Oxygen potential and defect structure of oxygen-excess pyrochlore Ce2Zr2O7+x

Otobe, Haruyoshi; Nakamura, Akio; Yamashita, Toshiyuki; Minato, Kazuo

doi:10.1016/j.jpcs.2004.07.015

Cited by 26 publications

(23 citation statements)

References 12 publications

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“…Moreover, the X-ray diffraction peaks are narrow, and no other peaks are detected. The Rietveld analysis, Figure 3, shows that this phase is a cerium zirconate tetragonal phase, and are in agreement with the reports on oxidized pyrochlore equimolar cerium zirconate [32,33]. The identification of the four first peaks, from the left, with Miller indices was performed…”

Section: X-ray Diffraction Analysissupporting

confidence: 87%

Equimolar Yttria-Stabilized Zirconia and Samaria-Doped Ceria Solid Solutions

2018

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Compositions of (ZrO 2 ) 0.92 (Y 2 O 3 ) 0.08 (zirconia: 8 mol % yttria-8YSZ) and (CeO 2 ) 0.8 (Sm 2 O 3 ) 0.2 (ceria: 20 mol % samaria-SDC20) ceramic powders were prepared by attrition milling to form an equimolar powder mixture, followed by uniaxial and isostatic pressing. The pellets were quenched to room temperature from 1200 • C, 1300 • C, 1400 • C and 1500 • C to freeze the defects configuration attained at those temperatures. X-ray diffraction analyses, performed in all quenched pellets, show the evolution of the two (8YSZ and SDC20) cubic fluorite structural phases to a single phase at 1500 • C, identified by Rietveld analysis as a tetragonal phase. Impedance spectroscopy analyses were carried out in pellets either quenched or slowly cooled from 1500 • C. Heating the quenched pellets to 1000 • C decreases the electrical resistivity while it increases in the slowly cooled pellets; the decrease is ascribed to annealing of defects created by lattice micro-tensions during quenching while the increase to partial destabilization of the tetragonal phase. Ceramics 2018, 1 344 additions of Y, Yb, Ca, Ti, La, Mg, and Gd oxides as fluorite phase stabilisers [8]; multicomponent rare earth oxides [9]; high entropy single-phase oxide with even 10 components (Gd, La, Nd, Sm, Y, Co, Cr, Fe, Mn and Ni), with a multiphase-single phase reversibility under heating [10]; (Co,Cr,Fe,Mn,Ni) 3 O 4 high entropy oxide with spinel structure [11], high-entropy multicomponent perovskite solid solutions Sr 1−x Ba x (Zr 0.2 Sn 0.2 Ti 0.2 Hf 0.2 A 0.2 )O 3 (x = 0.5, A = Mn, Nb, Ce, Y) [12].It has been suggested that entropy-stabilisation is a "particularly effective compound with ionic character", we investigated this suggestion using equimolar combinations of paradigmatic ionic conductors ZrO 2 : 8 mol % Y 2 O 3 (8YSZ) and CeO 2 : 20 mol % Sm 2 O 3 (SDC20). 8YSZ is already commercially available, as a component of electrochemical devices allowing for the environmentally compatible production of electrical energy, heat, and high-temperature solid oxide fuel cells (800-1000 • C HT-SOFCs) [13][14][15][16][17]. SDC20 was proposed as a candidate to substitute 8YSZ in these devices to enable a decrease in operating temperature to intermediate temperatures (600-800 • C IT-SOFCs) [18][19][20][21].Chemical species are known to be accumulated or depleted at the interfaces of ceramic ionic conductors, creating a space charge region, which is considered to be responsible for the blocking of oxide ions, inhibiting their transport across the grain boundaries. This leads to the grain boundary resistivity detected as a low-frequency semicircle in the impedance diagrams in oxides conventionally sintered [22][23][24][25][26][27][28][29].The purpose of this paper was to look at the distribution of charged species at the interface of solid solutions of equimolar ZrO 2 : 8 mol % Y 2 O 3 and CeO 2 : 20 mol % Sm 2 O 3 , either quenched or slowly cooled from high temperatures, by collecting impedance spectroscopy data.

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Section: X-ray Diffraction Analysissupporting

confidence: 87%

Equimolar Yttria-Stabilized Zirconia and Samaria-Doped Ceria Solid Solutions

2018

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“…With Ce 0.81 Zr 0.19 O 2 , the oxidation enthalpies are much lower in magnitude, -520 kJ/mol O 2 , and are again independent of oxygen stoichiometry so long as the oxygen vacancy concentration is less than the Zr +4 concentration [22]. Based on the observation of steps in the oxygen isotherms at specific stoichiometries [22,23] and the fact that the oxidation enthalpies for ceria-zirconia samples having a wide range of Zr contents are all similar to the heat of oxidation reported for the pyrochlore structure, Ce 2 Zr 2 O 7 [23,38], it has been argued that the redox properties of ceriazirconia solid solutions result from formation of pyrochlore clusters in the bulk structure, with pairs of Zr +4 contributing to two clusters [22,23].…”

Section: Redox Stability Of Ceria-titania Solutions At 973 Kmentioning

confidence: 53%

A thermodynamic investigation of the redox properties of ceria–titania mixed oxides

Gong

Hanson

Gorte

2008

Applied Catalysis A: General

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Ceria-titania solutions with compositions of Ce 0.9 Ti 0.1 O 2 and Ce 0.8 Ti 0.2 O 2 were prepared by the citric-acid (Pechini) method and characterized using x-ray diffraction (XRD) for structure, coulometric titration for redox thermodynamics, and water-gas-shift (WGS) reaction rates. Following calcination at 973 K, XRD suggests that the mixed oxides exist as single-phase, fluorite structures, although there was no significant change in the lattice parameter compared to pure ceria. The mixed oxides are shown to be significantly more reducible than bulk ceria, with enthalpies for reoxidation being approximately-500 kJ/mol O2, compared to-760 kJ/mol O 2 for bulk ceria. However, WGS rates over 1-wt% Pd supported on ceria, Ce 0.8 Ti 0.2 O 2 , and Ce 0.8 Zr 0.2 O 2 were nearly the same. For calcination at 1323 K, the mixed oxides separated into ceria and titania phases, as indicated by both the XRD and thermodynamic results.

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“…This system is much the same as the oxygen potential measurement systems for Pu and Ce oxides used in our previous studies. 7,8 The galvanic cell type in this study is expressed by…”

Section: Methodsmentioning

confidence: 99%

Oxygen Potential Measurement of Americium Oxide by Electromotive Force Method

Otobe

Akabori

Minato

2008

Journal of the American Ceramic Society

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The oxygen potentials of AmO2−x were measured in the x range of 0.01–0.5 and the temperature range of 1000–1333 K by the electromotive force method. The oxygen potentials at 1333 K were −19.83 kJ/mol for x=0.019 and −319.1 kJ/mol for x=0.485, which were higher than those of CeO2−x by approximately 200 kJ/mol for the corresponding x values. From the dependence of the oxygen potentials on x and temperature, a tentative phase diagram of Am–O system was proposed, which suggested the presence of the intermediate phases of Am7O12 and Am9O16 in the Am–O system.

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Oxygen potential and defect structure of oxygen-excess pyrochlore Ce2Zr2O7+x

Cited by 26 publications

References 12 publications

Equimolar Yttria-Stabilized Zirconia and Samaria-Doped Ceria Solid Solutions

Equimolar Yttria-Stabilized Zirconia and Samaria-Doped Ceria Solid Solutions

A thermodynamic investigation of the redox properties of ceria–titania mixed oxides

Oxygen Potential Measurement of Americium Oxide by Electromotive Force Method

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