compared to the bulk. [36][37][38] Therefore, it is also an implicit aim of the present study to determine a collection of essential transport properties for single crystals as reference data, in order to judge the role of grain boundaries in studies of polycrystalline material and to get a basic overview of pure bulk properties.…”

Section: +mentioning

confidence: 99%

“…Unfortunately, eqn (37) and none of the interaction models lead to an acceptable fit result. to Ce 3+ at very low pO 2 , which does in no way reproduce the experimental data, which show a ''damping'' of the reduction at low pO 2 .…”

mentioning

confidence: 99%

The model case of an oxygen storage catalyst – non-stoichiometry, point defects and electrical conductivity of single crystalline CeO₂–ZrO₂–Y₂O₃solid solutions

Eufinger

Daniels

Schmale

et al. 2014

Phys. Chem. Chem. Phys.

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The ternary solid solution CeO 2 -ZrO 2 is known for its superior performance as an oxygen storage catalyst in exhaust gas catalysis (e.g. TWC), although the defect chemical background of these outstanding properties is not fully understood quantitatively. Here, a comprehensive experimental study is reported regarding defects and defect-related transport properties of cubic stabilized single crystalline (Ce x Zr 1Àx ) 0.8 Y 0.2 O 1.9Àd (0 r x r 1) solid solutions as a model system for CeO 2 -ZrO 2 . The constant fraction of yttria was chosen in order to fix a defined concentration of oxygen vacancies and to stabilize the cubic fluorite-type lattice for all Ce/Zr ratios. Measurements of the total electrical conductivity, the partial electronic conductivity, the ionic transference number and the non-stoichiometry (oxygen deficiency, oxygen storage capacity) were performed in the oxygen partial pressure range À25 o lg pO 2 /bar o 0 and for temperatures between 500 1C and 750 1C. The total conductivity at low pO 2 is dominated by electronic transport.A strong deviation from the widely accepted ideal solution based point defect model was observed.An extended point defect model was developed using defect activities rather than concentrations in order to describe the point defect reactions in CeO 2 -ZrO 2 -Y 2 O 3 properly. It served to obtain good quantitative agreement with the measured data. By a combination of values for non-stoichiometries and for electronic conductivities, the electron mobility could be calculated as a function of pO 2 , ranging between 10 À2 cm 2 V À1 s À1 and 10 À5 cm 2 V À1 s À1. Finally, the origin of the high oxygen storage capacity and superior catalytic promotion performance at a specific ratio of n(Ce)/n(Zr) E 1 was attributed to two main factors: (1) a strongly enhanced electronic conductivity in the high and medium pO 2 range qualifies the material to be a good mixed conductor, which is essential for a fast oxygen exchange and (2) the equilibrium constant for the reduction exhibits a maximum, which means that the reduction is thermodynamically most favoured just at this composition.

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The grain boundary effect in heavily doped cerium oxide

Cited by 141 publications

References 20 publications

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

The Oxygen Permeation Properties of Nanocrystalline CeO[sub 2] Thin Films

The model case of an oxygen storage catalyst – non-stoichiometry, point defects and electrical conductivity of single crystalline CeO₂–ZrO₂–Y₂O₃solid solutions

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The grain boundary effect in heavily doped cerium oxide

Cited by 141 publications

References 20 publications

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

Assessment of the Effect of Transition Metal Oxide Addition on the Conductivity of Commercial Gd-Doped Ceria

The Oxygen Permeation Properties of Nanocrystalline CeO[sub 2] Thin Films

The model case of an oxygen storage catalyst – non-stoichiometry, point defects and electrical conductivity of single crystalline CeO2–ZrO2–Y2O3solid solutions

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The model case of an oxygen storage catalyst – non-stoichiometry, point defects and electrical conductivity of single crystalline CeO₂–ZrO₂–Y₂O₃solid solutions